gc man page on Archlinux

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gc(3)									 gc(3)

       GC_malloc,  GC_malloc_atomic,  GC_free, GC_realloc, GC_enable_incremen‐
       tal,    GC_register_finalizer,	 GC_malloc_ignore_off_page,    GC_mal‐
       loc_atomic_ignore_off_page,  GC_set_warn_proc - Garbage collecting mal‐
       loc replacement

       #include "gc.h"
       void * GC_malloc(size_t size);
       void GC_free(void *ptr);
       void * GC_realloc(void *ptr, size_t size);

       cc ... gc.a

       GC_malloc and GC_free are plug-in replacements for standard malloc  and
       free.   However,	 GC_malloc  will attempt to reclaim inaccessible space
       automatically by invoking a conservative garbage collector at appropri‐
       ate  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.

       In  most	 cases it is preferable to call the macros GC_MALLOC, GC_FREE,
       etc.  instead of calling GC_malloc and friends directly.	  This	allows
       debugging  versions  of	the  routines  to  be  substituted by defining
       GC_DEBUG before including gc.h.

       See the documentation in the include files gc_cpp.h and gc_allocator.h,
       as well as the gcinterface.html file in the distribution, for an alter‐
       nate, C++ specific interface to the garbage collector.  Note  that  C++
       programs generally need to be careful to ensure that all allocated mem‐
       ory (whether via new, malloc, or STL  allocators)  that	may  point  to
       garbage	collected  memory  is  either  itself garbage collected, or at
       least traced by the collector.

       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
       generally discouraged.  GC_realloc has the standard realloc  semantics.
       It  preserves pointer-free-ness.	 GC_register_finalizer allows for reg‐
       istration of functions that are invoked when an object becomes inacces‐

       The  garbage  collector	tries  to avoid allocating memory at locations
       that already appear to be referenced before allocation.	(Such apparent
       ``pointers''  are  usually large integers and the like that just happen
       to look like an address.)  This may make it hard to allocate very large
       objects.	 An attempt to do so may generate a warning.

       GC_malloc_ignore_off_page  and  GC_malloc_atomic_ignore_off_page inform
       the collector that the client code will always maintain	a  pointer  to
       near the beginning of the object (within the first 512 bytes), and that
       pointers beyond that can be ignored by the collector.   This  makes  it
       much easier for the collector to place large objects.  These are recom‐
       mended for large object allocation.  (Objects  expected	to  be	larger
       than about 100KBytes should be allocated this way.)

       It  is also possible to use the collector to find storage leaks in pro‐
       grams 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.

       The  collector may, on rare occasion produce warning messages.  On UNIX
       machines these appear on stderr.	 Warning  messages  can	 be  filtered,
       redirected,  or	ignored	 with GC_set_warn_proc This is recommended for
       production code.	 See gc.h for details.

       Fully portable code should call GC_INIT from the	 main  program	before
       making any other GC calls.  On most platforms this does nothing and the
       collector is initialized on first use.  On  a  few  platforms  explicit
       initialization is necessary.  And it can never hurt.

       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 limited facilities to sup‐
       port 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,  support
       for ``abortable'' garbage collections during idle time, etc.

       The  README  and gc.h files in the distribution.	 More detailed defini‐
       tions of the functions exported by the collector are given there.  (The
       above list is not complete.)

       The web site at http://www.hpl.hp.com/personal/Hans_Boehm/gc .

       Boehm, H., and M. Weiser, "Garbage Collection in an Uncooperative Envi‐
       ronment", Software Practice & Experience, September 1988, pp. 807-820.

       The malloc(3) man page.

       Hans-J. Boehm (Hans.Boehm@hp.com).  Some of the	code  was  written  by
       others, most notably Alan Demers.

				2 October 2003				 gc(3)

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