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