GC_MALLOC(1L) GC_MALLOC(1L)
20 April 1994
NAME
GC_malloc, GC_malloc_atomic, GC_free, GC_realloc,
GC_enable_incremental, GC_register_finalizer - Garbage collecting
malloc replacement
SYNOPSIS
#include "gc.h"
# define malloc(n) GC_malloc(n)
cc ... gc.a
DESCRIPTION
GC_malloc and GC_free are plug-in replacements for standard malloc and
free. However, GC_malloc will attempt to reclaim inaccessible space
automaticaly by invoking a conservative garbage collector at
appropriate points. The collector traverses all data structures
accessible by following pointers from the machines registers,
stack(s), data, and bss segments. Inaccessible structures will be
reclaimed. A machine word is considered to be a valid pointer if it
is an address inside an object allocated by GC_malloc or friends.
Unlike the standard implementations of malloc, GC_malloc clears the
newly allocated storage. GC_malloc_atomic does not. Furthermore, it
informs the collector that the resulting object will never contain any
pointers, and should therefore not be scanned by the collector.
GC_free can be used to deallocate objects, but its use is optional,
and discouraged. GC_realloc has the standard realloc semantics. It
preserves pointer-free-ness. GC_register_finalizer allows for
registration of functions that are invoked when an object becomes
inaccessible. It is also possible to use the collector to find
storage leaks in programs destined to be run with standard
malloc/free. The collector can be compiled for thread-safe operation.
Unlike standard malloc, it is safe to call malloc after a previous
malloc call was interrupted by a signal, provided the original malloc
call is not resumed. Debugging versions of many of the above routines
are provided as macros. Their names are identical to the above, but
consist of all capital letters. If GC_DEBUG is defined before gc.h is
included, these routines do additional checking, and allow the leak
detecting version of the collector to produce slightly more useful
output. Without GC_DEBUG defined, they behave exactly like the
lower-case versions. On some machines, collection will be performed
incrementally after a call to GC_enable_incremental. This may
temporarily write protect pages in the heap. See the README file for
more information on how this interacts with system calls that write to
the heap. Other facilities not discussed here include a C++
interface, limited facilities to support incremental collection on
machines without appropriate VM support, provisions for providing more
explicit object layout information to the garbage collector, more
direct support for ``weak'' pointers, etc.
SEE ALSO
The README and gc.h files in the distribution. More detailed
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GC_MALLOC(1L) GC_MALLOC(1L)
20 April 1994
definitions of the functions exported by the collector are given
there. (The above list is not complete.) Boehm, H., and M. Weiser,
"Garbage Collection in an Uncooperative Environment", Software
Practice & Experience, September 1988, pp. 807-820. The malloc(3) man
page.
AUTHOR
Hans-J. Boehm (boehm@parc.xerox.com). Some of the code was written by
others, most notably Alan Demers.
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