| 1 | The garbage collector looks at a number of environment variables which are
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| 2 | then used to affect its operation. These are examined only on Un*x-like
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| 3 | platforms.
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| 4 |
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| 5 | GC_INITIAL_HEAP_SIZE=<bytes> - Initial heap size in bytes. May speed up
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| 6 | process start-up.
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| 7 |
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| 8 | GC_LOOP_ON_ABORT - Causes the collector abort routine to enter a tight loop.
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| 9 | This may make it easier to debug, such a process, especially
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| 10 | for multithreaded platforms that don't produce usable core
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| 11 | files, or if a core file would be too large. On some
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| 12 | platforms, this also causes SIGSEGV to be caught and
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| 13 | result in an infinite loop in a handler, allowing
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| 14 | similar debugging techniques.
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| 15 |
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| 16 | GC_PRINT_STATS - Turn on as much logging as is easily feasible without
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| 17 | adding signifcant runtime overhead. Doesn't work if
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| 18 | the collector is built with SMALL_CONFIG. Overridden
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| 19 | by setting GC_quiet. On by default if the collector
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| 20 | was built without -DSILENT.
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| 21 |
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| 22 | GC_PRINT_ADDRESS_MAP - Linux only. Dump /proc/self/maps, i.e. various address
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| 23 | maps for the process, to stderr on every GC. Useful for
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| 24 | mapping root addresses to source for deciphering leak
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| 25 | reports.
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| 26 |
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| 27 | GC_NPROCS=<n> - Linux w/threads only. Explicitly sets the number of processors
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| 28 | that the GC should expect to use. Note that setting this to 1
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| 29 | when multiple processors are available will preserve
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| 30 | correctness, but may lead to really horrible performance.
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| 31 |
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| 32 | GC_NO_BLACKLIST_WARNING - Prevents the collector from issuing
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| 33 | warnings about allocations of very large blocks.
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| 34 | Deprecated. Use GC_LARGE_ALLOC_WARN_INTERVAL instead.
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| 35 |
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| 36 | GC_LARGE_ALLOC_WARN_INTERVAL=<n> - Print every nth warning about very large
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| 37 | block allocations, starting with the nth one. Small values
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| 38 | of n are generally benign, in that a bounded number of
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| 39 | such warnings generally indicate at most a bounded leak.
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| 40 | For best results it should be set at 1 during testing.
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| 41 | Default is 5. Very large numbers effectively disable the
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| 42 | warning.
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| 43 |
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| 44 | GC_IGNORE_GCJ_INFO - Ignore the type descriptors implicitly supplied by
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| 45 | GC_gcj_malloc and friends. This is useful for debugging
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| 46 | descriptor generation problems, and possibly for
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| 47 | temporarily working around such problems. It forces a
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| 48 | fully conservative scan of all heap objects except
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| 49 | those known to be pointerfree, and may thus have other
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| 50 | adverse effects.
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| 51 |
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| 52 | GC_PRINT_BACK_HEIGHT - Print max length of chain through unreachable objects
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| 53 | ending in a reachable one. If this number remains
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| 54 | bounded, then the program is "GC robust". This ensures
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| 55 | that a fixed number of misidentified pointers can only
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| 56 | result in a bounded space leak. This currently only
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| 57 | works if debugging allocation is used throughout.
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| 58 | It increases GC space and time requirements appreciably.
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| 59 | This feature is still somewhat experimental, and requires
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| 60 | that the collector have been built with MAKE_BACK_GRAPH
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| 61 | defined. For details, see Boehm, "Bounding Space Usage
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| 62 | of Conservative Garbage Collectors", POPL 2001, or
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| 63 | http://lib.hpl.hp.com/techpubs/2001/HPL-2001-251.html .
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| 64 |
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| 65 | GC_ENABLE_INCREMENTAL - Turn on incremental collection at startup. Note that,
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| 66 | depending on platform and collector configuration, this
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| 67 | may involve write protecting pieces of the heap to
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| 68 | track modifications. These pieces may include pointerfree
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| 69 | objects or not. Although this is intended to be
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| 70 | transparent, it may cause unintended system call failures.
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| 71 | Use with caution.
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| 72 |
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| 73 | GC_PAUSE_TIME_TARGET - Set the desired garbage collector pause time in msecs.
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| 74 | This only has an effect if incremental collection is enabled.
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| 75 | If a collection requires appreciably more time than this,
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| 76 | the client will be restarted, and the collector will need
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| 77 | to do additional work to compensate. The special value
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| 78 | "999999" indicates that pause time is unlimited, and the
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| 79 | incremental collector will behave completely like a
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| 80 | simple generational collector. If the collector is
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| 81 | configured for parallel marking, and run on a multiprocessor,
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| 82 | incremental collection should only be used with unlimited
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| 83 | pause time.
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| 84 |
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| 85 | The following turn on runtime flags that are also program settable. Checked
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| 86 | only during initialization. We expect that they will usually be set through
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| 87 | other means, but this may help with debugging and testing:
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| 88 |
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| 89 | GC_FIND_LEAK - Turns on GC_find_leak and thus leak detection.
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| 90 |
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| 91 | GC_ALL_INTERIOR_POINTERS - Turns on GC_all_interior_pointers and thus interior
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| 92 | pointer recognition.
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| 93 |
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| 94 | GC_DONT_GC - Turns off garbage collection. Use cautiously.
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