2002-02-17 21:56:45 +00:00
|
|
|
<html>
|
|
|
|
|
<head>
|
|
|
|
|
<title>libsm : Memory Allocation</title>
|
|
|
|
|
</head>
|
|
|
|
|
<body>
|
|
|
|
|
|
|
|
|
|
<a href="index.html">Back to libsm overview</a>
|
|
|
|
|
|
|
|
|
|
<center>
|
|
|
|
|
<h1> libsm : Memory Allocation </h1>
|
2002-06-11 21:12:04 +00:00
|
|
|
<br> $Id: heap.html,v 1.9 2000/12/08 21:41:42 ca Exp $
|
2002-02-17 21:56:45 +00:00
|
|
|
</center>
|
|
|
|
|
|
|
|
|
|
<h2> Introduction </h2>
|
|
|
|
|
|
|
|
|
|
The heap package provides a layer of abstraction on top of
|
|
|
|
|
<tt>malloc</tt>, <tt>realloc</tt> and <tt>free</tt>
|
|
|
|
|
that provides optional error checking and memory leak detection,
|
|
|
|
|
and which optionally raises an exception when an allocation request
|
|
|
|
|
cannot be satisfied.
|
|
|
|
|
|
|
|
|
|
<h2> Synopsis </h2>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
#include <sm/heap.h>
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
** Wrappers for malloc, realloc, free
|
|
|
|
|
*/
|
|
|
|
|
void *sm_malloc(size_t size);
|
|
|
|
|
void *sm_realloc(void *ptr, size_t size);
|
|
|
|
|
void sm_free(void *ptr);
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
** Wrappers for malloc, realloc that raise an exception instead of
|
|
|
|
|
** returning NULL on heap exhaustion.
|
|
|
|
|
*/
|
|
|
|
|
void *sm_malloc_x(size_t size);
|
|
|
|
|
void *sm_realloc_x(void *ptr, size_t size);
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
** Print a list of currently allocated blocks,
|
|
|
|
|
** used to diagnose memory leaks.
|
|
|
|
|
*/
|
|
|
|
|
void sm_heap_report(FILE *stream, int verbosity);
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
** Low level interfaces.
|
|
|
|
|
*/
|
|
|
|
|
int sm_heap_group();
|
|
|
|
|
int sm_heap_setgroup(int g);
|
|
|
|
|
int sm_heap_newgroup();
|
|
|
|
|
void *sm_malloc_tagged(size_t size, char *file, int line, int group);
|
|
|
|
|
void *sm_malloc_tagged_x(size_t size, char *file, int line, int group);
|
|
|
|
|
bool sm_heap_register(void *ptr, size_t size, char *file, int line);
|
|
|
|
|
</pre>
|
|
|
|
|
|
|
|
|
|
<h2> How to allocate and free memory </h2>
|
|
|
|
|
|
|
|
|
|
<tt>sm_malloc</tt>, <tt>sm_realloc</tt> and <tt>sm_free</tt>
|
|
|
|
|
are portable plug in replacements
|
|
|
|
|
for <tt>malloc</tt>, <tt>realloc</tt> and <tt>free</tt> that provide
|
|
|
|
|
error checking and memory leak detection.
|
|
|
|
|
<tt>sm_malloc_x</tt> and <tt>sm_realloc_x</tt>
|
|
|
|
|
are variants of
|
|
|
|
|
<tt>sm_malloc</tt> and <tt>sm_realloc</tt>
|
|
|
|
|
that raise an exception on error.
|
|
|
|
|
To use the package effectively,
|
|
|
|
|
all calls to <tt>malloc</tt>, <tt>realloc</tt> and <tt>free</tt>
|
|
|
|
|
should be replaced by calls
|
|
|
|
|
to the corresponding <tt>sm_</tt>* routines.
|
|
|
|
|
|
|
|
|
|
<dl>
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> void *sm_malloc(size_t size) </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
This function is a plug-in replacement for <tt>malloc</tt>.
|
|
|
|
|
It allocates <tt>size</tt> bytes of memory on the heap
|
|
|
|
|
and returns a pointer to it,
|
|
|
|
|
or it returns <tt>NULL</tt> on failure.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
The C standard says that <tt>malloc(0)</tt> may return
|
|
|
|
|
either <tt>NULL</tt> or a non-<tt>NULL</tt> value.
|
|
|
|
|
To ensure consistent behaviour on all platforms,
|
|
|
|
|
<tt>sm_malloc(0)</tt> is equivalent to <tt>sm_malloc(1)</tt>.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
In addition, if heap checking is enabled, then <tt>sm_malloc</tt>
|
|
|
|
|
maintains a hash table describing all currently allocated
|
|
|
|
|
memory blocks. This table is used for argument validity
|
|
|
|
|
checking in <tt>sm_realloc</tt> and <tt>sm_free</tt>,
|
|
|
|
|
and it can be printed using <tt>sm_heap_report</tt>
|
|
|
|
|
as an aid to finding memory leaks.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> void *sm_malloc_x(size_t size) </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
This function is just like <tt>sm_malloc</tt>
|
|
|
|
|
except that it raises the <tt>SmHeapOutOfMemory</tt> exception
|
|
|
|
|
instead of returning <tt>NULL</tt> on error.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> void *sm_realloc(void *ptr, size_t size) </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
This function is a plug-in replacement for <tt>realloc</tt>.
|
|
|
|
|
If <tt>ptr</tt> is null then this call is equivalent
|
|
|
|
|
to <tt>sm_malloc(size)</tt>.
|
|
|
|
|
Otherwise, the size of the object pointed to by <tt>ptr</tt>
|
|
|
|
|
is changed to <tt>size</tt> bytes, and a pointer to the
|
|
|
|
|
(possibly moved) object is returned.
|
|
|
|
|
If the space cannot be allocated, then the object pointed to
|
|
|
|
|
by <tt>ptr</tt> is unchanged and <tt>NULL</tt> is returned.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
If <tt>size</tt> is 0 then we pretend that <tt>size</tt> is 1.
|
|
|
|
|
This may be a mistake.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
If ptr is not NULL and heap checking is enabled,
|
|
|
|
|
then ptr is required to be a value that was
|
|
|
|
|
previously returned by sm_malloc or sm_realloc, and which
|
|
|
|
|
has not yet been freed by sm_free. If this condition is not
|
|
|
|
|
met, then the program is aborted using sm_abort.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> void *sm_realloc_x(void *ptr, size_t size) </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
This function is just like <tt>sm_realloc</tt>
|
|
|
|
|
except that it raises the SmHeapOutOfMemory exception
|
|
|
|
|
instead of returning <tt>NULL</tt> on error.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> void sm_free(void *ptr) </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
This function is a plug-in replacement for free.
|
|
|
|
|
If heap checking is disabled, then this function is equivalent
|
|
|
|
|
to a call to free. Otherwise, the following additional semantics
|
|
|
|
|
apply.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
If ptr is NULL, this function has no effect.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
Otherwise, ptr is required to be a value that was
|
|
|
|
|
previously returned by sm_malloc or sm_realloc, and which
|
|
|
|
|
has not yet been freed by sm_free. If this condition is not
|
|
|
|
|
met, then the program is aborted using sm_abort.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
Otherwise, if there is no error, then the block pointed to by ptr
|
|
|
|
|
will be set to all zeros before free() is called. This is intended
|
|
|
|
|
to assist in detecting the use of dangling pointers.
|
|
|
|
|
</dl>
|
|
|
|
|
|
|
|
|
|
<h2> How to control tag information </h2>
|
|
|
|
|
|
|
|
|
|
When heap checking is enabled,
|
|
|
|
|
the heap package maintains a hash table which associates the
|
|
|
|
|
following values with each currently allocated block:
|
|
|
|
|
|
|
|
|
|
<dl>
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> size_t size </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
The size of the block.
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> char *tag </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
By default, this is the name of the source file from which
|
|
|
|
|
the block was allocated, but you can specify an arbitrary
|
|
|
|
|
string pointer, or <tt>NULL</tt>.
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> int num </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
By default, this is the line number from which the block was
|
|
|
|
|
allocated.
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> int group </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
By convention, group==0 indicates that the block is permanently
|
|
|
|
|
allocated and will never be freed. The meanings of other group
|
|
|
|
|
numbers are defined by the application developer.
|
|
|
|
|
Unless you take special action, all blocks allocated by
|
|
|
|
|
<tt>sm_malloc</tt> and <tt>sm_malloc_x</tt> will be assigned
|
|
|
|
|
to group 1.
|
|
|
|
|
</dl>
|
|
|
|
|
|
|
|
|
|
These tag values are printed by <tt>sm_heap_report</tt>,
|
|
|
|
|
and are used to help analyze memory allocation behaviour
|
|
|
|
|
and to find memory leaks.
|
|
|
|
|
The following functions give you precise control over the
|
|
|
|
|
tag values associated with each allocated block.
|
|
|
|
|
|
|
|
|
|
<dl>
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> void *sm_malloc_tagged(size_t size, int tag, int num, int group) </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
Just like <tt>sm_malloc</tt>, except you directly specify
|
|
|
|
|
all of the tag values.
|
|
|
|
|
If heap checking is disabled at compile time, then a call
|
|
|
|
|
to <tt>sm_malloc_tagged</tt> is macro expanded to
|
|
|
|
|
a call to <tt>malloc</tt>.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
Note that the expression <tt>sm_malloc(size)</tt> is macro expanded to
|
|
|
|
|
|
|
|
|
|
<blockquote><pre>
|
|
|
|
|
sm_malloc_tagged(size, __FILE__, __LINE__, sm_heap_group())
|
|
|
|
|
</pre></blockquote>
|
|
|
|
|
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> void *sm_malloc_tagged_x(size_t size, int tag, int num, int group) </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
A variant of <tt>sm_malloc_tagged</tt>
|
|
|
|
|
that raises an exception on error.
|
|
|
|
|
A call to <tt>sm_malloc_x</tt> is macro expanded
|
|
|
|
|
to a call to <tt>sm_malloc_tagged_x</tt>.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> int sm_heap_group() </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
The heap package maintains a thread-local variable containing
|
|
|
|
|
the current group number.
|
|
|
|
|
This is the group that <tt>sm_malloc</tt> and <tt>sm_malloc_x</tt>
|
|
|
|
|
will assign a newly allocated block to.
|
|
|
|
|
The initial value of this variable is 1.
|
|
|
|
|
The current value of this variable is returned by
|
|
|
|
|
<tt>sm_heap_group()</tt>.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> int sm_heap_setgroup(int g) </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
Set the current group to the specified value.
|
|
|
|
|
</dl>
|
|
|
|
|
|
|
|
|
|
Here are two examples of how you might use these interfaces.
|
|
|
|
|
|
|
|
|
|
<ol>
|
|
|
|
|
<li>
|
|
|
|
|
One way to detect memory leaks is to turn on heap checking
|
|
|
|
|
and call <tt>sm_heap_report(stdout,2)</tt>
|
|
|
|
|
when the program exits.
|
|
|
|
|
This prints a list of all allocated blocks that do not belong to group 0.
|
|
|
|
|
(Blocks in group 0 are assumed to be permanently allocated,
|
|
|
|
|
and so their existence at program exit does not indicate a leak.)
|
|
|
|
|
If you want to allocate a block and assign it to group 0,
|
|
|
|
|
you have two choices:
|
|
|
|
|
|
|
|
|
|
<blockquote><pre>
|
|
|
|
|
int g = sm_heap_group();
|
|
|
|
|
sm_heap_setgroup(0);
|
|
|
|
|
p = sm_malloc_x(size);
|
|
|
|
|
sm_heap_setgroup(g);
|
|
|
|
|
</pre></blockquote>
|
|
|
|
|
|
|
|
|
|
or
|
|
|
|
|
|
|
|
|
|
<blockquote><pre>
|
|
|
|
|
p = sm_malloc_tagged_x(size, __FILE__, __LINE__, 0);
|
|
|
|
|
</pre></blockquote>
|
|
|
|
|
|
|
|
|
|
<li>
|
|
|
|
|
Suppose you have a utility function foo_alloc which allocates
|
|
|
|
|
and initializes a 'foo' object. When sm_heap_report is called,
|
|
|
|
|
all unfreed 'foo' objects will be reported to have the same
|
|
|
|
|
source code file name and line number.
|
|
|
|
|
That might make it difficult to determine where a memory leak is.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
Here is how you can arrange for more precise reporting for
|
|
|
|
|
unfreed foo objects:
|
|
|
|
|
|
|
|
|
|
<blockquote><pre>
|
|
|
|
|
#include <sm/heap.h>
|
|
|
|
|
|
|
|
|
|
#if SM_HEAP_CHECK
|
|
|
|
|
# define foo_alloc_x() foo_alloc_tagged_x(__FILE__,__LINE)
|
|
|
|
|
FOO *foo_alloc_tagged_x(char *, int);
|
|
|
|
|
#else
|
|
|
|
|
FOO *foo_alloc_x(void);
|
|
|
|
|
# define foo_alloc_tagged_x(file,line) foo_alloc_x()
|
|
|
|
|
#endif
|
|
|
|
|
|
|
|
|
|
...
|
|
|
|
|
|
|
|
|
|
#if SM_HEAP_CHECK
|
|
|
|
|
FOO *
|
|
|
|
|
foo_alloc_tagged_x(char *file, int line)
|
|
|
|
|
#else
|
|
|
|
|
FOO *
|
|
|
|
|
foo_alloc_x(void)
|
|
|
|
|
#endif
|
|
|
|
|
{
|
|
|
|
|
FOO *p;
|
|
|
|
|
|
|
|
|
|
p = sm_malloc_tagged_x(sizeof(FOO), file, line, sm_heap_group());
|
|
|
|
|
...
|
|
|
|
|
return p;
|
|
|
|
|
}
|
|
|
|
|
</pre></blockquote>
|
|
|
|
|
</ol>
|
|
|
|
|
|
|
|
|
|
<h2> How to dump the block list </h2>
|
|
|
|
|
|
|
|
|
|
To perform memory leak detection, you need to arrange for your
|
|
|
|
|
program to call sm_heap_report at appropriate times.
|
|
|
|
|
|
|
|
|
|
<dl>
|
|
|
|
|
<dt>
|
|
|
|
|
<tt> void sm_heap_report(FILE *stream, int verbosity) </tt>
|
|
|
|
|
<dd>
|
|
|
|
|
If heap checking is disabled, this function does nothing.
|
|
|
|
|
If verbosity <= 0, this function does nothing.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
If verbosity >= 1, then sm_heap_report prints a single line
|
|
|
|
|
to stream giving the total number of bytes currently allocated.
|
|
|
|
|
If you call sm_heap_report each time the program has reached a
|
|
|
|
|
"ground state", and the reported amount of heap storage is
|
|
|
|
|
monotonically increasing, that indicates a leak.
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
If verbosity >= 2, then sm_heap_report additionally prints one line
|
|
|
|
|
for each block of memory currently allocated, providing that
|
|
|
|
|
the group != 0.
|
|
|
|
|
(Such blocks are assumed to be permanently allocated storage, and
|
|
|
|
|
are not reported to cut down the level of noise.)
|
|
|
|
|
<p>
|
|
|
|
|
|
|
|
|
|
If verbosity >= 3, then sm_heap_report prints one line for each
|
|
|
|
|
allocated block, regardless of the group.
|
|
|
|
|
</dl>
|
|
|
|
|
|
|
|
|
|
<h2> How to enable heap checking </h2>
|
|
|
|
|
|
|
|
|
|
The overhead of using the package can be made as small as you want.
|
|
|
|
|
You have three options:
|
|
|
|
|
|
|
|
|
|
<ol>
|
|
|
|
|
<li>
|
|
|
|
|
If you compile your software with -DSM_HEAP_CHECK=0 then
|
|
|
|
|
sm_malloc, sm_realloc and sm_free will be redefined
|
|
|
|
|
as macros that call malloc, realloc, and free. In this case,
|
|
|
|
|
there is zero overhead.
|
|
|
|
|
<li>
|
|
|
|
|
If you do not define -DSM_HEAP_CHECK=0, and you do not explicitly
|
|
|
|
|
turn on heap checking at run time, then your program will run
|
|
|
|
|
without error checking and memory leak detection, and the additional
|
|
|
|
|
cost of calling sm_malloc, sm_realloc and sm_free is a
|
|
|
|
|
function call and test. That overhead is sufficiently low that
|
|
|
|
|
the checking code can be left compiled in a production environment.
|
|
|
|
|
<li>
|
|
|
|
|
If you do not define -DSM_HEAP_CHECK=0, and you explicitly turn on
|
|
|
|
|
heap checking at run time, then the additional cost of calling
|
|
|
|
|
sm_malloc, sm_realloc and sm_free is a hash table lookup.
|
|
|
|
|
</ol>
|
|
|
|
|
|
|
|
|
|
Here's how to modify your application to use the heap package.
|
|
|
|
|
First, change all calls to malloc, realloc and free to sm_malloc,
|
|
|
|
|
sm_realloc and sm_free.
|
|
|
|
|
Make sure that there is a -d command line option that
|
|
|
|
|
uses the libsm debug package to enable named debug options.
|
|
|
|
|
Add the following code to your program just before it calls exit,
|
|
|
|
|
or register an atexit handler function containing the following code:
|
|
|
|
|
|
|
|
|
|
<blockquote><pre>
|
|
|
|
|
#if SM_HEAP_CHECK
|
|
|
|
|
/* dump the heap, if we are checking for memory leaks */
|
|
|
|
|
if (sm_debug_active(&SmHeapCheck, 2))
|
|
|
|
|
sm_heap_report(stdout, sm_debug_level(&SmHeapCheck) - 1);
|
|
|
|
|
#endif
|
|
|
|
|
</pre></blockquote>
|
|
|
|
|
|
|
|
|
|
To turn on heap checking, use the command line option "-dsm_check_heap.1".
|
|
|
|
|
This will cause a table of all currently allocated blocks to be
|
|
|
|
|
maintained. The table is used by sm_realloc and sm_free to perform
|
|
|
|
|
validity checking on the first argument.
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
The command line option "-dsm_check_heap.2" will cause your application
|
|
|
|
|
to invoke sm_heap_report with verbosity=1 just before exit.
|
|
|
|
|
That will print a single line reporting total storage allocation.
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
The command line option "-dsm_check_heap.3" will cause your application
|
|
|
|
|
to invoke sm_heap_report with verbosity=2 just before exit.
|
|
|
|
|
This will print a list of all leaked blocks.
|
|
|
|
|
|
|
|
|
|
<p>
|
|
|
|
|
The command line option "-dsm_check_heap.4" will cause your application
|
|
|
|
|
to invoke sm_heap_report with verbosity=3 just before exit.
|
|
|
|
|
This will print a list of all allocated blocks.
|
|
|
|
|
|
|
|
|
|
<h2> Using sm_heap_register </h2>
|
|
|
|
|
|
|
|
|
|
Suppose you call a library routine foo that allocates a block of storage
|
|
|
|
|
for you using malloc, and expects you to free the block later using
|
|
|
|
|
free. Because the storage was not allocated using sm_malloc, you
|
|
|
|
|
will normally get an abort if you try to pass the pointer to
|
|
|
|
|
sm_free. The way to fix this problem is to 'register' the pointer
|
|
|
|
|
returned by foo with the heap package, by calling sm_heap_register:
|
|
|
|
|
|
|
|
|
|
<blockquote><pre>
|
|
|
|
|
bool sm_heap_register(ptr, size, file, line, group)
|
|
|
|
|
</pre></blockquote>
|
|
|
|
|
|
|
|
|
|
The 'ptr' argument is the pointer returned by foo. The 'size' argument
|
|
|
|
|
can be smaller than the actual size of the allocated block, but it must
|
|
|
|
|
not be larger. The file and line arguments indicate at which line of
|
|
|
|
|
source code the block was allocated, and is printed by sm_heap_report.
|
|
|
|
|
For group, you probably want to pass sm_heap_group().
|
|
|
|
|
<p>
|
|
|
|
|
This function returns <tt>true</tt> on success,
|
|
|
|
|
or <tt>false</tt> if it failed due to heap exhaustion.
|
|
|
|
|
|
|
|
|
|
</body>
|
|
|
|
|
</html>
|
