reenable recursive resource_mutex

[nobug.git] / README

NoBug
=====
Christian_Thäter,_Benny_Lyons

// doc/overview.txt:1 //
____
Everyone makes mistakes, but with NoBug you won't make them twice!
____

Nobug is a debugging library for instrumenting C and C++ programs
inspired by ideas originating from Design-by-Contract.

Overview
--------

The following features are provided by NoBug:

  * Three different check levels: from detailed to final no-overhead
  * Scope tags: tell whenever a function or loop is considered to be bug free
  * Precondition, Postcondition and Invariant checks and generic assertions
  * Data structures can be dumped
  * Application activities can be logged
  * Runtime customizable logging via an environment variable
  * Different logging targets to stderr, syslog, debugger, ...
  * Annotation of your sourcecode about known bugs, things to do, etc.
  * Tracking resources (files, locks, etc.) used by your program; help in
    detecting misuse
  * Detecting potential deadlocks
  * Simulate errors by injecting faults
  * Additionally, the NoBug project is used to maintain a script and
    some tools to setup testsuites

In contrast to traditional debuggers, NoBug is a non-interactive debugger which
is linked to your application doing hard-coded tests in an efficient,
low-overhead way.

.What NoBug can not do

NoBug is a (macro-)library, it is not a C/C++ language extension. This
means that code must be called at runtime to benefit from the set up
contracts. Whats not tested is likely slipping through the net. Being
part of the program itself it is affected by memory corruption,
certain kinds of misuse may introduce new bugs (test expressions with
side effects for example).

// doc/buildinstall.txt:1 //
Building and Installing
-----------------------

Supported Platforms
~~~~~~~~~~~~~~~~~~~

NoBug has been developed on linux, using gcc. It should be possible to port
it to any other POSIX compliant operating system. Platform/compiler
specific things are kept optional. Currently Linux with a gcc that conforms to
C99 is supported for both 32 and 64 bit architectures.

[grid="all"]
`-------`---------------`---------------`--------------------------------------
CPU     OS              State           Notes
-------------------------------------------------------------------------------
x86_64  Debian          supported       Reference Platform
x86     other Linux     supported       Please report distro specific problems
armel   maemo5          supported       check fails in SDK (emulator bug)
x86*    MacOS X         supported
x86     OpenSolaris     mostly          Builds, but target check fails
        *BSD            planned         Need volunteer for testing
-------------------------------------------------------------------------------

NoBug has no mandatory dependencies on other software and libraries,
some things such as valgrind support are optional and should be automatially
detected during the build, i.e., when ./configure is called.


Release Tarballs
~~~~~~~~~~~~~~~~

Releases are available on:
  http://www.pipapo.org/nobug-releases/

Gpg signed tarballs are being used for distribution. The first step involves
checking the signature:

 $ gpg nobug-VERSION.tar.gz.gpg

This will produce a nobug-VERSION.tar.gz and report if the signature could be
validated.

Since they are built with gnu autotools, the usual build and install procedure
will work:

 $ tar xzvf nobug-VERSION.tar.gz
 $ cd nobug-VERSION
 $ mkdir -p build
 $ cd build
 $ ../configure
 $ make
 $ make check           # optional, run the testsuite
 $ make install         # depending on distribution and setup, do this as root


Development Version via git
~~~~~~~~~~~~~~~~~~~~~~~~~~~
You can obtain a development version by using git.  The git repository can be
cloned via:
`git://git.pipapo.org/nobug` or mirrored at repo.or.cz
`git://repo.or.cz/nobug.git`.

Clone the git repository by:

 $ git clone git://git.pipapo.org/nobug

After cloning the repository, then bootstrap the autotools:

 $ cd nobug
 $ autoreconf -i                # creates the configure file

Then the usual `cd build && ../configure && make && make install` (as above) will work.
Careful users may run `make check` to run a testsuite before installing.


Keeping Git Up To Date
^^^^^^^^^^^^^^^^^^^^^^

To update to any new revision, just enter the nobug dir and

 $ git pull

After that you can build as above (cd build && ../configure && make && make install).
This default pull will update from the 'master' branch which is meant to be an on-going
stable version (latest release + bugfixes).

What Is Installed
~~~~~~~~~~~~~~~~~

Currently, NoBug installs the following:

  * A single nobug.h headerfile. Include this in your code.
  * Static libraries. Statically link these to your application:
    - `libnobug.a` for singlethreaded programs.
    - `libnobugmt.a` for multithreaded programs.
  * Dynamic Libraries. Dynamically link these to your application:
    - `libnobug.so` for singlethreaded programs.
    - `libnobugmt.so` for multithreaded programs.
    - associated libtool descriptors (`libnobug*.la`)
  * Pkgconfig control files:
    - `nobug.pc` for singlethreaded programs.
    - `nobugmt.pc` for multithreaded programs.
  * The `nobug_rbdump` utility to inspect NoBug ringbuffers.


.Generating This Documentation

 $ make nobug_manual.txt
 $ ascidoc -a toc nobug_manual.txt

// doc/using.txt:1 //
Using NoBug
-----------

Your application will have to include the header file 'nobug.h' before NoBug
can be used:

 #include "nobug.h"


Once you've included the NoBug API in your application, you'll then have to select
a 'build-level'.  Build-levels are discussed later, c.f., 
xref:buildlevel[buildlevel].   Build-levels are used to define the amount of
information NoBug provides to you.  Maximum information is generally required while
developing an application and the ALPHA build-level is most apropriate during
this phase; whereas the released phase of an application will usually only require
sparse information, for which the RELEASE build-level has been conceived.

A build-level must always be specified, otherwise the compiler will complain
while attempting to compile your application.  You can specifiy a build level in
one of two ways: use a define statement in one of your modules, or pass the
build-level using the -D flag to your compiler.  Assuming we'd like to select
the ALPHA build-level in your application, then your module would assume the
following form:


 #define EBUG_ALPHA
 #include "nobug.h"



Subsequently you'll have to link the appropriate library to your application.

A number of different libraries are available to link depending on whether you
require to statically or dynamically link, or whether your application is multi
or single threaded.  The link order is important on your link line.  Link the NoBug
library 'after' your application's modules.  Here's how to statically link,
single-threaded applications:

[source,sh]
----------------
gcc -o mybinary $(WHATEVER_FLAGS) mymodule1.o ... mymodulen.o  ..../libs/libnobug.a 
----------------

However, for more flexibility in selecting a build-level, you might wish to
define various targets in your makefile, one for each build-level.  In such
cases, the -D flag in your makefile is most appropriate; so your link line for
an ALPHA build with multi-threaded support would look like the following: 
 
[source,sh]
----------------
gcc -o mybinary -DEBUG_ALPHA $(WHATEVER_FLAGS) mymodule1.o ... mymodulen.o  ..../libs/libnobugmt.a 
----------------

Both libraries must be initialised  before they can be used.  There are a number
of different ways to initialise the NoBug libraries.  One of the easiest ways
to initialise the NoBug libraries is to use the `NOBUG_INIT` macro, which must
be used before any features can be used or any thread is created. This is
discussed in more detail in the xref:multithreading[multithreading] chapter.  

So putting all this together, our application using NoBug might look something
like the following:


[source,sh]
----------------
#include "nobug.h"   /* Include the NoBug API */
#define EBUG_ALPHA   /* If we have not used the -D Flag in our makefile */

int main()
{
        NOBUG_INIT;  /* Initialise NoBug libs */

        ...
}
----------------






Many aspects of NoBug can be configured by overriding macros before 'nobug.h' is
included. 

A project using NoBug can use autoconf to check for execinfo and
valgrind:

 AC_CHECK_HEADER([execinfo.h], AC_DEFINE(HAVE_EXECINFO_H))
 PKG_HAVE_DEFINE_WITH_MODULES(VALGRIND, [valgrind])

For Multithreaded programs, you should also check for the availability of pthreads
and flavour

 ACX_PTHREAD

When the resulting `HAVE_PTHREAD`, `HAVE_EXECINFO_H` and
`HAVE_VALGRIND_H` are defined by the configure script, the
relevant features become available.

NoBug then defines `NOBUG_USE_PTHREAD`, `NOBUG_USE_VALGRIND` and
`NOBUG_USE_EXECINFO` to 1. If you do not want to use any of these features in
NoBug, you can override these macros by setting to 0 before including nobug.h.

If `NVALGRIND` is defined, there will be no support for valgrind.



There are many other macros which can be set and overridden by the user to
control behavior. Your help would be appreciated in expanding this documentation
if you find some features useful; or simply contact any of the authors.



.Using Nobug from a Project using autoconf
[source,sh]
----------------
PKG_CHECK_MODULES(NOBUGMT_LUMIERA, [nobugmt >= 0.3rc1],
                                 AC_DEFINE(HAVE_NOBUGMT_H),
                                 AC_MSG_ERROR([NoBug pkg-config metadata missing])
)
----------------

// doc/additional.txt:1 //
Checking for Additional Tools
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Various peripheral tools can be used by NoBug depending on the requirements
of the application and the detail desired by the user.  Such tools can provide
additional, detailed information on the application and its behaviour.
However, some applications may not require such detail and the associated
overhead in information, and users may decide to omit excess information by
excluding such tools.

At the moment NoBug supports the optional inclusion of gdb, valgrind and support
for multi-threaded applications and the information that can be provided by
these tools.  However, support for other tools may be supplied in the future,
e.g. the dbx debugger on OpenSolaris. 

Such tools can be easily queried on the system and if they are available on a
particular system, they can be used by NoBug to provide even more information on
the application using NoBug.  If such tools are not available or are not
required by the user for one reason or other, then NoBug will happily function
as usual, just without the extra information.

Testing the availability of such tools on a particular system can be achieved
using autoconf, as illustrated in the following:

`*NOBUG_USE_VALGRIND*`::
   `1`:: Use valgrind
   `0`:: Do not use valgrind

`*NOBUG_USE_PTHREAD*`::
   `1`:: Support for multi-thread applications
   `0`:: Single-threaded applications

`*NOBUG_USE_EXECINFO*`::
   `1`:: Backtrace information
   `0`:: No backtrace information

These macros are then automatically defined when the configuration system
provides the associated `HAVE_*` macros, but can then be overridden by the user,
depending on the user's requirements.


// doc/whichlibrary.txt:1 //
Link Appropriate Library
~~~~~~~~~~~~~~~~~~~~~~~~

Finally, the appropriate library (for either single or multi-threaded
applications) is linked to the project.

   *libnobug*:: Link-in this library for single threaded applications.
   *libnobugmt*:: Link with this library for multi-threaded applications.

NoBug installed static and dynamic libraries. When your application
uses multiple dynamic libraries which use NoBug or you build a dynamic
library, then you have to link against the dynamic library.

You can use the `pkg-config` tool to gather information about NoBug in
your build system.

Release builds remove all assertions, but logging is still kept. We
make the assumption that bugs which were not covered in alpha and beta
builds will not easily show up in releases because the assertions
there were not sufficient. Furthermore, end users are not test bunnies
and will not provide good bug reports anyway. If there is a problem in
a release build, try to track down the cause using a beta build from
the same source.

// doc/initialization.txt:1 //
Initialization
--------------

Global init
~~~~~~~~~~~

Before anything from NoBug can be used, NoBug must be initialised.  This is
performed by calling one of the `NOBUG_INIT_` macros.

The simpliest such macro among the initialising set is the following:

  NOBUG_INIT()

`NOBUG_INIT` can be called more than once, subsequent calls will be a no-op,
thus initialising in main and in libraries won't interfere with one another.

In other words, `NOBUG_INIT` is usually the first call to NoBug.

.Destroying NoBug
Since NoBug is intended to be available throughout its whole lifetime,
destroying it is not to be advised. Nevertheless, there is a destroy function
 void nobug_destroy (void)

to shutdown NoBug, and this frees all resources associated with it.
This is mostly used in the NoBug testsuite itself to check for leaks,
and it might be useful for other programs which employ some kind of
leak checker.

Init logging Flags
~~~~~~~~~~~~~~~~~~

If you want to use environment variable controlled debuging, then you have to
initialize each defined flag with

  NOBUG_INIT_FLAG(flagname)

or

  NOBUG_INIT_FLAG_LIMIT(flagname, default)

or one of the C++ compatibility macros.

This is documented later in the xref:logconfig[logging configuration] chapter.

Threads
~~~~~~~

In Multithreaded programs you should assign an identifier to each
thread. A thread identifier is a string which will be automatically
appended with an underscore and a incrementing integer. It is is created with:

  NOBUG_THREAD_ID_SET(name)

Calling `NOBUG_THREAD_ID_SET("worker")` will yield in a thread
identifier 'worker_1' for example.

If you don't set an identifier, then NoBug will assign an automatic one.
This is further documented in the xref:multithreading[multi threading]
section of this manual.

[[initexample]]
.Initialization
[source,c]
-------------------------------------------------------
#include "nobug.h"
NOBUG_DEFINE_FLAG(example);

...

int main()
{
    NOBUG_INIT();
    NOBUG_THREAD_ID_SET("main");
    NOBUG_INIT_FLAG(example);

    ...
}
-------------------------------------------------------

// doc/buildlevels.txt:1 //
[[buildlevel]]
Debugging Information Granuality: The Build Levels
--------------------------------------------------

There are three different levels of debugging information available: alpha, beta
and release.  One of these levels must be specified before compiling, otherwise
an error while compiling will occur.


  *ALPHA*::
        This debugging level is envisaged for the development phase of a project
        where exhaustive testing and logging are required.
  *BETA*::
        This debugging level is more appropriate for projects beyond the
        development phase and ready for trials in the field and users willing to
        test the software.
  *RELEASE*::
        This level is for final, end-users.

.Select a Build Level
A logging level can be selected by either using a define in one of the
applications' modules, or by passing the appropriate level using the -D switch
to the compiler:

    *ALPHA*::   -DEBUG_ALPHA (`#define EBUG_ALPHA`)

    *BETA*::    -DEBUG_BETA (`#define EBUG_BETA`)

    *RELEASE*:: -DNDEBUG (`#define NDEBUG`)

If none of the above switches has been set, NoBug will abort the
compilation with an error.

// doc/logging.txt:1 //
Logging
-------

Nearly all NoBug Macros emit some log message. NoBug gives the user fine
grained control over these log messages to display only interesting information
without loosing details.

Log messages can be routed to various destinations.  The following destintaions
are available: 

  *RINGBUFFER*::
        The underlying storage backend. Messages are appended to the
        end of the buffer, overwriting older messages at the front of
        the buffer. NoBug comes with a highly efficient ringbuffer
        implementation. This ringbuffer is temporary by default but
        can be made persistent on disk which can be inspected with the
        'nobug_rbdump' tool.

  *CONSOLE*::
        This is either just stderr, or, if running under a supported
        debugger, the debuggers facilities to print messages will be used.

  *FILE*::
        The user can open files for log messages.

  *SYSLOG*::
        Messages are sent to the standard system logging daemon.

  *APPLICATION*::
        There are hooks which allow the programmer to catch logmessages and
        display them in an application which are defined by the application.

Each logmessage has a priority describing its severity in the same way as
syslog messages do.

All non-fatal messages are associated with a programmer defined flag describing
the source of the message (subsystem, module, ...).

Putting this all together: A user can define which source/flag will be logged at
what priority level and to which destination. To make this all easier, NoBug
tries to provide reasonable defaults.

// doc/logconfiguration.txt:1 //
[[logconfig]]
Configuration
~~~~~~~~~~~~~

.Log Levels

Each log macro has an explicit or implicit log-level which
correspondends to syslog levels. Logging is only emitted when the
message is more severe or the same as a defined limit.

[[logdefaults]]
.Default levels for logging
[grid="all"]
`````~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
             , ALPHA, BETA   , RELEASE,
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*ringbuffer* , TRACE, INFO   , NOTICE , ringbuffer must always be most verbose
*console*    , INFO , NOTICE , -1     , no log to console in release
*file*       , TRACE, NOTICE , WARNING,
*syslog*     , -1   , NOTICE , WARNING, no syslog for test runs
*application*, INFO , WARNING, ERROR  ,
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Depending on the build level, there is a default logging target and a default
limit which is selected when the user doesn't specify one.

The following default limits are available:

  * In *ALPHA* builds, `NOBUG_LOG_LIMIT_ALPHA` is used which defaults to `LOG_INFO`
  * In *BETA* builds, `NOBUG_LOG_LIMIT_BETA` is used and defaults to `LOG_WARNING`
  * In *RELEASE* builds, `NOBUG_LOG_LIMIT_RELEASE` is used and defaults to `LOG_CRIT`

The default targets are:

  * In *ALPHA* builds, `NOBUG_LOG_TARGET_ALPHA` is used which defaults to
    `NOBUG_TARGET_CONSOLE`
  * In *BETA* builds, `NOBUG_LOG_TARGET_BETA` is used and defaults to
    `NOBUG_TARGET_FILE`
  * In *RELEASE* builds, `NOBUG_LOG_TARGET_RELEASE` is used and defaults to
    `NOBUG_TARGET_SYSLOG`


You can override all these values with your own values. As an alternative,
`NOBUG_LOG_LIMIT` and `NOBUG_LOG_TARGET` can be defined before
including "nobug.h" to override all defaults.

// doc/logflags.txt:1 //
[[logflags]]
Log Flags
~~~~~~~~~

Flags are used to inform NoBug about subsystems/modules or even finer
grained sections of the code. These are referred to as 'channels' in other 
logging libraries.

A flag should be declared in a headerfile using the following mechanism:

[[DECLARE_FLAG]]
 NOBUG_DECLARE_FLAG(flagname)

It is advisable to do so in one of your header files.

Furthermore, the flag must be defined in some implementation file by using one
of the following schemes:

[[DEFINE_FLAG]]
 NOBUG_DEFINE_FLAG(flagname)

or:

[[DEFINE_FLAG_LIMIT]]
 NOBUG_DEFINE_FLAG_LIMIT(flagname, limit)

Moreover, macros are available that accept a 'parent' flag as a parameter, which is then
used to initialize the defaults from another flag:

[[DEFINE_FLAG_PARENT]]
 NOBUG_DEFINE_FLAG_PARENT(flagname, parent)

or

[[DEFINE_FLAG_PARENT_LIMIT]]
 NOBUG_DEFINE_FLAG_PARENT_LIMIT(flagname, parent, limit)

This can be used to create hierachies of flags


[[Cplusplus_logflags]]
.C++ support, C++ logflags

Additional macros are available for applications written in C++:

 NOBUG_CPP_DEFINE_FLAG(name)
 NOBUG_CPP_DEFINE_FLAG_PARENT(name, parent)
 NOBUG_CPP_DEFINE_FLAG_LIMIT(name, default)
 NOBUG_CPP_DEFINE_FLAG_PARENT_LIMIT(name, parent, default)

These macros statically initialize the flags when they are defined, there is no
need to call `NOBUG_INIT_FLAG()` (see below).


.Force declarations only

When the the following preprocessor constant is defined to be `1`:

[[DECLARE_ONLY]]
 NOBUG_DECLARE_ONLY

then *all* definitions here (`NOBUG_DEFINE_*`)
become declarations only.  When this is defined to be `0` (which is the
default) then all definitions behave as described.
This can be used to construct a headerfile which only contains
definitions, but, by default, yield only declarations. This provides one
convenient single point to maintain flag configurations.

.Maintaining flags in a single header 'flags.h'
[source,c]
----
#include <nobug.h>

/*
 if not included from flags.c then declare the flags,
 else define them
 */
#ifndef FLAGS_C
#define NOBUG_DECLARE_ONLY 1
#endif

/* use only DEFINE_FLAG here */
NOBUG_DEFINE_FLAG(example);

/*
 Reset it to 0 to cause no trouble
 */
#ifndef FLAGS_C
#undef NOBUG_DECLARE_ONLY
#define NOBUG_DECLARE_ONLY 0
#endif
----

.flags.c
[source,c]
----
#define FLAGS_C
#include "flags.h"
...
----


.Logging Flag Initialization

Next you should call

 NOBUG_INIT_FLAG(flagname)

or

 NOBUG_INIT_FLAG_LIMIT(flagname, default)

once at the start of your program for each flag.

For flags defined with `NOBUG_DEFINE_FLAG(flagname)` the defaults are initialized
as in the xref:logdefaults[table above], while
`NOBUG_DEFINE_FLAG_LIMIT(flagname, level)` is used to initialize the
default target (depending on build level) to `level`.

// doc/logflagsenv.txt:1 //
[[NOBUG_ENV]]
Control what gets logged
~~~~~~~~~~~~~~~~~~~~~~~~

The `NOBUG_INIT_FLAG...` calls parsing the environment variable
'NOBUG_LOG' to configure what gets logged at runtime. The syntax is as
following:

.Formal Syntax for log control
[source,prolog]
----
 logdecl_list --> logdecl, any( ',' logdecl_list).

 logdecl --> flag, opt(limitdecl, any(targetdecl)).

 flag --> "identifier of a flag".

 limitdecl --> ':', "LIMITNAME".

 targetdecl --> '@', "targetname", opt(targetopts).

 targetopts --> '(', "options for target", ')', opt(targetopts).
----

Roughly speaking, 'NOBUG_LOG' contains a comma separated list of declarations for
flags which are the name of the flag followed by a limit which is written in
all uppercase letters and preceeded by a colon, followed by target declarations
which are names of the targets, introduced by a at sign. Target declarations
can have option, described in the next section. Limit and target
declarations are optional and then choosen from the defaults table above. These
defaults are currently just an guess what should be useable and might be
redefined in future.

.Targets and Options

The Following options are available:

 `@ringbuffer`::
   `(file=_filename_)`:: set filename backing the ringbuffer
   `(size=_nnn_)`::      set size of the ringbuffer
   `(append)`::          don't erase existing ringbuffer
   `(keep)`::            keep file after application end
   `(temp)`::            unlink file instantly at creation

 `@console`::
   `(fd=n)`::            redirect console output to fd n

 `@file`::
   `(name=_filename_)`:: log to filename
   `(append)`::          append to (existing) log

 `@syslog`::
   `(ident=_name_)`::    global prefix for syslog
   `(cons)`::            log to system console if syslog is down
   `(pid)`::             include pid in log
   `(perror)`::          log to stderr as well


.How the NOBUG_LOG is used
[source,sh]
----
# set the limit of the default target a default limit (see table above)
NOBUG_LOG='flag,other'

# set the limit of the default target to DEBUG
NOBUG_LOG='flag:DEBUG'

# set console and syslog limits for flag to DEBUG
NOBUG_LOG='flag:DEBUG@console@syslog'

# trace 'other' to a persistent ringbuffer
NOBUG_LOG='other:TRACE@ringbuffer(file=log.rb)(size=8192)(keep)'
----

.Using log flags (example.c)
[source,c]
----
#include "nobug.h"

NOBUG_DEFINE_FLAG (test);

int main()
{
   /* NOBUG_INIT;  // not needed because of NOBUG_INIT_FLAG */
   NOBUG_INIT_FLAG (test);

   TRACE (test, "Logging enabled");
   TRACE (NOBUG_ON, "Always on");
}
----

.test it:
[source,sh]
----
$ cc -DEBUG_ALPHA -lnobug example.c
$ ./a.out
0000000002: TRACE: example.c:11: main: Always on

$ NOBUG_LOG=test:TRACE ./a.out
0000000001: TRACE: example.c:10: main: Logging enabled
0000000002: TRACE: example.c:11: main: Always on
----

// src/nobug.c:38 //
Predefined Flags
~~~~~~~~~~~~~~~~

There are some debugging flags which are predefined by NoBug.

[[NOBUG_ON]]
.NOBUG_ON

The flag `NOBUG_ON` is always enabled at LOG_DEBUG level. This is
static and can not be changed.

[[NOBUG_ANN]]
.NOBUG_ANN

The flag `NOBUG_ANN` is used for the source annotations. This is
static and can not be changed. It differs from `NOBUG_ON` as in
never logging to syslog and only define a LOG_WARNING limit for the
application callback.

[[nobug_flag]]
.nobug (flag)

Actions on NoBug itself will be logged under the `nobug` flag itself.
When you want to see whats going on (useful to check if you call
`NOBUG_INIT_FLAG()` on all flags) you can enable it with `NOBUG_LOG=nobug:TRACE`.

// doc/macros.txt:1 //
Macros
------

The NoBug interface is almost completely implemented using
preprocessor macros. This is required because NoBug uses the
`+++__FILE__+++`, `+++__LINE__+++` and `+++__func__+++` macros to
log information on the current file, line number and function.
Moreover, all the flat namespace uppercase identifiers make it ease
to recognise the macros in source code.

All macros are available without condition with a `NOBUG_...` prefix.
Many macros (the common cases) are also available without this prefix
as a convenience, however macros without this prefix must not have
been previously defined. When `NOBUG_DISABLE_SHORTNAMES` is defined
before including 'nobug.h', then only the `NOBUG_` prefixed macros
are available and the short forms will never be defined.

A set of macros are provided by NoBug that are postfixed by `..._IF`.
These macros have the following form:

  * `..._IF(when, ...)`

They perform the desired action only if `when` is true. For example:

  * `REQUIRE_IF(foo != NULL, foo->something == constrained)`

The assertion will only be performed if `foo` is non `NULL`.

NoBug also also contains a facility to pass the source context (file,
line, function) around, this can be used to write functions which
handle things where one is more interested in the context of the caller
than the location where the macros appears.

This macros are postfixed with `..._CTX` and take an extra context
parameter (usually at last but before the logging format specifier and
any variable argument list). The context parameter must be of type
`const struct nobug_context`.

When the `_CTX` context form is used together with the conditional `_IF`
form then the suffix of the macros is always `..._IF_CTX`.

The macros which take a context have no short form and must always be
prefixed with `NOBUG_...`.

// doc/parametertable.txt:1 //
Parameters types
~~~~~~~~~~~~~~~~

We use names for parameters which describe their type. These names are
orthogonal through all macro definitions.

[grid="all"]
`---------`------------------------------------------------------------------
`when`    Assertion is only performed if expression `when` is true at runtime
`expr`    Test without side effects
`flag`    Flag to enable custom logging groups
`type`    Data type to be checked as a single identifier name
`pointer` Pointer to type
`lvl`     Log level
`depth`   Depth for invariants and dumps
`context` Source context of type `struct nobug_context`
`...`     printf-like format string followed by its arguments
---------------------------------------------------------------------------

// src/nobug.h:629 //
[[NOBUG_CONTEXT]]
Source Contexts
~~~~~~~~~~~~~~~
 NOBUG_CONTEXT
 NOBUG_CONTEXT_NOFUNC

NoBug passes information about the source location of a given statement in
`const struct nobug_context` structures. These can be generated with
`NOBUG_CONTEXT` or `NOBUG_CONTEXT_NOFUNC`. The later one doesn't define a
function name and must be used when the function context is not available
like in static initialization etc..

// src/nobug.h:104 //
Assertions
----------

[[CHECK]]
.CHECK
 CHECK(expr, ...)
 CHECK_IF(when, expr, ...)

This assertion is never optimized out. Its main purpose is for implementing
testsuites where one want to assert tests independent of the build level

[[REQUIRE]]
.REQUIRE
 REQUIRE(expr, ...)
 REQUIRE_IF(when, expr, ...)
 NOBUG_REQUIRE_CTX(expr, context,...)
 NOBUG_REQUIRE_IF_CTX(when, expr, context, ...)

Precondition (input) check. Use these macros to validate input a
function receives. The checks are enabled in *ALPHA* and *BETA* builds and
optimized out in *RELEASE* builds.

[[ENSURE]]
.ENSURE
 ENSURE(expr, ...)
 ENSURE_IF(when, expr, ...)
 NOBUG_ENSURE_CTX(expr, context, ...)
 NOBUG_ENSURE_IF_CTX(when, expr, context, ...)

Postcondition (progress/output) check. Use these macros to validate the
data a function produces (example: return value). `ENSURE` is enabled
unconditionally in *ALPHA* builds and optimized out in *BETA* builds for
scopes which are tagged as `CHECKED`.

The `ENSURE_IF` variants are enabled in *ALPHA* and *BETA* builds.

In *RELEASE* builds this checks are
always optimized out, scopes tagged as `UNCHECKED` are not permitted.

[[ASSERT]]
.ASSERT
 ASSERT(expr, ...)
 ASSERT_IF(when, expr, ...)
 NOBUG_ASSERT_CTX(expr, context, ...)
 NOBUG_ASSERT_IF_CTX(when, expr, context, ...)

Generic check. Use these macros when you want to validate something
which doesn't fall into one of the above categories. A example is when
a library function can return a unexpected result (scanf with syntax
error in the formatstring, when a constant/literal formatstring is
expected). The checks are enabled in *ALPHA* and *BETA* builds and
optimized out in *RELEASE* builds.

[[assert]]
.assert
 assert(expr)

NoBug overrides the standard `assert` macro, using `NOBUG_ASSERT`.
This is just a compatibility feature, its use is not suggested.

[[INVARIANT]]
.INVARIANT
 INVARIANT(type, pointer, depth)
 INVARIANT_IF(when,type, pointer, depth)
 INVARIANT_ASSERT(expr, ...)

Checking invariants. You can provide more complex checking functions
which test the validity of datastructures. Invariants are only enabled
in *ALPHA* builds for scopes which are not tagged as `CHECKED` and
otherwise optimized out.

 TODO: describe how to create invariant checks

// src/nobug.h:363 //
Logging Macros
--------------

Logging targets a flag (except for `ECHO`) and is done at a log-level relating to syslog levels.

NOTE: there is no logging macro for `LOG_EMERG`, this is only used by the assertions as fatal message

[[ECHO]]
.ECHO
 ECHO(...)

Never optimized out, logs at LOG_NOTICE level. Its main purpose is for implementing
testsuites where one want to print and log messages independent of the build level

[[ALERT]]
.ALERT
 ALERT(flag, ...)
 ALERT_IF(when, flag, ...)
 NOBUG_ALERT_CTX(flag, context, ...)
 NOBUG_ALERT_IF_CTX(when, flag, context, ...)

This is the most critical condition an application might log. This might be used
if an error occurs which can not be handled except a safe shutdown for example.

[[CRITICAL]]
.CRITICAL
 CRITICAL(flag, ...)
 CRITICAL_IF(when, flag, ...)
 NOBUG_CRITICAL_CTX(flag, context, ...)
 NOBUG_CRITICAL_IF_CTX(when, flag, context, ...)

An error which can not be handled occured but the application does not need to be
shutdowen, perhaps waiting for an operator to fix the cause.

[[ERROR]]
.ERROR
 ERROR(flag, ...)
 ERROR_IF(when, flag, ...)
 NOBUG_ERROR_CTX(flag, context, ...)
 NOBUG_ERROR_IF_CTX(when, flag, context, ...)

Application takes a error handling brach

[[WARN]]
.WARN
 WARN(flag, ...)
 WARN_IF(when, flag, ...)
 NOBUG_WARN_CTX(flag, context, ...)
 NOBUG_WARN_IF_CTX(when, flag, context, ...)

Rare, handled but unexpected branch

[[INFO]]
.INFO
 INFO(flag, ...)
 INFO_IF(when, flag, ...)
 NOBUG_INFO_CTX(flag, context, ...)
 NOBUG_INFO_IF_CTX(when, flag, context, ...)

Message about program progress

[[NOTICE]]
.NOTICE
 NOTICE(flag, ...)
 NOTICE_IF(when, flag, ...)
 NOBUG_NOTICE_CTX(flag, context, ...)
 NOBUG_NOTICE_IF_CTX(when, flag, context, ...)

More detailed progress message

[[TRACE]]
.TRACE
 TRACE(flag, ...)
 TRACE_IF(when, flag, ...)
 NOBUG_TRACE_CTX(flag, context, ...)
 NOBUG_TRACE_IF_CTX(when, flag, context, ...)

Very fine grained messages

NOTE: that `TRACE` corresponds to `LOG_DEBUG`, because using `DEBUG` could be ambiguous.

[[LOG]]
.LOG
 NOBUG_LOG_CTX(flag, lvl, context, ...)
 NOBUG_LOG_IF_CTX(when, flag, lvl, context, ...)

Generic logging macro which takes the level explicitly,
avoid this, unless you implement your own logging facilities.

[[LOG_BASELIMIT]]
.LOG_BASELIMIT
 NOBUG_LOG_BASELIMIT_ALPHA
 NOBUG_LOG_BASELIMIT_BETA
 NOBUG_LOG_BASELIMIT_RELEASE
 NOBUG_LOG_BASELIMIT

anything more detailed than this base limits will be optimized out.
This is used to reduce the logging overhead for *RELEASE* builds.
By default the limit is set to `LOG_DEBUG` for *ALPHA* and *BETA*
builds, so all logging is retained and `LOG_NOTICE` in *RELEASE*
builds to log the application progress only coarsely then.

This macros can be defined before including 'nobug.h' to some other
log level (as defined in 'syslog.h').

// doc/dumping.txt:1 //
[[dumping]]
Dumping Datastructures
----------------------

TODO How to write DUMP handlers

One can write functions for dumping complex datastructures using the NoBug
facilities. This is done by writing a custom function for each
datastructure to be dumped which may recursively call other dumping
functions. There are macros for logging within such a dumper function
and for initiating a dump of a given datastructure.

// src/nobug.h:309 //
[[DUMP]]
.DUMP
 DUMP(flag, type, pointer, depth)
 DUMP_IF(when, flag, type, pointer, depth)

This macros call a datastructure dump of the object (`pointer`) in question.
`DUMP` is only available in *ALPHA* and *BETA* builds, `DUMP_IF` is also
enabled for the RELEASE builds.

[[DUMP_LOG]]
.DUMP_LOG
 DUMP_LOG(...)
 DUMP_LOG_IF(when, ...)

Any output from `DUMP` handlers should be done by these macros.

Dumping is by default done on level `LOG_DEBUG`, this can be overridden by
defining `NOBUG_DUMP_LEVEL` to some other level.

// doc/dumpexample.txt:1 //
.How to use the DUMP facilities

[source,c]
-------------------------------------------------------
struct STRUCTNAME
{
  int INTEGER_MEMBER;
  char * STRING_MEMBER;
  struct STRUCTNAME* next;
}
-------------------------------------------------------

then you define a function like:

[source,c]
-------------------------------------------------------
void
nobug_STRUCTNAME_dump (const struct STRUCTNAME* self,
                       const int depth,
                       const char* file,
                       const int line,
                       const char* func)
{
  // check for self != NULL and that the depth
  // limit did not exceed in recursive datastructures
  if (self && depth)
  {
    // use DUMP_LOG not LOG to print the data
    DUMP_LOG("STRUCTNAME %p: int is %d, string is %s", self,
                             self->INTEGER_MEMBER,
                             self->STRING_MEMBER);
    // now recurse with decremented depth
    nobug_STRUCTNAME_dump (self->next, depth-1, file, line, func);
  }
}
-------------------------------------------------------

now you can use the DUMP() macros within the code

[source,c]
-------------------------------------------------------
example()
{
  struct STRUCTNAME foo;
  init(&foo);
  DUMP (my_flag, STRUCTNAME, &foo, 2);
}
-------------------------------------------------------

// src/nobug.h:649 //
Source Annotations
------------------

One can tag features as:

[[DEPRECATED]]
.DEPRECATED
 DEPRECATED(...)

Something which shouldn't be used in future

[[UNIMPLEMENTED]]
.UNIMPLEMENTED
 UNIMPLEMENTED(...)

not yet finished feature

[[FIXME]]
.FIXME
 FIXME(...)

known bug to be fixed later

[[TODO]]
.TODO
 TODO(...)

enhancement to be done soon

[[PLANNED]]
.PLANNED
 PLANNED(...)

future enhancement

[[NOTREACHED]]
.NOTREACHED
 NOTREACHED(...)

used to tag code-path which shall be never executed.

[[ELSE_NOTREACHED]]
.ELSE_NOTREACHED
 ELSE_NOTREACHED(...)

same as `else NOTREACHED()`, but wholly optimized out in release builds.

// doc/annotationtable.txt:1 //

The advantage of this tagging over plain source comments is that we can take
some actions if we run in such a tag at compile or runtime:

the action to be taken when such a macro is hit depends on the build level:

[grid="all"]
`-------------`-----`------------`-----------------------------------------
              ALPHA BETA         RELEASE
---------------------------------------------------------------------------
DEPRECATED    log   nothing      wont compile
UNIMPLEMENTED abort abort        wont compile
FIXME         log   wont compile wont compile
TODO          log   log          wont compile
PLANNED       log   nothing      nothing
NOTREACHED    abort abort        removed
---------------------------------------------------------------------------

Legend:

  * abort means first log and then abort
  * log will only log once for each sourceline (not on each hit)
  * wont compile will abort compilation with a error message
  * nothing optimized out, sane way
  * removed optimized out for performance reasons

// doc/scopechecks.txt:1 //
[[CHECKED]]
Scope Checks
------------
[[UNCHECKED]]

The programmer can tag any scope as `UNCHECKED` or `CHECKED`. In *ALPHA* and *BETA*
builds, a global `UNCHECKED` is implied. In *RELEASE* builds, `UNCHECKED` scopes are
not allowed.

// doc/assertiontable.txt:1 //
.Assertions active depending on Build level and Scope
[grid="all"]
`-----------`-----------------------------------------`-----------------------------`-------------------
            *ALPHA*                                   *BETA*                        *RELEASE*
*UNCHECKED* Preconditions, Postconditions, Invariants Preconditions, Postconditions compiling will abort
*CHECKED*   Preconditions, Postconditions             Preconditions
------------------------------------------------------------------------------------------------------

// src/nobug.h:776 //
Fault injection
---------------

NoBug has some macros which can be used to simulate errorneous behaviour:

[[INJECT_GOODBAD]]
.INJECT_GOODBAD
 INJECT_GOODBAD(expr, good, bad)

substitutes to an expression and returns good when expr is false and
bad when expr is true. In BETA and RELEASE builds 'good' is always returned.

[[INJECT_FAULT]]
.INJECT_FAULT
 INJECT_FAULT(expr, bad)

substitutes to a statement which executes 'bad'
when expr is true. Optimitzed out in BETA and RELEASE builds.

[[INJECT_LEVEL]]
.INJECT_LEVEL
In both cases, when a fault is injected it will be logged at
`NOBUG_INJECT_LEVEL` (default: `LOG_NOTICE`). This can be defined
before including 'nobug.h' to override it.

// doc/resourcetracking.txt:1 //
Resource Tracking
-----------------

With little effort, NoBug can watch all kinds of resources a program uses. This
becomes useful for resources which are distributed over a multithreaded
program. Resource tracking includes logging actions on resource and checking
locking policies over acquired resources. Resource logging is active in ALPHA
and BETA builds when NOBUG_RESOURCE_LOGGING is defined to 1 (the default).
The resource tracker which supervises locking policies is only enabled in
ALPHA builds.

Concepts
~~~~~~~~

Resources are abstracted, NoBug has little knowledge about the semantics of a
resource, it only keeps records of resources and the code using it and ensures
basic constraints. Detailed usage checks of resource have to be done with other
NoBug facilities.

Resources are identified by a arbitrary identifier which is just a
pointer. Additionally a name, the type and the source locations which
announced the resource are stored.

Code which wants to use a resource calls a enter macro with its own identifier
and state, then might alter the state and finally a leave macro when finished
with it.

When a resource is used one has to pass one of this states:

  * NOBUG_RESOURCE_WAITING
      + For resources where acquisition could block (locks) you enter it with a
        WAITING state first and as soon you acquired it you change the state to one
        of the following.
  * NOBUG_RESOURCE_EXCLUSIVE
      + Acquired the resource exclusively. It must not be acquired
        again, not even from the same thread.
  * NOBUG_RESOURCE_RECURSIVE
      + The resource might be entered multiple times from the same
        thread with this state.
  * NOBUG_RESOURCE_SHARED
      + The resource might be entered multiple times from any thread
        with this state.

Possible state transitions:

["graphviz", "resource-transistinons.png"]
---------------------------------------------------------------------
strict digraph G
{
        edge [fontname=Courier fontsize=10]

        start [shape=ellipse]

        node [shape=box]

        start -> Waiting [label="ENTER()"]
        start -> Exclusive [label="ENTER()"]
        start -> Recursive [label="ENTER()"]

        Waiting -> Exclusive [label="STATE()"]
        Waiting -> Recursive [label="STATE()"]

        Recursive -> Recursive [label="ENTER()\nSTATE()"]

        Waiting -> end [label="LEAVE()"]
        Exclusive -> end [label="LEAVE()"]
        Recursive -> end [label="LEAVE()"]

        end [shape=ellipse]
}
---------------------------------------------------------------------

Notes
~~~~~

There are small race conditions between logging and checking resource tracking
and the actual call to the resource using function. This is a design decision
there is no way to account for this exactly when the function call may block.

The Resource Tracker relies on proper announce/forget and enter/leave
are properly pairing. The programmer should ensure that this is done
right, otherwise the results are unpredictable.

// src/nobug.h:993 //
Resource tracking macros
~~~~~~~~~~~~~~~~~~~~~~~~

[[RESOURCE_LOGGING]]
[[RESOURCE_LOG_LEVEL]]

Unless the user defines `NOBUG_RESOURCE_LOGGING` to 0 each of the above macros
will emit a log message at `NOBUG_RESOURCE_LOG_LEVEL` which defaults to
`LOG_DEBUG`.

[[RESOURCE_HANDLE]]
.RESOURCE_HANDLE
 RESOURCE_HANDLE(name)
 RESOURCE_HANDLE_INIT(name)
 RESOURCE_USER(name)
 RESOURCE_USER_INIT(name)

Define and initialize handles for to track resources.

 `name`::
     identifer to be used for the handle

There are two kinds of handles, each resource itself is abstracted with a
`RESOURCE_HANDLE` and every access to this resources is tracked through a
`RESOURCE_USER` handle. These macros takes care that the declaration is optimized
out in the same manner as the rest of the resource tracker would be disabled.
You can still instantiate handles as `struct nobug_resource_record*` or
`struct nobug_resource_user*` in structures which must have a constant size
unconditional of the build level. The two `*_INIT` macros can be used to initialize
resource handles and are optimized out when the resource tracker gets disabled.

[[RESOURCE_ANNOUNCE]]
.RESOURCE_ANNOUNCE
 RESOURCE_ANNOUNCE(flag, type, name, identifier, handle)
 NOBUG_RESOURCE_ANNOUNCE_RAW(flagptr, type, name, ptr, handle)
 NOBUG_RESOURCE_ANNOUNCE_RAW_CTX(flagptr, type, name, ptr, handle, context)

Publishes resources.

 `flag`::
     the NoBug flag name which turns logging on for this macro
 `type`::
     a string which should denote the domain of the resource,
     examples are "file", "mutex", "lock", "database" and so on
 `name`::
     the actual name of a named resource this as string which
     together with type forms a unique identifier of the resource. `type` and
     `name` must be available through the entire lifetime of the resource, using
     literal strings is recommended
 `identifier`::
     a pointer which should be unique for this resource, any
     kind of pointer will suffice, it is only used for identification. In
     multithreaded applications the thread identifier becomes an additional
     identifier
 `handle`::
     a `NOBUG_RESOURCE_HANDLE` which will be initialized to point to
     the newly created resource.

Resources must be unique, it is a fatal error when a resource it tried to be
announced more than one time.

[[RESOURCE_FORGET]]
.RESOURCE_FORGET
 RESOURCE_FORGET(flag, handle)
 NOBUG_RESOURCE_FORGET_RAW(flagptr, handle)
 NOBUG_RESOURCE_FORGET_RAW_CTX(flagptr, handle, context)

Removes resources that have become unavailable from the registry.

`flag`::
    the NoBug flag which turns logging on for this macro
`handle`::
    the `NOBUG_RESOURCE_HANDLE` used to track this resource

The resource must still exist and no users must be attached to it, else a fatal
error is raised.

[[RESOURCE_ENTER]]
.RESOURCE_ENTER
 RESOURCE_ENTER(flag, announced, user, state, handle)
 NOBUG_RESOURCE_ENTER_CTX(flag, resource, user, state, handle, context)

Acquire a resource.

`flag`::
    nobug flag which turns logging on for this macro
`announced`::
    the handle set by `RESOURCE_ANNOUNCE`
`user`::
    a free-form identifier
`state`::
    the initial state, one of `NOBUG_RESOURCE_WAITING`, `NOBUG_RESOURCE_TRYING`,
    `NOBUG_RESOURCE_EXCLUSIVE`, `NOBUG_RESOURCE_RECURSIVE` or `NOBUG_RESOURCE_SHARED`
`handle`::
    a `NOBUG_RESOURCE_HANDLE` which will be initialized to the
    entering node

[[RESOURCE_WAIT]]
.RESOURCE_WAIT
 RESOURCE_WAIT(flag, resource, user, handle)
 NOBUG_RESOURCE_WAIT_CTX(flag, resource, user, handle, context)

This is just an alias for RESOURCE_ENTER(flag, resource, user, NOBUG_RESOURCE_WAITING, handle)

.How to use it
[source,c]
----
RESOURCE_WAIT(flag, resource, user, handle);
if (lock_my_resource() == ERROR)
  NOBUG_RESOURCE_LEAVE(flag, handle);
else
  RESOURCE_STATE(flag, NOBUG_RESOURCE_EXCLUSIVE, handle);
----

[[RESOURCE_TRY]]
.RESOURCE_TRY
 RESOURCE_TRY(flag, resource, user, handle)
 NOBUG_RESOURCE_TRY_CTX(flag, resource, user, handle, context)

This is just an alias for RESOURCE_ENTER(flag, resource, user, NOBUG_RESOURCE_TRYING, handle).
Trying on a resource is similar to waiting but will not trigger a deadlock check. This can be used
when a deadlock is expected at runtime and one handles this otherwise (by a timed wait or something like that).

[[RESOURCE_STATE]]
.RESOURCE_STATE
 RESOURCE_STATE(flag, entered, state)
 NOBUG_RESOURCE_STATE_CTX(flag, state, entered, context)
 NOBUG_RESOURCE_STATE_RAW(flagptr, state, entered)
 NOBUG_RESOURCE_STATE_RAW_CTX(flagptr, nstate, entered, context)

Changes resource's state.

`flag`::
    is nobug flag which turns logging on for this macro
`state`::
    the new state Note that only certain state transitions are
    allowed, see discussion/diagram above
`entered`::
    the handle set by `RESOURCE_ENTER`

[[RESOURCE_LEAVE]]
.RESOURCE_LEAVE
 RESOURCE_LEAVE(flag, handle){}
 NOBUG_RESOURCE_LEAVE_RAW(flagptr, handle){}
 NOBUG_RESOURCE_LEAVE_RAW_CTX(flagptr, handle, context){}

Disconnect from a resource identified with its handle.

`flag`::
    nobug flag which turns logging on for this macro
`handle`::
    the handle you got while entering the resource

'RESOURCE_LEAVE()' acts like the head of a C loop statement, it ties to the following
(block-) statement. Leaving and the user defined following statement are atomic.
This statement must not be left by break, return or any other kind of jump. NoBug does
not assert this (for for Performance reasons).

.How to use it
[source,c]
----
NOBUG_RESOURCE_LEAVE(flag, handle)
  {
    unlock_my_resource();
  }
----

[[RESOURCE_ASSERT_STATE]]
.RESOURCE_ASSERT_STATE
 RESOURCE_ASSERT_STATE(resource, state)
 RESOURCE_ASSERT_STATE_IF(when, resource, state)
 NOBUG_RESOURCE_ASSERT_STATE_CTX(resource, state, context)
 NOBUG_RESOURCE_ASSERT_STATE_IF_CTX(when, resource, state, context)

Assert that we have a resource in a given state. For multithreaded programms the topmost
state of the calling thread is checked, for non threadeded programs the most recent state on
resource is used.

`when`::
    Condition which must be true for testing the assertion
`resource`::
    Resource handle
`state`::
    The expected state

[[RESOURCE_DUMP]]
.RESOURCE_DUMP
 NOBUG_RESOURCE_DUMP(flag, handle)
 NOBUG_RESOURCE_DUMP_IF(when, flag, handle)

Dump the state of a single resource.

`when`::
    Condition which must be true to dump the resource
`flag`::
    Nobug flag for the log channel
`handle`::
    handle of the resource to be dumped

[[RESOURCE_DUMPALL]]
.RESOURCE_DUMPALL
 NOBUG_RESOURCE_DUMPALL(flag)
 NOBUG_RESOURCE_DUMPALL_IF(when, flag)

Dump the state of all resources.

`when`::
    Condition which must be true to dump the resources
`flag`::
    Nobug flag for the log channel

[[RESOURCE_LIST]]
.RESOURCE_LIST
 NOBUG_RESOURCE_LIST(flag)
 NOBUG_RESOURCE_LIST_IF(when, flag)

List all registered resources.

`when`::
    Condition which must be true to list the resources
`flag`::
    Nobug flag for the log channel

// doc/resourceexample.txt:1 //
.How to use the Resourcetracker
[source,c]
----
NOBUG_DEFINE_FLAG_LIMIT(test, LOG_DEBUG);

void example()
{
  // define a mutex and announce it
  pthread_mutex_t my_mutex = PTHREAD_MUTEX_INITIALIZER;
  RESOURCE_HANDLE(resource);

  // 'example' is just a pointer to this function which suffices as unique id
  RESOURCE_ANNOUNCE(test, "mutex", "my_mutex", example, resource);

  // the following would be done in a different thread in a real program
  // define a handle
  RESOURCE_HANDLE(enter);

  // announce that we want to use the resource
  // &enter also suffices as unique pointer, which is all we need as identifer here
  RESOURCE_WAIT(flag, resource, &enter, enter)
    {
      // lock() might block
      pthread_mutex_lock (&my_mutex);
      // assume no errors, got it, change the state
      RESOURCE_STATE(test, NOBUG_RESOURCE_EXCLUSIVE, enter);
    }

  ////////////////////////////////////////
  // program does something useful here //
  ////////////////////////////////////////

  // we don't need it anymore
  RESOURCE_LEAVE(test, enter)  // << no semicolon
    pthread_mutex_unlock (&my_mutex);

  // back in the main thread
  RESOURCE_FORGET(test, resource);                         // remove the resource from the public registry
}
----

// doc/resourcedeadlock.txt:1 //
Deadlock Detection
~~~~~~~~~~~~~~~~~~

The Resource Tracker is able to detect potential deadlocks. This is done by
learning the relations between locks (precedence). A possible deadlock results
in a log message and a fatal abort. Note that only waiting on resources can
lead to a deadlock. Deadlock detection is implemented in the Resource Tracker
and active in ALPHA builds and optimized out on any other build level.

For details about the deadlock detection algorithm see
xref:deadlock_detection[Appendix: Resource Tracking Alorithm].

// src/nobug.h:2331 //
Callbacks
---------

NoBug provides callbacks, applications can use these
to present logging information in some custom way or hook some special processing in.
The callbacks are initialized to NULL and never modified by NoBug, its the solve responsibility
of the user to manage them.

CAUTION: There are certain constraints what and what not can be done in callbacks
         documented below which must be followed.

[[logging_cb]]
.type of logging callbacks
 typedef void (*nobug_logging_cb)(const struct nobug_flag* flag, int priority, const char *log, void* data)

used for the logging callbacks

 `flag`::
    Flag structure which defines the logging configuration for this event
 `priority`::
    Log level of the current event
 `log`::
    Pointing to the current log line in the ringbuffer or `NULL`
 `data`::
    Global pointer defined by the user, passed arround (see below)

[[abort_cb]]
.type of abort callback
 typedef void (*nobug_abort_cb)(void* data)

used for the abort callback

 `data`::
    Global data defined by the user, passed arround (see below)

[[callback_data]]
.passing data to callbacks
 void* nobug_callback_data

This global variable is initialized to `NULL` and will never be touched by NoBug. One can use it
to pass extra data to the callback functions.

[[logging_callback]]
.callback when logging
 nobug_logging_cb nobug_logging_callback

This callback gets called when something gets logged.
NoBug will still hold its mutexes when calling this hook, calling NoBug logging or resource tracking
functions from here recursively will deadlock and must be avoided.
The `log` parameter points to the logging message in the ringbuffer.
Unlike other logging targets it is not automatically limited to the log level configured
in the flag but called unconditionally. The callback should implement its own limiting.

When one wants to do complex calls which may include recursion into logging and resource tracking
functions, the intended way is to pass contextual information possibly including a __copy__ of the
`log` parameter in xref:THREAD_DATA[NOBUG_THREAD_DATA] to the postlogging callback (see below).
Other internal NoBug facilties, like the ringbuffer etc, are protected by the mutexes and may be accessed
from this function.

[[postlogging_callback]]
.callback after logging
 nobug_logging_cb nobug_postlogging_callback

This callback gets called after something got logged. The `log` parameter is always NULL and all
NoBug mutexes are released. This means that this function may call any complex things, including
calling logging and resource tracking, but may not call internal NoBug facilities.
Contextual created in the `nobug_logging_callback` and stored in xref:THREAD_DATA[NOBUG_THREAD_DATA] can be
retrieved here and may need to be cleaned up here.

[[abort_callback]]
.callback for aborting
 nobug_abort_cb nobug_abort_callback

This callback gets called when the application shall be terminated due an error.
It can be used to hook exceptions or similar things in. When it returns, `abort()`
is called.

IMPORTANT: Errors detected by NoBug are always fatal. If one handles and possible
           throws an exception here, the application must shut down as soon as possible.
           Most causes for aborts are optimitzed out in `RELEASE` builds.

// src/nobug.h:1552 //
Tool Macros
-----------

[[NOBUG_FLAG_RAW]]
.NOBUG_FLAG_RAW
 NOBUG_FLAG_RAW(ptr)

Using this macro one can pass a direct pointer to a flag where a name would
be expected. This is sometimes convinient when flag pointers are passed around
in management strutures and one wants to tie logging to dynamic targets.

[source,c]
----
NOBUG_DEFINE_FLAG(myflag);
...
struct nobug_flag* ptr = &NOBUG_FLAG(myflag);
TRACE(NOBUG_FLAG_RAW(ptr), "Passed flag by pointer")
----

[[BACKTRACE]]
.Backtraces
 BACKTRACE
 NOBUG_BACKTRACE_CTX(context)

The backtrace macro logs a stacktrace using the NoBug facilities.
This is automatically called when NoBug finds an error and is due
to abort. But one might call it manually too.

[[ABORT]]
.Aborting
 NOBUG_ABORT_

This is the default implementation for aborting the program, it first syncs all ringbuffers to disk, then
calls the abort callback if defined and then `abort()`.

 NOBUG_ABORT

If not overridden, evaluates to `NOBUG_ABORT_`. One can override this before including
`nobug.h` to customize abortion behaviour. This will be local to the translation unit then.

[[NOBUG_ALPHA_COMMA]]
.NOBUG_ALPHA_COMMA
 NOBUG_ALPHA_COMMA(something)
 NOBUG_ALPHA_COMMA_NULL

Sometimes it is useful to have initializer code only in *ALPHA* builds, for example when you
conditionally include resource handles only in *ALPHA* versions. An initializer can then
use this macros to append a comman and something else only in *ALPHA* builds as in:
 struct foo = {"foo", "bar" NOBUG_ALPHA_COMMA_NULL };

[[NOBUG_IF]]
.NOBUG_IF_*
 NOBUG_IF_ALPHA(...)
 NOBUG_IF_NOT_ALPHA(...)
 NOBUG_IF_BETA(...)
 NOBUG_IF_NOT_BETA(...)
 NOBUG_IF_RELEASE(...)
 NOBUG_IF_NOT_RELEASE(...)

This macros allow one to conditionally include the code in '(...)' only if the
criteria on the build level is met. If not, nothing gets substituted. Mostly used
internally, but can also be used for custom things.

// doc/multithreading.txt:1 //
[[multithreading]]
Multithreading
--------------

It is important that NoBug protects certain operations with locks in
multithreaded programs. You have to ensure that 'HAVE_PTHREAD_H' is defined by
the configuration system and use the 'libnobugmt' library for linking. It is
particular important that libraries using NoBug are compiled with
'HAVE_PTHREAD_H' enabled when they are intended to be used in multithreaded
programs.

When Multithreading is used, log messages contain a identifier of the
originating thread. This identifier should be set by

[[THREAD_ID_SET]]
.NOBUG_THREAD_ID_SET
 NOBUG_THREAD_ID_SET(name)

`name`::
        New name for the thread

Nobug will assemble a unique identifier by appending a underscore and a
number to name, for example `NOBUG_THREAD_ID_SET("gui")` will result in a
identifier like "gui_5". When you don't set a thread identifier, then NoBug
assigns one automatically with the name 'thread' preprended if needed. Thread
identifiers may be reset with a new call to this macro.

[[THREAD_ID_GET]]
.NOBUG_THREAD_ID_GET
 NOBUG_THREAD_ID_GET

Will return a const char* of the thread id in multithreaded programs and
a pointer to a literal empty string in singlethreaded programs.

[[THREAD_DATA]]
.NOBUG_THREAD_DATA
 NOBUG_THREAD_DATA

Evaluates to a variable of type `void*` which can be used to store
thread local information. This is useable for xref:_callbacks[callbacks] which may
prepare context information to be reused later.

This macro is also available in singlethreaded programs, refering to a
single global variable.

Nobug initializes this variable to `NULL` and then touches it never again.

// src/nobug_rbdump.c:33 //
[[rbdump]]
Dumping Persistent Ringbuffers
------------------------------

NoBug installs the `nobug_rbdump` tool for dumping the content of a persistent
ringbuffer. It is invoked with the filename of the ringbuffer, the content is then
printed to stdout.

// doc/testsuite.txt:1 //
Testsuite
---------

 TODO Documentation to be written, use the source Luke!

NoBug maintains a `test.sh` script which drives extensive testsuites.
Look at into the 'tests/' folder about how to apply this.

// doc/bestpractices.txt:1 //
Best Practices
--------------

NOTE: this section is very work in progress

.Workflow

 1. Development
      * Write a testsuite, build your program with -O0 -g -DEBUG_ALPHA and run
        the testsuite under valgrind control. Hack until the program mets the
        specifications defined by the testsuite.
 2. Beta Test
      * Build with desired optimization level and -g -DEBUG_BETA and give the
        program to your beta testers.
 3. Release
      * Build it with optimization and without -g -DEBUG_*

.What and when to check

  * Add REQUIRE checks on your interfaces (incoming parameters). Especially if
    a argument might not cover the whole range of the underlying type.
  * Don't waste your and your CPU's time with unnecessary checks. The testsuite
    should validate your program. NoBug aids in debugging. You can add
    Postconditions (ENSURE) and Invariants when you have a bug somewhere and
    want to nail it down.
  * Added checks don't need to be removed.
  * When you use the CHECKED/UNCHECKED features then don't forget C scoping
    rules, tag things as CHECKED from the leaves to the root.

.Tips & Tricks

  * TRACE(flagname) at the begin of every nontrivial function will easily log
    the progress of your application.
  * Trying a RELEASE build will abort on certain conditions (known BUG, TODO's,
    UNCHECKED code), you can use this to find these spots.

Appendix
--------

// src/nobug_resources.c:306 //
[[deadlock_detection]]
The Resource Tracking Algorithm
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Each resource registers a global 'resource_record'.

Every new locking path discovered is stored as 'resource_node' structures which refer to the associated
'resource_record'.

Threads keep a trail of 'resource_user' strcutures for each resource entered. This 'resource_user' struct
refer to the 'resource_nodes' and thus indirectly to the associated 'resource_record'.

The deadlock checker uses this information to test if the acqusition of a new resource would yield a
potential deadlock.

[[nobug_resource_enter]]
Entering Resources
^^^^^^^^^^^^^^^^^^

In multithreaded programs, whenever a thread wants to wait for a 'resource_record'
the deadlock checker jumps in.

The deadlock checking algorithm is anticipatory as it will find and abort on conditions which may lead
to a potential deadlock by violating the locking order learned earlier.

Each thread holds a stack (list) of each 'resource_user' it created. Leaving
a resource will remove it from this stacklist.

Each 'resource_record' stores the trail which other 'resource_records' are already entered. This relations
are implemented with the 'resource_node' helper structure.

////
TODO: insert diagram here
  2-3
1
  3-4-2

1-3-2-4

3-4-2

1-4-2

////

First we find out if there is already a node from the to be acquired resource back to
the topmost node of the current threads user stack.

[source,c]
---------------------------------------------------------------------
  struct nobug_resource_user* user = NULL;
  struct nobug_resource_node* node = NULL;

  if (!llist_is_empty (&tls->res_stack))
    {
      user = LLIST_TO_STRUCTP (llist_tail (&tls->res_stack),
                               struct nobug_resource_user,
                               res_stack);

      struct nobug_resource_node templ =
        {
         ...
          user->current->resource,
         ...
        };

      node = (struct nobug_resource_node*)
        llist_ufind (&resource->nodes,
                     &templ.node,
                     nobug_resource_node_resource_cmpfn,
                     NULL);
    }
  ...
---------------------------------------------------------------------

Deadlock checking is only done when the node is entered in `WAITING` state and only
available in multithreaded programs.

[source,c]
---------------------------------------------------------------------
  if (state == NOBUG_RESOURCE_WAITING)
    {
#if NOBUG_USE_PTHREAD
      ...
---------------------------------------------------------------------

If node was found above, then this locking path is already validated and no deadlock can happen,
else, if this stack already holds a resource (user is set) we have to go on with checking.

[source,c]
---------------------------------------------------------------------
      if (!node && user)
        {
          ...
---------------------------------------------------------------------

If not then its checked that the resource to be entered is not on any parent trail of the current topmost resource,
if it is then this could be a deadlock which needs to be further investigated.

[source,c]
---------------------------------------------------------------------
          LLIST_FOREACH (&user->current->resource->nodes, n)
            {
              for (struct nobug_resource_node* itr =
                     ((struct nobug_resource_node*)n)->parent;
                   itr;
                   itr = itr->parent)
                {
                  if (itr->resource == resource)
                    {
                      ...
---------------------------------------------------------------------

if the resource was on the trail, we search if there is a common ancestor before the resource
on the trail and the threads current chain,
if yes then this ancestor protects against deadlocks and we can continue.

[source,c]
---------------------------------------------------------------------
                      for (struct nobug_resource_node* itr2 = itr->parent;
                           itr2;
                           itr2 = itr2->parent)
                        {
                          LLIST_FOREACH_REV (&tls->res_stack, p)
                            {
                              struct nobug_resource_user* user =
                                LLIST_TO_STRUCTP (p,
                                                  struct nobug_resource_user,
                                                  res_stack);
                              if (user->current->resource == itr2->resource)
                                goto done;
                            }
---------------------------------------------------------------------

If no ancestor found, we finally abort with a potential deadlock condition.

[source,c]
---------------------------------------------------------------------
                          nobug_resource_error = "possible deadlock detected";
                          return NULL;
                          ...
---------------------------------------------------------------------


[[nobug_resource_leave]]
Leaving Resources
^^^^^^^^^^^^^^^^^

store the tail and next aside, we need it later

[source,c]
---------------------------------------------------------------------
#if NOBUG_USE_PTHREAD
      struct nobug_resource_user* tail =
        LLIST_TO_STRUCTP (llist_tail (&user->thread->res_stack),
                          struct nobug_resource_user,
                          res_stack);
      struct nobug_resource_user* next =
        LLIST_TO_STRUCTP (llist_next (&user->res_stack),
                          struct nobug_resource_user,
                          res_stack);
---------------------------------------------------------------------

remove user struct from thread stack
The res_stack is now like it is supposed to look like with the 'user' removed.
We now need to fix the node tree up to match this list.

[source,c]
---------------------------------------------------------------------
      llist_unlink_fast_ (&user->res_stack);
---------------------------------------------------------------------

When the the user node was not the tail or only node of the thread stack, we have to check
(and possibly construct) a new node chain for it. No valdation of this chain needs to be done,
since it was already validated when entering the resources first.

[source,c]
---------------------------------------------------------------------
      if (user != tail && !llist_is_empty (&user->thread->res_stack))
        {
          struct nobug_resource_user* parent = NULL;
          if (llist_head (&user->thread->res_stack) != &next->res_stack)
            {
              parent =
                LLIST_TO_STRUCTP (llist_prev (&next->res_stack),
                                  struct nobug_resource_user,
                                  res_stack);
            }
---------------------------------------------------------------------

iterate over all users following the removed node, finding nodes pointing to this users or
create new nodes.

[source,c]
---------------------------------------------------------------------
          LLIST_FORRANGE (&next->res_stack, &user->thread->res_stack, n)
            {
              struct nobug_resource_user* cur =
                LLIST_TO_STRUCTP (n,
                                  struct nobug_resource_user,
                                  res_stack);

---------------------------------------------------------------------
// src/nobug_resources.c:655 //

find the node pointing back to parent, create a new one if not found, rinse repeat

[source,c]
---------------------------------------------------------------------
              struct nobug_resource_node templ =
                {
                  ...
                  NULL,
                  ...
                };

              struct nobug_resource_node* node = (struct nobug_resource_node*)
                llist_ufind (&resource->nodes,
                             &templ.node,
                             nobug_resource_node_parent_cmpfn,
                             NULL);

              if (!node)
                {
                  node = nobug_resource_node_new (resource,
                                                  parent?parent->current:NULL);
                  if (!node)
                    {
                      nobug_resource_error = "internal allocation error";
                      return 0;
                    }
                }

              parent = cur;
            }
        }
---------------------------------------------------------------------


Index
-----

xref:ABORT[Aborting]:: abort the program
xref:abort_callback[callback for aborting]:: hook to handle a termination
xref:abort_cb[type of abort callback]:: type of a abort callback function
xref:ALERT[ALERT]:: about to die
xref:ASSERT[ASSERT]:: generic assertion
xref:assert[assert]:: C standard assertion
xref:BACKTRACE[Backtraces]:: generate a backtrace
xref:buildlevel[Build Levels]:: selecting the build level
xref:callback_data[passing data to callbacks]:: data to be passed to callbacks
xref:CHECK[CHECK]:: unnconditional assertion for testsuites
xref:CHECKED[CHECKED, Scope]:: tag scope as reviewed
xref:Cplusplus_logflags[C++ support, C++ logflags]:: C++ support for log flags
xref:CRITICAL[CRITICAL]:: can not continue
xref:deadlock_detection[The Resource Tracking Algorithm]:: how resources are tracked
xref:DECLARE_FLAG[DECLARE_FLAG]:: declaring a flag
xref:DECLARE_ONLY[DECLARE_ONLY]:: force flag declarations only
xref:DEFINE_FLAG[DEFINE_FLAG]:: defining a flag
xref:DEFINE_FLAG_LIMIT[DEFINE_FLAG_LIMIT]:: defining a flag w/ log limit
xref:DEFINE_FLAG_PARENT[DEFINE_FLAG_PARENT]:: defining a flag hierarchy
xref:DEFINE_FLAG_PARENT_LIMIT[DEFINE_FLAG_PARENT_LIMIT]:: defining a flag hierarchy, w/ log limit
xref:DEPRECATED[DEPRECATED]:: to be discarded in future
xref:DUMP[DUMP]:: dumping datastructures
xref:DUMP_LOG[DUMP_LOG]:: logging helper for dumping
xref:ECHO[ECHO]:: unconditional logging for tests
xref:ELSE_NOTREACHED[ELSE_NOTREACHED]:: alternative never taken
xref:ENSURE[ENSURE]:: postconditions (computation outcomes)
xref:ERROR[ERROR]:: something gone wrong
xref:FIXME[FIXME]:: known bug
xref:INFO[INFO]:: progress message
xref:INJECT_FAULT[INJECT_FAULT]:: fault injection statement
xref:INJECT_GOODBAD[INJECT_GOODBAD]:: fault injection expression
xref:INJECT_LEVEL[INJECT_LEVEL]:: log level for fault injection
xref:INVARIANT[INVARIANT]:: validate invariant state
xref:LOG[LOG]:: generic logging
xref:LOG_BASELIMIT[LOG_BASELIMIT]:: minimum compliled-in logging limit
xref:logflags[Log Flags]:: define hierarchies for logging output
xref:logging_callback[callback when logging]:: hook when something get logged
xref:logging_cb[type of logging callbacks]:: type of a logging callback function
xref:multithreading[Multithreading]:: using NoBug in multithreaded programs
xref:NOBUG_ALPHA_COMMA[NOBUG_ALPHA_COMMA]:: append something after a comma in *ALPHA* builds
xref:NOBUG_ANN[NOBUG_ANN]:: log flag for annotations
xref:NOBUG_CONTEXT[Source Contexts]:: pass information about the source location
xref:NOBUG_ENV[Control what gets logged]:: environment variable for loging control
xref:nobug_flag[nobug (flag)]:: log flag used to show nobug actions
xref:NOBUG_FLAG_RAW[NOBUG_FLAG_RAW]:: pass direct flag pointer
xref:NOBUG_IF[NOBUG_IF_*]:: include code conditionally on build level
xref:NOBUG_ON[NOBUG_ON]:: log flag which is always enabled
xref:nobug_resource_enter[Entering Resources]:: deadlock check on enter
xref:nobug_resource_leave[Leaving Resources]:: fix resource lists
xref:NOTICE[NOTICE]:: detailed progress message
xref:NOTREACHED[NOTREACHED]:: code path never taken
xref:PLANNED[PLANNED]:: ideas for future
xref:postlogging_callback[callback after logging]:: hook after something get logged
xref:rbdump[Dumping Persistent Ringbuffers]:: dumping persistent ringbuffers
xref:REQUIRE[REQUIRE]:: preconditions (input parameters)
xref:RESOURCE_ANNOUNCE[RESOURCE_ANNOUNCE]:: publish new resources
xref:RESOURCE_ASSERT_STATE[RESOURCE_ASSERT_STATE]:: assert the state of a resource
xref:RESOURCE_DUMP[RESOURCE_DUMP]:: dump the state of a single resource
xref:RESOURCE_DUMPALL[RESOURCE_DUMPALL]:: dump the state of all resources
xref:RESOURCE_ENTER[RESOURCE_ENTER]:: claim a resource
xref:RESOURCE_FORGET[RESOURCE_FORGET]:: remove resources
xref:RESOURCE_HANDLE[RESOURCE_HANDLE]:: define resource handles
xref:RESOURCE_LEAVE[RESOURCE_LEAVE]:: relinquish a claimed resource
xref:RESOURCE_LIST[RESOURCE_LIST]:: enumerate all registered resources
xref:RESOURCE_LOG_LEVEL[RESOURCE_LOG_LEVEL]:: select the log level for resource logging
xref:RESOURCE_LOGGING[RESOURCE_LOGGING]:: switch resource logging on and off
xref:RESOURCE_STATE[RESOURCE_STATE]:: change the state of a resource
xref:RESOURCE_TRY[RESOURCE_TRY]:: wait for a resource to become available
xref:RESOURCE_WAIT[RESOURCE_WAIT]:: wait for a resource to become available
xref:THREAD_DATA[NOBUG_THREAD_DATA]:: thread local data for application use
xref:THREAD_ID_GET[NOBUG_THREAD_ID_GET]:: query thread id
xref:THREAD_ID_SET[NOBUG_THREAD_ID_SET]:: set or reset thread id
xref:TODO[TODO]:: things to be done
xref:TRACE[TRACE]:: debugging level message
xref:UNCHECKED[UNCHECKED, Scope]:: tag scope as unreviewed
xref:UNIMPLEMENTED[UNIMPLEMENTED]:: not yet implemented
xref:WARN[WARN]:: unexpected fixable error

// doc/license.txt:1 //
License
-------

    NoBug
    Copyright (C) 2009          Christian Thäter <ct@pipapo.org>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with this program; if not, write to the Free Software Foundation, Inc.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

.License Rationale

NoBug is released under the "GNU General Public License version 2 or
any later" to protect its freedom. If one wants to use NoBug in a
propietary program, please contact the main author for
acknowledging relicensing terms.

For BSD license style Free Software, this means you can not distribute
binaries linking NoBug without making its source available. To make
this compatible, it is suggested that you dual-license your software
with your prefered BSD like license and the GPL. As long as it uses
NoBug, the GPL will take over and you have to make the source
available, while one can ship a BSD or LGPL Licensed headerfile which
defines all NoBug macros as empty macros and remove libnobug from the
linking, then NoBug isn't used anymore and you may apply BSD license
terms for resulting binaries.


Contributor Agreement
~~~~~~~~~~~~~~~~~~~~~

Improvements and patches must be licensed as "GPL v2 or any later" to
be acceptable. Further a contributor must either assign his copyright
to the main NoBug author or agree with the possibility that NoBug can
be relicensed for propietary use:

 Independent of the GPL license as stated above, The main author of
 NoBug explicitly reserve the right to relicense NoBug under
 different, even propietary terms. Any contributor agrees to such
 a possiblility by sending his contribution to be included into
 the official releases.

 This agreement is bilateral, every contributor who worked on a
 substantial part of NoBug has the right to relicense it after
 negotiation with the NoBug main author. Exact terms of such
 relicensing are worked out on a per case base.

The intention is that anyone who worked on NoBug should be able to
benefit from his work. This means one should be able to use it at his
workplace, to gain a job or as well as relicense it for a customer.
Unlike other projects which simply ask for transfering the copyright
to the main author, NoBug tries to make it possible to retain the
copyright by anyone who helped the project.

This additional agreement has no impact on the GPL, it's sole purpose
is to define relicensing policies between the NoBug main author and
contributors. When you recieve NoBug it will be licensed under
GPL unless you personally acknowledged other terms with the NoBug main
author (or any other main contributor).

If anyone feels he is not credited in the 'AUTHORS' file or in any
copyright notice, please contact the main author for inclusion.