文件列表:

gc6.1 (0, 2004-02-23)
gc6.1\reclaim.c (28721, 2002-08-07)
gc6.1\allchblk.c (24331, 2002-04-09)
gc6.1\misc.c (28313, 2002-08-06)
gc6.1\alloc.c (30917, 2002-08-06)
gc6.1\mach_dep.c (20890, 2002-08-01)
gc6.1\os_dep.c (102094, 2002-08-01)
gc6.1\mark_rts.c (17212, 2001-11-15)
gc6.1\headers.c (9926, 2000-09-21)
gc6.1\mark.c (52690, 2002-08-06)
gc6.1\obj_map.c (4604, 2001-02-13)
gc6.1\pcr_interface.c (4678, 2001-03-22)
gc6.1\blacklst.c (9203, 2001-02-07)
gc6.1\finalize.c (26303, 2002-07-27)
gc6.1\new_hblk.c (6893, 2001-08-09)
gc6.1\real_malloc.c (1021, 1999-09-22)
gc6.1\dyn_load.c (32997, 2002-08-07)
gc6.1\dbg_mlc.c (30415, 2002-07-28)
gc6.1\malloc.c (13171, 2002-08-01)
gc6.1\stubborn.c (9054, 2001-04-14)
gc6.1\checksums.c (5686, 2000-07-08)
gc6.1\solaris_threads.c (28076, 2002-06-13)
gc6.1\irix_threads.c (21974, 2002-05-22)
gc6.1\linux_threads.c (61363, 2002-08-06)
gc6.1\typd_mlc.c (27704, 2001-04-19)
gc6.1\ptr_chck.c (9611, 2001-04-19)
gc6.1\mallocx.c (20060, 2002-07-30)
gc6.1\solaris_pthreads.c (4938, 2002-02-26)
gc6.1\gcj_mlc.c (9685, 2002-02-01)
gc6.1\specific.c (4775, 2002-02-20)
gc6.1\gc_dlopen.c (3234, 2001-09-19)
gc6.1\backgraph.c (14471, 2001-11-09)
gc6.1\mips_sgi_mach_dep.S (949, 2001-06-13)
gc6.1\rs6000_mach_dep.s (2486, 2002-02-26)
gc6.1\alpha_mach_dep.S (1770, 2001-06-28)
gc6.1\sparc_mach_dep.S (1736, 2002-01-01)
gc6.1\threadlibs.c (1094, 2002-08-02)
gc6.1\if_mach.c (754, 2001-03-06)
gc6.1\if_not_there.c (660, 2001-03-06)
gc6.1\gc_cpp.cc (1802, 2002-03-19)
... ...

Copyright (c) 1***8, 1***9 Hans-J. Boehm, Alan J. Demers Copyright (c) 1991-1996 by Xerox Corporation. All rights reserved. Copyright (c) 1996-1999 by Silicon Graphics. All rights reserved. Copyright (c) 1999-2001 by Hewlett-Packard Company. All rights reserved. The file linux_threads.c is also Copyright (c) 19*** by Fergus Henderson. All rights reserved. The files Makefile.am, and configure.in are Copyright (c) 2001 by Red Hat Inc. All rights reserved. Several files supporting GNU-style builds are copyrighted by the Free Software Foundation, and carry a different license from that given below. THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED OR IMPLIED. ANY USE IS AT YOUR OWN RISK. Permission is hereby granted to use or copy this program for any purpose, provided the above notices are retained on all copies. Permission to modify the code and to distribute modified code is granted, provided the above notices are retained, and a notice that the code was modified is included with the above copyright notice. A few of the files needed to use the GNU-style build procedure come with slightly different licenses, though they are all similar in spirit. A few are GPL'ed, but with an exception that should cover all uses in the collector. (If you are concerned about such things, I recommend you look at the notice in config.guess or ltmain.sh.) This is version 6.1 of a conservative garbage collector for C and C++. You might find a more recent version of this at http://www.hpl.hp.com/personal/Hans_Boehm/gc OVERVIEW This is intended to be a general purpose, garbage collecting storage allocator. The algorithms used are described in: Boehm, H., and M. Weiser, "Garbage Collection in an Uncooperative Environment", Software Practice & Experience, September 1***8, pp. 807-820. Boehm, H., A. Demers, and S. Shenker, "Mostly Parallel Garbage Collection", Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design and Implementation, SIGPLAN Notices 26, 6 (June 1991), pp. 157-1***. Boehm, H., "Space Efficient Conservative Garbage Collection", Proceedings of the ACM SIGPLAN '91 Conference on Programming Language Design and Implementation, SIGPLAN Notices 28, 6 (June 1993), pp. 197-206. Boehm H., "Reducing Garbage Collector Cache Misses", Proceedings of the 2000 International Symposium on Memory Management. Possible interactions between the collector and optimizing compilers are discussed in Boehm, H., and D. Chase, "A Proposal for GC-safe C Compilation", The Journal of C Language Translation 4, 2 (December 1992). and Boehm H., "Simple GC-safe Compilation", Proceedings of the ACM SIGPLAN '96 Conference on Programming Language Design and Implementation. (Some of these are also available from http://www.hpl.hp.com/personal/Hans_Boehm/papers/, among other places.) Unlike the collector described in the second reference, this collector operates either with the mutator stopped during the entire collection (default) or incrementally during allocations. (The latter is supported on only a few machines.) On the most common platforms, it can be built with or without thread support. On a few platforms, it can take advantage of a multiprocessor to speed up garbage collection. Many of the ideas underlying the collector have previously been explored by others. Notably, some of the run-time systems developed at Xerox PARC in the early 1***0s conservatively scanned thread stacks to locate possible pointers (cf. Paul Rovner, "On Adding Garbage Collection and Runtime Types to a Strongly-Typed Statically Checked, Concurrent Language" Xerox PARC CSL 84-7). Doug McIlroy wrote a simpler fully conservative collector that was part of version 8 UNIX (tm), but appears to not have received widespread use. Rudimentary tools for use of the collector as a leak detector are included (see http://www.hpl.hp.com/personal/Hans_Boehm/gc/leak.html), as is a fairly sophisticated string package "cord" that makes use of the collector. (See doc/README.cords and H.-J. Boehm, R. Atkinson, and M. Plass, "Ropes: An Alternative to Strings", Software Practice and Experience 25, 12 (December 1995), pp. 1315-1330. This is very similar to the "rope" package in Xerox Cedar, or the "rope" package in the SGI STL or the g++ distribution.) Further collector documantation can be found at http://www.hpl.hp.com/personal/Hans_Boehm/gc GENERAL DESCRIPTION This is a garbage collecting storage allocator that is intended to be used as a plug-in replacement for C's malloc. Since the collector does not require pointers to be tagged, it does not attempt to ensure that all inaccessible storage is reclaimed. However, in our experience, it is typically more successful at reclaiming unused memory than most C programs using explicit deallocation. Unlike manually introduced leaks, the amount of unreclaimed memory typically stays bounded. In the following, an "object" is defined to be a region of memory allocated by the routines described below. Any objects not intended to be collected must be pointed to either from other such accessible objects, or from the registers, stack, data, or statically allocated bss segments. Pointers from the stack or registers may point to anywhere inside an object. The same is true for heap pointers if the collector is compiled with ALL_INTERIOR_POINTERS defined, as is now the default. Compiling without ALL_INTERIOR_POINTERS may reduce accidental retention of garbage objects, by requiring pointers from the heap to to the beginning of an object. But this no longer appears to be a significant issue for most programs. There are a number of routines which modify the pointer recognition algorithm. GC_register_displacement allows certain interior pointers to be recognized even if ALL_INTERIOR_POINTERS is nor defined. GC_malloc_ignore_off_page allows some pointers into the middle of large objects to be disregarded, greatly reducing the probablility of accidental retention of large objects. For most purposes it seems best to compile with ALL_INTERIOR_POINTERS and to use GC_malloc_ignore_off_page if you get collector warnings from allocations of very large objects. See README.debugging for details. WARNING: pointers inside memory allocated by the standard "malloc" are not seen by the garbage collector. Thus objects pointed to only from such a region may be prematurely deallocated. It is thus suggested that the standard "malloc" be used only for memory regions, such as I/O buffers, that are guaranteed not to contain pointers to garbage collectable memory. Pointers in C language automatic, static, or register variables, are correctly recognized. (Note that GC_malloc_uncollectable has semantics similar to standard malloc, but allocates objects that are traced by the collector.) WARNING: the collector does not always know how to find pointers in data areas that are associated with dynamic libraries. This is easy to remedy IF you know how to find those data areas on your operating system (see GC_add_roots). Code for doing this under SunOS, IRIX 5.X and 6.X, HP/UX, Alpha OSF/1, Linux, and win32 is included and used by default. (See README.win32 for win32 details.) On other systems pointers from dynamic library data areas may not be considered by the collector. If you're writing a program that depends on the collector scanning dynamic library data areas, it may be a good idea to include at least one call to GC_is_visible() to ensure that those areas are visible to the collector. Note that the garbage collector does not need to be informed of shared read-only data. However if the shared library mechanism can introduce discontiguous data areas that may contain pointers, then the collector does need to be informed. Signal processing for most signals may be deferred during collection, and during uninterruptible parts of the allocation process. Like standard ANSI C mallocs, by default it is unsafe to invoke malloc (and other GC routines) from a signal handler while another malloc call may be in progress. Removing -DNO_SIGNALS from Makefile attempts to remedy that. But that may not be reliable with a compiler that substantially reorders memory operations inside GC_malloc. The allocator/collector can also be configured for thread-safe operation. (Full signal safety can also be achieved, but only at the cost of two system calls per malloc, which is usually unacceptable.) WARNING: the collector does not guarantee to scan thread-local storage (e.g. of the kind accessed with pthread_getspecific()). The collector does scan thread stacks, though, so generally the best solution is to ensure that any pointers stored in thread-local storage are also stored on the thread's stack for the duration of their lifetime. (This is arguably a longstanding bug, but it hasn't been fixed yet.) INSTALLATION AND PORTABILITY As distributed, the macro SILENT is defined in Makefile. In the event of problems, this can be removed to obtain a moderate amount of descriptive output for each collection. (The given statistics exhibit a few peculiarities. Things don't appear to add up for a variety of reasons, most notably fragmentation losses. These are probably much more significant for the contrived program "test.c" than for your application.) Note that typing "make test" will automatically build the collector and then run setjmp_test and gctest. Setjmp_test will give you information about configuring the collector, which is useful primarily if you have a machine that's not already supported. Gctest is a somewhat superficial test of collector functionality. Failure is indicated by a core dump or a message to the effect that the collector is broken. Gctest takes about 35 seconds to run on a SPARCstation 2. It may use up to 8 MB of memory. (The multi-threaded version will use more. ***-bit versions may use more.) "Make test" will also, as its last step, attempt to build and test the "cord" string library. This will fail without an ANSI C compiler, but the garbage collector itself should still be usable. The Makefile will generate a library gc.a which you should link against. Typing "make cords" will add the cord library to gc.a. Note that this requires an ANSI C compiler. It is suggested that if you need to replace a piece of the collector (e.g. GC_mark_rts.c) you simply list your version ahead of gc.a on the ld command line, rather than replacing the one in gc.a. (This will generate numerous warnings under some versions of AIX, but it still works.) All include files that need to be used by clients will be put in the include subdirectory. (Normally this is just gc.h. "Make cords" adds "cord.h" and "ec.h".) The collector currently is designed to run essentially unmodified on machines that use a flat 32-bit or ***-bit address space. That includes the vast majority of Workstations and X86 (X >= 3) PCs. (The list here was deleted because it was getting too long and constantly out of date.) It does NOT run under plain 16-bit DOS or Windows 3.X. There are however various packages (e.g. win32s, djgpp) that allow flat 32-bit address applications to run under those systemsif the have at least an 80386 processor, and several of those are compatible with the collector. In a few cases (Amiga, OS/2, Win32, MacOS) a separate makefile or equivalent is supplied. Many of these have separate README.system files. Dynamic libraries are completely supported only under SunOS/Solaris, (and even that support is not functional on the last Sun 3 release), Linux, FreeBSD, NetBSD, IRIX 5&6, HP/UX, Win32 (not Win32S) and OSF/1 on DEC AXP machines plus perhaps a few others listed near the top of dyn_load.c. On other machines we recommend that you do one of the following: 1) Add dynamic library support (and send us the code). 2) Use static versions of the libraries. 3) Arrange for dynamic libraries to use the standard malloc. This is still dangerous if the library stores a pointer to a garbage collected object. But nearly all standard interfaces prohibit this, because they deal correctly with pointers to stack allocated objects. (Strtok is an exception. Don't use it.) In all cases we assume that pointer alignment is consistent with that enforced by the standard C compilers. If you use a nonstandard compiler you may have to adjust the alignment parameters defined in gc_priv.h. Note that this may also be an issue with packed records/structs, if those enforce less alignment for pointers. A port to a machine that is not byte addressed, or does not use 32 bit or *** bit addresses will require a major effort. A port to plain MSDOS or win16 is hard. For machines not already mentioned, or for nonstandard compilers, the following are likely to require change: 1. The parameters in gcconfig.h. The parameters that will usually require adjustment are STACKBOTTOM, ALIGNMENT and DATASTART. Setjmp_test prints its guesses of the first two. DATASTART should be an expression for computing the address of the beginning of the data segment. This can often be &etext. But some memory management units require that there be some unmapped space between the text and the data segment. Thus it may be more complicated. On UNIX systems, this is rarely documented. But the adb "$m" command may be helpful. (Note that DATASTART will usually be a function of &etext. Thus a single experiment is usually insufficient.) STACKBOTTOM is used to initialize GC_stackbottom, which should be a sufficient approximation to the coldest stack address. On some machines, it is difficult to obtain such a value that is valid across a variety of MMUs, OS releases, etc. A number of alternatives exist for using the collector in spite of this. See the discussion in gcconfig.h immediately preceding the various definitions of STACKBOTTOM. 2. mach_dep.c. The most important routine here is one to mark from registers. The distributed file includes a generic hack (based on setjmp) that happens to work on many machines, and may work on yours. Try compiling and running setjmp_t.c to see whether it has a chance of working. (This is not correct C, so don't blame your compiler if it doesn't work. Based on limited experience, register window machines are likely to cause trouble. If your version of setjmp claims that all accessible variables, including registers, have the value they had at the time of the longjmp, it also will not work. Vanilla 4.2 BSD on Vaxen makes such a claim. SunOS does not.) If your compiler does not allow in-line assembly code, or if you prefer not to use such a facility, mach_dep.c may be replaced by a .s file (as we did for the MIPS machine and the PC/RT). At this point enough architectures are supported by mach_dep.c that you will rarely need to do more than adjust for assembler syntax. 3. os_dep.c (and gc_priv.h). Several kinds of operating system dependent routines reside here. Many are optional. Several are invoked only through corresponding macros in gc_priv.h, which may also be redefined as appropriate. The routine GC_register_data_segments is crucial. It registers static data areas that must be traversed by the collector. (User calls to GC_add_roots may sometimes be used for similar effect.) Routines to obtain memory from the OS also reside here. Alternatively this can be done entirely by the macro GET_MEM defined in gc_priv.h. Routines to disable and reenable signals also reside here if they are need by the macros DISABLE_SIGNALS and ENABLE_SIGNALS defined in gc_priv.h. In a multithreaded environment, the macros LOCK and UNLOCK in gc_priv.h will need to be suitably redefined. The incremental collector requires page dirty information, which is acquired through routines defined in os_dep.c. Unless directed otherwise by gcconfig.h, these are implemented as stubs that simply treat all pages as dirty. (This of course makes the incremental collector much less useful.) 4. dyn_load.c This provides a routine that allows the collector to scan data segments associated with dynamic libraries. Often it is not necessary to provide this routine unless user-written dynamic libraries are used. For a different version of UN*X or different machines using the Motorola 68000, Vax, SPARC, 80386, NS 32000, PC/RT, or MIPS architecture, it should frequently suffice to change definitions in gcconfig.h. THE C INTERFACE TO THE ALLOCATOR The following routines are intended to be directly called by the user. Note that usually only GC_malloc is necessary. GC_clear_roots and GC_add_roots calls may be required if the collector has to trace from nonstandard places (e.g. from dynamic library data areas on a machine on which the collector doesn't already understand them.) On some machines, it may be desirable to set GC_stacktop to a good approximation of the stack base. (This enhances code portability on HP PA machines, since there is no good way for the collector to compute this value.) Client code may include "gc.h", which defines all of the following, plus many others. 1) GC_malloc(nbytes) - allocate an object of size nbytes. Unlike malloc, the object is cleared before being returned to the user. Gc_malloc will invoke the garbage collector when it determines this to be appropriate. GC_malloc may return 0 if it is unable to acquire sufficient space from the operating system. This is the most probable consequence of running out of space. Other possible consequences are that a function call will fail due to lack of stack space, or that the collector will fail in other ways because it cannot maintain its internal data structures, or that a crucial system process will fail and take down the machine. Most of these possibilities are independent of the malloc implementation. 2) GC_malloc_atomic(nbytes) - allocate an object of size nbytes that is guaranteed not to contain any pointers. The returned object is not guaranteed to be cleared. (Can always be replaced by GC_malloc, but results in faster collection times. The collector will probably run faster if large character arrays, etc. are allocated with GC_malloc_atomic than if they are statically allocated.) 3) GC_realloc(object, new_size) - change the size of object to be new_size. Returns a pointer to the new object, which may, or may not, be the same as the pointer to the old object. The new object is taken to be atomic iff the old one was. If the new object is composite and larger than the original object, then the newly added bytes are cleared (we hope). This is very likely to allocate a new object, unless MERGE_SIZES is defined in gc_priv.h. Even then, it is likely to recycle the old object only if the object is grown in small additive increments (which, we claim, is generally bad coding practice.) 4) GC_free(object) - explicitly deallocate an object returned by GC_malloc or GC_malloc_atomic. Not necessary, but can be used to minimize collections if performance is critical. Probably a performance loss for very small objects (<= 8 bytes). 5) GC_expand_hp(bytes) - Explicitly increase the heap size. (This is normally done automatically i ... ...

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