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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.
GC_INITIAL_HEAP_SIZE=<bytes> - Initial heap size in bytes. May speed up
process start-up.
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_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 .
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.
GC_ALL_INTERIOR_POINTERS - Turns on GC_all_interior_pointers and thus interior
pointer recognition.
GC_DONT_GC - Turns off garbage collection. Use cautiously.
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