.\" .\" Memory.man .\" .\" Extended Tcl memory leak locator. .\"---------------------------------------------------------------------------- .\" Copyright 1992-1999 Karl Lehenbauer and Mark Diekhans. .\" .\" Permission to use, copy, modify, and distribute this software and its .\" documentation for any purpose and without fee is hereby granted, provided .\" that the above copyright notice appear in all copies. Karl Lehenbauer and .\" Mark Diekhans make no representations about the suitability of this .\" software for any purpose. It is provided "as is" without express or .\" implied warranty. .\"---------------------------------------------------------------------------- .\" $Id: Memory.n,v 8.2 1999/03/31 06:37:42 markd Exp $ .\"---------------------------------------------------------------------------- .\" .TH "Memory" TCL "" "Tcl" .BS .SH NAME ckalloc, memory, ckfree, Tcl_DisplayMemory, Tcl_InitMemory, Tcl_ValidateAllMemory - Validated memory allocation interface. .SH SYNOPSIS .nf .B memory \fBinfo\fR .B memory \fBtrace\fR [\fBon|off\fR] .B memory \fBvalidate\fR [\fBon|off\fR] .B memory \fBtrace_on_at_malloc\fR \fInnn\fR .B memory \fBbreak_on_malloc\fR \fInnn\fR .B memory \fBdisplay\fR \fIfile\fR .sp 2 .ft CW #include .sp char * ckalloc (unsigned size) .sp void ckfree (char *ptr) .sp int Tcl_DumpActiveMemory (char *fileName); .sp void Tcl_ValidateAllMemory (char *file, int line) void Tcl_InitMemory (interp) .ft R ' .SH ARGUMENTS .AS Tcl_Interp *fileName .AP uint size in .AP char *ptr in .AP Tcl_Interp *interp in A pointer to the Tcl interpreter. .AP char *file in The filename of the caller of Tcl_ValidateAllMemory. .AP int line in The line number of the caller of Tcl_ValidateAllMemory. .AP char *fileName in File to display list of active memory. .BE .SH DESCRIPTION .SS ckalloc .PP Thi macro allocates memory, in the same manner as \fBmalloc\fR, with the following differences: One, \fBckalloc\fR checks the value returned from \fBmalloc\fR (it calls \fBmalloc\fR for you) and panics if the allocation request fails. Two, if enabled at compile time, a version of \fBckalloc\fR with special memory debugging capabilities replaces the normal version of \fBckalloc\fR, which aids in detecting memory overwrites and leaks (repeated allocations not matched by corresponding frees). .PP Parameters: .RS 2 \fBo \fIsize\fR - The size of the memory block to be allocated. .RE .PP Returns: .RS 2 A pointer to the allocated memory block. .RE ' .SS ckfree .PP This macro frees memory allocated by \fBckalloc\fR. Like \fBckalloc\fR, when memory debugging is enabled, \fBckfree\fR has enhanced capabilities for detecting memory overwrites and leaks. .PP It is very important that you use \fBckalloc\fR when you need to allocate memory, and that you use \fBckfree\fR to free it. Should you use \fBmalloc\fR to allocate and \fBckfree\fR to free, spurious memory validation errors will occur when memory debugging is enabled. Should you use \fBfree\fR to free memory allocated by \fBckalloc\fR, memory corruption will occur when memory debugging is enabled. Any memory that is to be become the property of the Tcl interpreter, such as result space, must be allocated with \fBckalloc\fR. If it is absolutely necessary for an application to pass back \fBmalloc\fRed memory to Tcl, it will work only if Tcl is complied with the \fBTCL_MEM_DEBUG\fR flag turned off. If you convert your application to use this facility, it will help you find memory over runs and lost memory. Note that memory allocated by a C library routine requiring freeing should still be freed with \fBfree\fR, since it calls \fBmalloc\fR rather than \fBckalloc\fR to do the allocation. .PP Parmeters: .RS 2 \fBo \fIptr\fR - The address of a block to free, as returned by ckalloc. .RE .sp ' .SS Tcl_DumpActiveMemory .PP This function will output a list of all currently allocated memory to the specified file. The following information is outputted for each allocated block of memory: starting and ending addresses (excluding guard zone), size, source file where \fBckalloc\fR was called to allocate the block and line number in that file. It is especially useful to call \fBTcl_DumpActiveMemory\fR after the Tcl interpreter has been deleted. .PP Parameters: .RS 2 \fBo \fIfileName\fR - The name of the file to output the memory list to. .RE ' .SS Tcl_ValidateAllMemory .PP Forces a validation of the guard zones of all currently allocated blocks of memory. Normally validation of a block occurs when its freed, unless full validation is enabled, in which case validation of all blocks occurs when \fBckalloc\fR and \fBckfree\fR are called. This function forces the validation to occur at any point. .PP Parameters: .RS 2 \fBo \fIfile\fR - The file that this routine is being called from, normally \fB__FILE__\fR. .br \fBo \fIline\fR - The line that this routine is being called from, normally \fB__LINE__\fR. .RE ' .SH ENABLING MEMORY DEBUGGING .PP To enable memory debugging, Tcl should be recompiled from scratch with \fBTCL_MEM_DEBUG\fR defined. This will also compile in a non-stub version of \fBTcl_InitMemory\fR to add the \fBmemory\fR command to Tcl. .PP \fBTCL_MEM_DEBUG\fR must be either left defined for all modules or undefined for all modules that are going to be linked together. If they are not, link errors will occur, with either \fBTclDbCkfree\fR and \fBTcl_DbCkalloc\fR or \fBTcl_Ckalloc\fR and \fBTcl_Ckfree\fR being undefined. ' .SH GUARD ZONES .PP When memory debugging is enabled, whenever a call to \fBckalloc\fR is made, slightly more memory than requested is allocated so the memory debugging code can keep track of the allocated memory, and also eight-byte ``guard zones'' are placed in front of and behind the space that will be returned to the caller. (The size of the guard zone is defined by the C #define \fBGUARD_SIZE\fR in \fIbaseline/src/ckalloc.c\fR -- it can be extended if you suspect large overwrite problems, at some cost in performance.) A known pattern is written into the guard zones and, on a call to \fBckfree\fR, the guard zones of the space being freed are checked to see if either zone has been modified in any way. If one has been, the guard bytes and their new contents are identified, and a ``low guard failed'' or ``high guard failed'' message is issued. The ``guard failed'' message includes the address of the memory packet and the file name and line number of the code that called \fBckfree\fR. This allows you to detect the common sorts of one-off problems, where not enough space was allocated to contain the data written, for example. ' .SH THE MEMORY COMMAND '@help: debug/memory '@brief: display and debug memory problems ' .TP .B memory \fIoptions\fR .br The Tcl \fBmemory\fR command gives the Tcl developer control of Tcl's memory debugging capabilities. The memory command has several suboptions, which are described below. It is only available when Tcl has been compiled with memory debugging enabled. ' .TP .B memory \fBinfo\fR .br Produces a report containing the total allocations and frees since Tcl began, the current packets allocated (the current number of calls to \fBckalloc\fR not met by a corresponding call to \fBckfree\fR), the current bytes allocated, and the maximum number of packets and bytes allocated. ' .TP .B memory \fBtrace\fR [\fBon|off\fR] .br Turns memory tracing on or off. When memory tracing is on, every call to \fBckalloc\fR causes a line of trace information to be written to \fIstderr\fR, consisting of the word \fIckalloc\fR, followed by the address returned, the amount of memory allocated, and the C filename and line number of the code performing the allocation, for example... .sp \fBckalloc 40e478 98 tclProc.c 1406\fR .sp Calls to \fBckfree\fR are traced in the same manner, except that the word \fIckalloc\fR is replaced by the word \fIckfree\fR. ' .TP .B memory \fBvalidate\fR [\fBon|off\fR] .br Turns memory validation on or off. When memory validation is enabled, on every call to \fBckalloc\fR or \fBckfree\fR, the guard zones are checked for every piece of memory currently in existence that was allocated by \fBckalloc\fR. This has a large performance impact and should only be used when overwrite problems are strongly suspected. The advantage of enabling memory validation is that a guard zone overwrite can be detected on the first call to \fBckalloc\fR or \fBckfree\fR after the overwrite occurred, rather than when the specific memory with the overwritten guard zone(s) is freed, which may occur long after the overwrite occurred. ' .TP .B memory \fBtrace_on_at_malloc\fR \fInnn\fR .br Enable memory tracing after \fInnn\fR \fBckallocs\fR have been performed. For example, if you enter \fBmemory trace_on_at_malloc 100\fR, after the 100th call to \fBckalloc\fR, memory trace information will begin being displayed for all allocations and frees. Since there can be a lot of memory activity before a problem occurs, judicious use of this option can reduce the slowdown caused by tracing (and the amount of trace information produced), if you can identify a number of allocations that occur before the problem sets in. The current number of memory allocations that have occurred since Tcl started is printed on a guard zone failure. .TP .B memory \fBbreak_on_malloc\fR \fInnn\fR .br After the \fBnnn\fR allocations have been performed, \fBckallocs\fR output a message to this effect and that it is now attempting to enter the C debugger. Tcl will then issue a \fISIGINT\fR signal against itself. If you are running Tcl under a C debugger, it should then enter the debugger command mode. ' .TP .B memory \fBdisplay\fR \fIfile\fR .br Write a list of all currently allocated memory to the specified file. '@endhelp ' .SH DEBUGGING DIFFICULT MEMORY CORRUPTION PROBLEMS .PP Normally, Tcl compiled with memory debugging enabled will make it easy to isolate a corruption problem. Turning on memory validation with the memory command can help isolate difficult problems. If you suspect (or know) that corruption is occurring before the Tcl interpreter comes up far enough for you to issue commands, you can set \fBMEM_VALIDATE\fR define, recompile tclCkalloc.c and rebuild Tcl. This will enable memory validation from the first call to \fBckalloc\fR, again, at a large performance impact. .PP If you are desperate and validating memory on every call to \fBckalloc\fR and \fBckfree\fR isn't enough, you can explicitly call \fBTcl_ValidateAllMemory\fR directly at any point. It takes a \fIchar *\fR and an \fIint\fR which are normally the filename and line number of the caller, but they can actually be anything you want. Remember to remove the calls after you find the problem. ' .SH KEYWORDS ckalloc, ckfree, free, memory, malloc