raw/mann/ckalloc.n

   1 .\"
   2 .\" Memory.man
   3 .\"
   4 .\" Extended Tcl memory leak locator.
   5 .\"----------------------------------------------------------------------------
   6 .\" Copyright 1992-1999 Karl Lehenbauer and Mark Diekhans.
   7 .\"
   8 .\" Permission to use, copy, modify, and distribute this software and its
   9 .\" documentation for any purpose and without fee is hereby granted, provided
  10 .\" that the above copyright notice appear in all copies.  Karl Lehenbauer and
  11 .\" Mark Diekhans make no representations about the suitability of this
  12 .\" software for any purpose.  It is provided "as is" without express or
  13 .\" implied warranty.
  14 .\"----------------------------------------------------------------------------
  15 .\" $Id: ckalloc.n,v 1.1 2003/12/20 03:31:54 bbbush Exp $
  16 .\"----------------------------------------------------------------------------
  17 .\"
  18 .TH "Memory" TCL "" "Tcl"
  19 .BS
  20 .SH NAME
  21 ckalloc, memory, ckfree, Tcl_DisplayMemory, Tcl_InitMemory, Tcl_ValidateAllMemory - Validated memory allocation interface.
  22 .SH SYNOPSIS
  23 .nf
  24 .B memory \fBinfo\fR
  25
  26 .B memory \fBtrace\fR [\fBon|off\fR]
  27
  28 .B memory \fBvalidate\fR [\fBon|off\fR]
  29
  30 .B memory \fBtrace_on_at_malloc\fR \fInnn\fR
  31
  32 .B memory \fBbreak_on_malloc\fR \fInnn\fR
  33
  34 .B memory \fBdisplay\fR \fIfile\fR
  35
  36 .sp 2
  37 .ft CW
  38 #include <tcl.h>
  39 .sp
  40 char *
  41 ckalloc (unsigned size)
  42 .sp
  43 void
  44 ckfree (char *ptr)
  45 .sp
  46 int
  47 Tcl_DumpActiveMemory (char *fileName);
  48 .sp
  49 void
  50 Tcl_ValidateAllMemory (char *file,
  51                        int   line)
  52
  53 void
  54 Tcl_InitMemory (interp)
  55 .ft R
  56 '
  57 .SH ARGUMENTS
  58 .AS Tcl_Interp *fileName
  59 .AP uint size in
  60
  61 .AP char *ptr in
  62 .AP Tcl_Interp *interp in
  63 A pointer to the Tcl interpreter.
  64 .AP char *file in
  65 The filename of the caller of Tcl_ValidateAllMemory.
  66 .AP int line in
  67 The line number of the caller of Tcl_ValidateAllMemory.
  68 .AP char *fileName in
  69 File to display list of active memory.
  70 .BE
  71
  72 .SH DESCRIPTION
  73 .SS ckalloc
  74 .PP
  75 Thi macro allocates memory, in the same manner as \fBmalloc\fR, with the
  76 following differences: One, \fBckalloc\fR checks the value returned from
  77 \fBmalloc\fR (it calls \fBmalloc\fR for you) and panics if the allocation
  78 request fails.  Two, if enabled at compile time, a version of \fBckalloc\fR
  79 with special memory debugging capabilities replaces the normal version of
  80 \fBckalloc\fR, which aids in detecting memory overwrites and leaks (repeated
  81 allocations not matched by corresponding frees).
  82 .PP
  83 Parameters:
  84 .RS 2
  85 \fBo \fIsize\fR - The size of the memory block to be allocated.
  86 .RE
  87 .PP
  88 Returns:
  89 .RS 2
  90 A pointer to the allocated memory block.
  91 .RE
  92 '
  93 .SS ckfree
  94 .PP
  95 This macro frees memory allocated by \fBckalloc\fR.  Like \fBckalloc\fR,
  96 when memory debugging is enabled, \fBckfree\fR has enhanced capabilities
  97 for detecting memory overwrites and leaks.
  98 .PP
  99 It is very important that you use \fBckalloc\fR when you need to allocate
 100 memory, and that you use \fBckfree\fR to free it.  Should you use \fBmalloc\fR
 101 to allocate and \fBckfree\fR to free, spurious memory validation errors will
 102 occur when memory debugging is enabled.  Should you use \fBfree\fR to free
 103 memory allocated by \fBckalloc\fR, memory corruption will occur when memory
 104 debugging is enabled.  Any memory that is to be become the property of the Tcl
 105 interpreter, such as result space, must be allocated with \fBckalloc\fR.  If
 106 it is absolutely necessary for an application to pass back \fBmalloc\fRed
 107 memory to Tcl, it will work only if Tcl is complied with the
 108 \fBTCL_MEM_DEBUG\fR flag turned off.  If you convert your application to use
 109 this facility, it will help you find memory over runs and lost memory.  Note
 110 that memory allocated by a C library routine requiring freeing should still be
 111 freed with \fBfree\fR, since it calls \fBmalloc\fR rather than \fBckalloc\fR
 112 to do the allocation.
 113 .PP
 114 Parmeters:
 115 .RS 2
 116 \fBo \fIptr\fR - The address of a block to free, as returned by ckalloc.
 117 .RE
 118 .sp
 119 '
 120 .SS Tcl_DumpActiveMemory
 121 .PP
 122 This function will output a list of all currently allocated memory to the
 123 specified file.  The following information is outputted for each allocated
 124 block of memory: starting and ending addresses (excluding guard zone), size,
 125 source file where \fBckalloc\fR was called to allocate the block and line
 126 number in that file.  It is especially useful to call
 127 \fBTcl_DumpActiveMemory\fR after the Tcl interpreter has been deleted.
 128 .PP
 129 Parameters:
 130 .RS 2
 131 \fBo \fIfileName\fR - The name of the file to output the memory list to.
 132 .RE
 133 '
 134 .SS Tcl_ValidateAllMemory
 135 .PP
 136 Forces a validation of the guard zones of all currently allocated blocks
 137 of memory.  Normally validation of a block occurs when its freed, unless
 138 full validation is enabled, in which case validation of all blocks
 139 occurs when \fBckalloc\fR and \fBckfree\fR are called.  This function forces
 140 the validation to occur at any point.
 141 .PP
 142 Parameters:
 143 .RS 2
 144 \fBo \fIfile\fR - The file that this routine is being called from, normally
 145 \fB__FILE__\fR.
 146 .br
 147 \fBo \fIline\fR - The line that this routine is being called from, normally
 148 \fB__LINE__\fR.
 149 .RE
 150 '
 151 .SH ENABLING MEMORY DEBUGGING
 152 .PP
 153 To enable memory debugging, Tcl should be recompiled from scratch with
 154 \fBTCL_MEM_DEBUG\fR defined.  This will also compile in
 155 a non-stub version of \fBTcl_InitMemory\fR
 156 to add the \fBmemory\fR command to Tcl.
 157 .PP
 158 \fBTCL_MEM_DEBUG\fR must be either left defined for all modules or undefined
 159 for all modules that are going to be linked together.  If they are not, link
 160 errors will occur, with either \fBTclDbCkfree\fR and \fBTcl_DbCkalloc\fR or
 161 \fBTcl_Ckalloc\fR and \fBTcl_Ckfree\fR being undefined.
 162 '
 163 .SH GUARD ZONES
 164 .PP
 165 When memory debugging is enabled, whenever a call to \fBckalloc\fR is
 166 made, slightly more memory than requested is allocated so the memory debugging
 167 code can keep track
 168 of the allocated memory, and also
 169 eight-byte ``guard zones'' are placed in front of and behind the space that
 170 will be returned to the caller.  (The size of the guard zone is defined
 171 by the C #define \fBGUARD_SIZE\fR in \fIbaseline/src/ckalloc.c\fR -- it
 172 can be extended if you suspect large overwrite problems, at some cost in
 173 performance.)  A known pattern is written into the guard zones and,
 174 on a call to \fBckfree\fR, the guard zones of the space being freed
 175 are checked to see if either zone has been modified in any way.
 176 If one has been, the guard bytes and their new contents are identified,
 177 and a ``low guard failed'' or ``high guard failed'' message is issued.
 178 The ``guard failed'' message includes the address of the memory packet
 179 and the file name and line number of the code that called \fBckfree\fR.
 180 This allows you to detect the common sorts of one-off problems, where
 181 not enough space was allocated to contain the data written, for example.
 182 '
 183 .SH THE MEMORY COMMAND
 184 '@help: debug/memory
 185 '@brief: display and debug memory problems
 186 '
 187 .TP
 188 .B memory \fIoptions\fR
 189 .br
 190 The Tcl \fBmemory\fR command gives the Tcl developer control of Tcl's memory
 191 debugging capabilities.  The memory command has several suboptions, which are
 192 described below.  It is only available when Tcl has been compiled with memory
 193 debugging enabled.
 194 '
 195 .TP
 196 .B memory \fBinfo\fR
 197 .br
 198 Produces a report containing the total allocations and frees since
 199 Tcl began, the current packets allocated (the current
 200 number of calls to \fBckalloc\fR not met by a corresponding call
 201 to \fBckfree\fR), the current bytes allocated, and the maximum number
 202 of packets and bytes allocated.
 203 '
 204 .TP
 205 .B memory \fBtrace\fR [\fBon|off\fR]
 206 .br
 207 Turns memory tracing on or off.
 208 When memory tracing is on, every call to \fBckalloc\fR causes a line of
 209 trace information to be written to \fIstderr\fR, consisting of the
 210 word \fIckalloc\fR, followed by the address returned, the amount of
 211 memory allocated, and the C filename and line number of the code performing
 212 the allocation, for example...
 213 .sp
 214    \fBckalloc 40e478 98 tclProc.c 1406\fR
 215 .sp
 216 Calls to \fBckfree\fR are traced in the same manner, except that the
 217 word \fIckalloc\fR is replaced by the word \fIckfree\fR.
 218 '
 219 .TP
 220 .B memory \fBvalidate\fR [\fBon|off\fR]
 221 .br
 222 Turns memory validation on or off.
 223 When memory validation is enabled, on every call to
 224 \fBckalloc\fR or \fBckfree\fR, the guard zones are checked for every
 225 piece of memory currently in existence that was allocated by \fBckalloc\fR.
 226 This has a large performance impact and should only be used when
 227 overwrite problems are strongly suspected.  The advantage of enabling
 228 memory validation is that a guard zone overwrite can be detected on
 229 the first call to \fBckalloc\fR or \fBckfree\fR after the overwrite
 230 occurred, rather than when the specific memory with the overwritten
 231 guard zone(s) is freed, which may occur long after the overwrite occurred.
 232 '
 233 .TP
 234 .B memory \fBtrace_on_at_malloc\fR \fInnn\fR
 235 .br
 236 Enable memory tracing after \fInnn\fR \fBckallocs\fR have been performed.
 237 For example, if you enter \fBmemory trace_on_at_malloc 100\fR,
 238 after the 100th call to \fBckalloc\fR, memory trace information will begin
 239 being displayed for all allocations and frees.  Since there can be a lot
 240 of memory activity before a problem occurs, judicious use of this option
 241 can reduce the slowdown caused by tracing (and the amount of trace information
 242 produced), if you can identify a number of allocations that occur before
 243 the problem sets in.  The current number of memory allocations that have
 244 occurred since Tcl started is printed on a guard zone failure.
 245 .TP
 246 .B memory \fBbreak_on_malloc\fR \fInnn\fR
 247 .br
 248 After the \fBnnn\fR allocations have been performed, \fBckallocs\fR
 249 output a message to this effect and that it is now attempting to enter
 250 the C debugger.  Tcl will then issue a \fISIGINT\fR signal against itself.
 251 If you are running Tcl under a C debugger, it should then enter the debugger
 252 command mode.
 253 '
 254 .TP
 255 .B memory \fBdisplay\fR \fIfile\fR
 256 .br
 257 Write a list of all currently allocated memory to the specified file.
 258 '@endhelp
 259 '
 260 .SH DEBUGGING DIFFICULT MEMORY CORRUPTION PROBLEMS
 261 .PP
 262 Normally, Tcl compiled with memory debugging enabled will make it easy to isolate
 263 a corruption problem.  Turning on memory validation with the memory command
 264 can help isolate difficult problems.
 265 If you suspect (or know) that corruption is
 266 occurring before the Tcl interpreter comes up far enough for you to
 267 issue commands, you can set \fBMEM_VALIDATE\fR define, recompile
 268 tclCkalloc.c and rebuild Tcl.  This will enable memory validation
 269 from the first call to \fBckalloc\fR, again, at a large performance impact.
 270 .PP
 271 If you are desperate and validating memory on every call to \fBckalloc\fR
 272 and \fBckfree\fR isn't enough, you can explicitly call
 273 \fBTcl_ValidateAllMemory\fR directly at any point.  It takes a \fIchar *\fR
 274 and an \fIint\fR which are normally the filename and line number of the
 275 caller, but they can actually be anything you want.  Remember to remove
 276 the calls after you find the problem.
 277 '
 278 .SH KEYWORDS
 279 ckalloc, ckfree, free, memory, malloc
 280
 281