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= - 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= - 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. GC_NO_BLACKLIST_WARNING - Prevents the collector from issuing "Needed to allocate blacklisted block at ..." warnings. 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_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. 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_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.