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-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.