Doc/lib/libresource.tex

   1 \section{\module{resource} ---
   2          Resource usage information}
   3
   4 \declaremodule{builtin}{resource}
   5   \platform{Unix}
   6 \modulesynopsis{An interface to provide resource usage information on
   7   the current process.}
   8 \moduleauthor{Jeremy Hylton}{jeremy@alum.mit.edu}
   9 \sectionauthor{Jeremy Hylton}{jeremy@alum.mit.edu}
  10
  11
  12 This module provides basic mechanisms for measuring and controlling
  13 system resources utilized by a program.
  14
  15 Symbolic constants are used to specify particular system resources and
  16 to request usage information about either the current process or its
  17 children.
  18
  19 A single exception is defined for errors:
  20
  21
  22 \begin{excdesc}{error}
  23   The functions described below may raise this error if the underlying
  24   system call failures unexpectedly.
  25 \end{excdesc}
  26
  27 \subsection{Resource Limits}
  28
  29 Resources usage can be limited using the \function{setrlimit()} function
  30 described below. Each resource is controlled by a pair of limits: a
  31 soft limit and a hard limit. The soft limit is the current limit, and
  32 may be lowered or raised by a process over time. The soft limit can
  33 never exceed the hard limit. The hard limit can be lowered to any
  34 value greater than the soft limit, but not raised. (Only processes with
  35 the effective UID of the super-user can raise a hard limit.)
  36
  37 The specific resources that can be limited are system dependent. They
  38 are described in the \manpage{getrlimit}{2} man page.  The resources
  39 listed below are supported when the underlying operating system
  40 supports them; resources which cannot be checked or controlled by the
  41 operating system are not defined in this module for those platforms.
  42
  43 \begin{funcdesc}{getrlimit}{resource}
  44   Returns a tuple \code{(\var{soft}, \var{hard})} with the current
  45   soft and hard limits of \var{resource}. Raises \exception{ValueError} if
  46   an invalid resource is specified, or \exception{error} if the
  47   underlying system call fails unexpectedly.
  48 \end{funcdesc}
  49
  50 \begin{funcdesc}{setrlimit}{resource, limits}
  51   Sets new limits of consumption of \var{resource}. The \var{limits}
  52   argument must be a tuple \code{(\var{soft}, \var{hard})} of two
  53   integers describing the new limits. A value of \code{-1} can be used to
  54   specify the maximum possible upper limit.
  55
  56   Raises \exception{ValueError} if an invalid resource is specified,
  57   if the new soft limit exceeds the hard limit, or if a process tries
  58   to raise its hard limit (unless the process has an effective UID of
  59   super-user).  Can also raise \exception{error} if the underlying
  60   system call fails.
  61 \end{funcdesc}
  62
  63 These symbols define resources whose consumption can be controlled
  64 using the \function{setrlimit()} and \function{getrlimit()} functions
  65 described below. The values of these symbols are exactly the constants
  66 used by \C{} programs.
  67
  68 The \UNIX{} man page for \manpage{getrlimit}{2} lists the available
  69 resources.  Note that not all systems use the same symbol or same
  70 value to denote the same resource.  This module does not attempt to
  71 mask platform differences --- symbols not defined for a platform will
  72 not be available from this module on that platform.
  73
  74 \begin{datadesc}{RLIMIT_CORE}
  75   The maximum size (in bytes) of a core file that the current process
  76   can create.  This may result in the creation of a partial core file
  77   if a larger core would be required to contain the entire process
  78   image.
  79 \end{datadesc}
  80
  81 \begin{datadesc}{RLIMIT_CPU}
  82   The maximum amount of processor time (in seconds) that a process can
  83   use. If this limit is exceeded, a \constant{SIGXCPU} signal is sent to
  84   the process. (See the \refmodule{signal} module documentation for
  85   information about how to catch this signal and do something useful,
  86   e.g. flush open files to disk.)
  87 \end{datadesc}
  88
  89 \begin{datadesc}{RLIMIT_FSIZE}
  90   The maximum size of a file which the process may create.  This only
  91   affects the stack of the main thread in a multi-threaded process.
  92 \end{datadesc}
  93
  94 \begin{datadesc}{RLIMIT_DATA}
  95   The maximum size (in bytes) of the process's heap.
  96 \end{datadesc}
  97
  98 \begin{datadesc}{RLIMIT_STACK}
  99   The maximum size (in bytes) of the call stack for the current
 100   process.
 101 \end{datadesc}
 102
 103 \begin{datadesc}{RLIMIT_RSS}
 104   The maximum resident set size that should be made available to the
 105   process.
 106 \end{datadesc}
 107
 108 \begin{datadesc}{RLIMIT_NPROC}
 109   The maximum number of processes the current process may create.
 110 \end{datadesc}
 111
 112 \begin{datadesc}{RLIMIT_NOFILE}
 113   The maximum number of open file descriptors for the current
 114   process.
 115 \end{datadesc}
 116
 117 \begin{datadesc}{RLIMIT_OFILE}
 118   The BSD name for \constant{RLIMIT_NOFILE}.
 119 \end{datadesc}
 120
 121 \begin{datadesc}{RLIMIT_MEMLOCK}
 122   The maximum address space which may be locked in memory.
 123 \end{datadesc}
 124
 125 \begin{datadesc}{RLIMIT_VMEM}
 126   The largest area of mapped memory which the process may occupy.
 127 \end{datadesc}
 128
 129 \begin{datadesc}{RLIMIT_AS}
 130   The maximum area (in bytes) of address space which may be taken by
 131   the process.
 132 \end{datadesc}
 133
 134 \subsection{Resource Usage}
 135
 136 These functions are used to retrieve resource usage information:
 137
 138 \begin{funcdesc}{getrusage}{who}
 139   This function returns an object that describes the resources
 140   consumed by either the current process or its children, as specified
 141   by the \var{who} parameter.  The \var{who} parameter should be
 142   specified using one of the \constant{RUSAGE_*} constants described
 143   below.
 144
 145   The fields of the return value each describe how a particular system
 146   resource has been used, e.g. amount of time spent running is user mode
 147   or number of times the process was swapped out of main memory. Some
 148   values are dependent on the clock tick internal, e.g. the amount of
 149   memory the process is using.
 150
 151   For backward compatibility, the return value is also accessible as
 152   a tuple of 16 elements.
 153
 154   The fields \member{ru_utime} and \member{ru_stime} of the return value
 155   are floating point values representing the amount of time spent
 156   executing in user mode and the amount of time spent executing in system
 157   mode, respectively. The remaining values are integers. Consult the
 158   \manpage{getrusage}{2} man page for detailed information about these
 159   values. A brief summary is presented here:
 160
 161 \begin{tableiii}{r|l|l}{code}{Index}{Field}{Resource}
 162   \lineiii{0}{\member{ru_utime}}{time in user mode (float)}
 163   \lineiii{1}{\member{ru_stime}}{time in system mode (float)}
 164   \lineiii{2}{\member{ru_maxrss}}{maximum resident set size}
 165   \lineiii{3}{\member{ru_ixrss}}{shared memory size}
 166   \lineiii{4}{\member{ru_idrss}}{unshared memory size}
 167   \lineiii{5}{\member{ru_isrss}}{unshared stack size}
 168   \lineiii{6}{\member{ru_minflt}}{page faults not requiring I/O}
 169   \lineiii{7}{\member{ru_majflt}}{page faults requiring I/O}
 170   \lineiii{8}{\member{ru_nswap}}{number of swap outs}
 171   \lineiii{9}{\member{ru_inblock}}{block input operations}
 172   \lineiii{10}{\member{ru_oublock}}{block output operations}
 173   \lineiii{11}{\member{ru_msgsnd}}{messages sent}
 174   \lineiii{12}{\member{ru_msgrcv}}{messages received}
 175   \lineiii{13}{\member{ru_nsignals}}{signals received}
 176   \lineiii{14}{\member{ru_nvcsw}}{voluntary context switches}
 177   \lineiii{15}{\member{ru_nivcsw}}{involuntary context switches}
 178 \end{tableiii}
 179
 180   This function will raise a \exception{ValueError} if an invalid
 181   \var{who} parameter is specified. It may also raise
 182   \exception{error} exception in unusual circumstances.
 183
 184   \versionchanged[Added access to values as attributes of the
 185   returned object]{2.3}
 186 \end{funcdesc}
 187
 188 \begin{funcdesc}{getpagesize}{}
 189   Returns the number of bytes in a system page. (This need not be the
 190   same as the hardware page size.) This function is useful for
 191   determining the number of bytes of memory a process is using. The
 192   third element of the tuple returned by \function{getrusage()} describes
 193   memory usage in pages; multiplying by page size produces number of
 194   bytes.
 195 \end{funcdesc}
 196
 197 The following \constant{RUSAGE_*} symbols are passed to the
 198 \function{getrusage()} function to specify which processes information
 199 should be provided for.
 200
 201 \begin{datadesc}{RUSAGE_SELF}
 202   \constant{RUSAGE_SELF} should be used to
 203   request information pertaining only to the process itself.
 204 \end{datadesc}
 205
 206 \begin{datadesc}{RUSAGE_CHILDREN}
 207   Pass to \function{getrusage()} to request resource information for
 208   child processes of the calling process.
 209 \end{datadesc}
 210
 211 \begin{datadesc}{RUSAGE_BOTH}
 212   Pass to \function{getrusage()} to request resources consumed by both
 213   the current process and child processes.  May not be available on all
 214   systems.
 215 \end{datadesc}