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diff --git a/gcc-4.8.1/boehm-gc/doc/README.environment b/gcc-4.8.1/boehm-gc/doc/README.environment new file mode 100644 index 000000000..686e94825 --- /dev/null +++ b/gcc-4.8.1/boehm-gc/doc/README.environment @@ -0,0 +1,151 @@ +The garbage collector looks at a number of environment variables which are +then used to affect its operation. These are examined only on Un*x-like +platforms and win32. + +GC_INITIAL_HEAP_SIZE=<bytes> - Initial heap size in bytes. May speed up + process start-up. + +GC_MAXIMUM_HEAP_SIZE=<bytes> - Maximum collected heap size. + +GC_LOOP_ON_ABORT - Causes the collector abort routine to enter a tight loop. + This may make it easier to debug, such a process, especially + for multithreaded platforms that don't produce usable core + files, or if a core file would be too large. On some + platforms, this also causes SIGSEGV to be caught and + result in an infinite loop in a handler, allowing + similar debugging techniques. + +GC_PRINT_STATS - Turn on as much logging as is easily feasible without + adding signifcant runtime overhead. Doesn't work if + the collector is built with SMALL_CONFIG. Overridden + by setting GC_quiet. On by default if the collector + was built without -DSILENT. + +GC_DUMP_REGULARLY - Generate a GC debugging dump GC_dump() on startup + and during every collection. Very verbose. Useful + if you have a bug to report, but please include only the + last complete dump. + +GC_BACKTRACES=<n> - Generate n random backtraces (for heap profiling) after + each GC. Collector must have been built with + KEEP_BACK_PTRS. This won't generate useful output unless + most objects in the heap were allocated through debug + allocators. This is intended to be only a statistical + sample; individual traces may be erroneous due to + concurrent heap mutation. + +GC_PRINT_ADDRESS_MAP - Linux only. Dump /proc/self/maps, i.e. various address + maps for the process, to stderr on every GC. Useful for + mapping root addresses to source for deciphering leak + reports. + +GC_NPROCS=<n> - Linux w/threads only. Explicitly sets the number of processors + that the GC should expect to use. Note that setting this to 1 + when multiple processors are available will preserve + correctness, but may lead to really horrible performance, + since the lock implementation will immediately yield without + first spinning. + +GC_MARKERS=<n> - Linux w/threads and parallel marker only. Set the number + of marker threads. This is normaly set to the number of + processors. It is safer to adjust GC_MARKERS than GC_NPROCS, + since GC_MARKERS has no impact on the lock implementation. + +GC_NO_BLACKLIST_WARNING - Prevents the collector from issuing + warnings about allocations of very large blocks. + Deprecated. Use GC_LARGE_ALLOC_WARN_INTERVAL instead. + +GC_LARGE_ALLOC_WARN_INTERVAL=<n> - Print every nth warning about very large + block allocations, starting with the nth one. Small values + of n are generally benign, in that a bounded number of + such warnings generally indicate at most a bounded leak. + For best results it should be set at 1 during testing. + Default is 5. Very large numbers effectively disable the + warning. + +GC_IGNORE_GCJ_INFO - Ignore the type descriptors implicitly supplied by + GC_gcj_malloc and friends. This is useful for debugging + descriptor generation problems, and possibly for + temporarily working around such problems. It forces a + fully conservative scan of all heap objects except + those known to be pointerfree, and may thus have other + adverse effects. + +GC_PRINT_BACK_HEIGHT - Print max length of chain through unreachable objects + ending in a reachable one. If this number remains + bounded, then the program is "GC robust". This ensures + that a fixed number of misidentified pointers can only + result in a bounded space leak. This currently only + works if debugging allocation is used throughout. + It increases GC space and time requirements appreciably. + This feature is still somewhat experimental, and requires + that the collector have been built with MAKE_BACK_GRAPH + defined. For details, see Boehm, "Bounding Space Usage + of Conservative Garbage Collectors", POPL 2001, or + http://lib.hpl.hp.com/techpubs/2001/HPL-2001-251.html . + +GC_RETRY_SIGNALS, GC_NO_RETRY_SIGNALS - Try to compensate for lost + thread suspend signals in linux_threads.c. On by + default for GC_OSF1_THREADS, off otherwise. Note + that this does not work around a possible loss of + thread restart signals. This seems to be necessary for + some versions of Tru64. Since we've previously seen + similar issues on some other operating systems, it + was turned into a runtime flag to enable last-minute + work-arounds. + +GC_IGNORE_FB[=<n>] - (Win32 only.) Try to avoid treating a mapped + frame buffer as part of the root set. Certain (higher end?) + graphics cards seems to result in the graphics memory mapped + into the user address space as writable memory. + Unfortunately, there seems to be no systematic way to + identify such memory. Setting the environment variable to n + causes the collector to ignore mappings longer than n MB. + The default value of n is currently 15. (This should cover + a 16 MB graphics card, since the mapping appears to be slightly + shorter than all of graphics memory. It will fail if a dll + writes pointers to collectable objects into a data segment + whose length is >= 15MB. Empirically that's rare, but + certainly possible.) WARNING: Security sensitive applications + should probably disable this feature by setting + GC_disallow_ignore_fb, or by building with -DNO_GETENV, + since small values could force collection of reachable + objects, which is conceivably a (difficult to exploit) + security hole. GC_IGNORE_FB values less than 3 MB + are never honored, eliminating this risk for most, + but not all, applications. This feature is likely to disappear + if/when we find a less disgusting "solution". + IN VERSION 6.4 AND LATER, THIS SHOULD BE UNNECESSARY. + +The following turn on runtime flags that are also program settable. Checked +only during initialization. We expect that they will usually be set through +other means, but this may help with debugging and testing: + +GC_ENABLE_INCREMENTAL - Turn on incremental collection at startup. Note that, + depending on platform and collector configuration, this + may involve write protecting pieces of the heap to + track modifications. These pieces may include pointerfree + objects or not. Although this is intended to be + transparent, it may cause unintended system call failures. + Use with caution. + +GC_PAUSE_TIME_TARGET - Set the desired garbage collector pause time in msecs. + This only has an effect if incremental collection is + enabled. If a collection requires appreciably more time + than this, the client will be restarted, and the collector + will need to do additional work to compensate. The + special value "999999" indicates that pause time is + unlimited, and the incremental collector will behave + completely like a simple generational collector. If + the collector is configured for parallel marking, and + run on a multiprocessor, incremental collection should + only be used with unlimited pause time. + +GC_FIND_LEAK - Turns on GC_find_leak and thus leak detection. Forces a + collection at program termination to detect leaks that would + otherwise occur after the last GC. + +GC_ALL_INTERIOR_POINTERS - Turns on GC_all_interior_pointers and thus interior + pointer recognition. + +GC_DONT_GC - Turns off garbage collection. Use cautiously. |