1 The garbage collector looks at a number of environment variables which are
2 then used to affect its operation. These are examined only on Un*x-like
5 GC_INITIAL_HEAP_SIZE=<bytes> - Initial heap size in bytes. May speed up
8 GC_MAXIMUM_HEAP_SIZE=<bytes> - Maximum collected heap size.
10 GC_LOOP_ON_ABORT - Causes the collector abort routine to enter a tight loop.
11 This may make it easier to debug, such a process, especially
12 for multithreaded platforms that don't produce usable core
13 files, or if a core file would be too large. On some
14 platforms, this also causes SIGSEGV to be caught and
15 result in an infinite loop in a handler, allowing
16 similar debugging techniques.
18 GC_PRINT_STATS - Turn on GC logging. Not functional with -DSMALL_CONFIG.
20 GC_LOG_FILE - The name of the log file. Stderr by default.
22 GC_PRINT_VERBOSE_STATS - Turn on even more logging.
24 GC_DUMP_REGULARLY - Generate a GC debugging dump GC_dump() on startup
25 and during every collection. Very verbose. Useful
26 if you have a bug to report, but please include only the
29 GC_BACKTRACES=<n> - Generate n random backtraces (for heap profiling) after
30 each GC. Collector must have been built with
31 KEEP_BACK_PTRS. This won't generate useful output unless
32 most objects in the heap were allocated through debug
33 allocators. This is intended to be only a statistical
34 sample; individual traces may be erroneous due to
35 concurrent heap mutation.
37 GC_PRINT_ADDRESS_MAP - Linux only. Dump /proc/self/maps, i.e. various address
38 maps for the process, to stderr on every GC. Useful for
39 mapping root addresses to source for deciphering leak
42 GC_NPROCS=<n> - Linux w/threads only. Explicitly sets the number of processors
43 that the GC should expect to use. Note that setting this to 1
44 when multiple processors are available will preserve
45 correctness, but may lead to really horrible performance,
46 since the lock implementation will immediately yield without
49 GC_MARKERS=<n> - Linux w/threads and parallel marker only. Set the number
50 of marker threads. This is normally set to the number of
51 processors. It is safer to adjust GC_MARKERS than GC_NPROCS,
52 since GC_MARKERS has no impact on the lock implementation.
54 GC_NO_BLACKLIST_WARNING - Prevents the collector from issuing
55 warnings about allocations of very large blocks.
56 Deprecated. Use GC_LARGE_ALLOC_WARN_INTERVAL instead.
58 GC_LARGE_ALLOC_WARN_INTERVAL=<n> - Print every nth warning about very large
59 block allocations, starting with the nth one. Small values
60 of n are generally benign, in that a bounded number of
61 such warnings generally indicate at most a bounded leak.
62 For best results it should be set at 1 during testing.
63 Default is 5. Very large numbers effectively disable the
66 GC_IGNORE_GCJ_INFO - Ignore the type descriptors implicitly supplied by
67 GC_gcj_malloc and friends. This is useful for debugging
68 descriptor generation problems, and possibly for
69 temporarily working around such problems. It forces a
70 fully conservative scan of all heap objects except
71 those known to be pointerfree, and may thus have other
74 GC_PRINT_BACK_HEIGHT - Print max length of chain through unreachable objects
75 ending in a reachable one. If this number remains
76 bounded, then the program is "GC robust". This ensures
77 that a fixed number of misidentified pointers can only
78 result in a bounded space leak. This currently only
79 works if debugging allocation is used throughout.
80 It increases GC space and time requirements appreciably.
81 This feature is still somewhat experimental, and requires
82 that the collector have been built with MAKE_BACK_GRAPH
83 defined. For details, see Boehm, "Bounding Space Usage
84 of Conservative Garbage Collectors", POPL 2001, or
85 http://lib.hpl.hp.com/techpubs/2001/HPL-2001-251.html .
87 GC_RETRY_SIGNALS, GC_NO_RETRY_SIGNALS - Try to compensate for lost
88 thread suspend signals in linux_threads.c. On by
89 default for GC_OSF1_THREADS, off otherwise. Note
90 that this does not work around a possible loss of
91 thread restart signals. This seems to be necessary for
92 some versions of Tru64. Since we've previously seen
93 similar issues on some other operating systems, it
94 was turned into a runtime flag to enable last-minute
97 The following turn on runtime flags that are also program settable. Checked
98 only during initialization. We expect that they will usually be set through
99 other means, but this may help with debugging and testing:
101 GC_ENABLE_INCREMENTAL - Turn on incremental collection at startup. Note that,
102 depending on platform and collector configuration, this
103 may involve write protecting pieces of the heap to
104 track modifications. These pieces may include pointerfree
105 objects or not. Although this is intended to be
106 transparent, it may cause unintended system call failures.
109 GC_PAUSE_TIME_TARGET - Set the desired garbage collector pause time in msecs.
110 This only has an effect if incremental collection is
111 enabled. If a collection requires appreciably more time
112 than this, the client will be restarted, and the collector
113 will need to do additional work to compensate. The
114 special value "999999" indicates that pause time is
115 unlimited, and the incremental collector will behave
116 completely like a simple generational collector. If
117 the collector is configured for parallel marking, and
118 run on a multiprocessor, incremental collection should
119 only be used with unlimited pause time.
121 GC_FIND_LEAK - Turns on GC_find_leak and thus leak detection. Forces a
122 collection at program termination to detect leaks that would
123 otherwise occur after the last GC.
125 GC_ALL_INTERIOR_POINTERS - Turns on GC_all_interior_pointers and thus interior
128 GC_DONT_GC - Turns off garbage collection. Use cautiously.
130 GC_TRACE=addr - Intended for collector debugging. Requires that the collector
131 have been built with ENABLE_TRACE defined. Causes the debugger
132 to log information about the tracing of address ranges containing
133 addr. Typically addr is the address that contains a pointer to
134 an object that mysteriously failed to get marked. Addr must be
135 specified as a hexadecimal integer.