63 lines
3.3 KiB
Plaintext
63 lines
3.3 KiB
Plaintext
The collector supports both incremental collection and threads under
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Solaris 2. The incremental collector normally retrieves page dirty information
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through the appropriate /proc calls. But it can also be configured
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(by defining MPROTECT_VDB instead of PROC_VDB in gcconfig.h) to use mprotect
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and signals. This may result in shorter pause times, but it is no longer
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safe to issue arbitrary system calls that write to the heap.
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Under other UNIX versions,
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the collector normally obtains memory through sbrk. There is some reason
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to expect that this is not safe if the client program also calls the system
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malloc, or especially realloc. The sbrk man page strongly suggests this is
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not safe: "Many library routines use malloc() internally, so use brk()
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and sbrk() only when you know that malloc() definitely will not be used by
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any library routine." This doesn't make a lot of sense to me, since there
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seems to be no documentation as to which routines can transitively call malloc.
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Nonetheless, under Solaris2, the collector now (since 4.12) allocates
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memory using mmap by default. (It defines USE_MMAP in gcconfig.h.)
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You may want to reverse this decisions if you use -DREDIRECT_MALLOC=...
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SOLARIS THREADS:
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The collector must be compiled with -DGC_SOLARIS_THREADS (thr_ functions)
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or -DGC_SOLARIS_PTHREADS (pthread_ functions) to be thread safe.
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It is also essential that gc.h be included in files that call thr_create,
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thr_join, thr_suspend, thr_continue, or dlopen. Gc.h macro defines
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these to also do GC bookkeeping, etc. Gc.h must be included with
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one or both of these macros defined, otherwise
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these replacements are not visible.
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A collector built in this way way only be used by programs that are
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linked with the threads library.
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In this mode, the collector contains various workarounds for older Solaris
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bugs. Mostly, these should not be noticeable unless you look at system
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call traces. However, it cannot protect a guard page at the end of
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a thread stack. If you know that you will only be running Solaris2.5
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or later, it should be possible to fix this by compiling the collector
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with -DSOLARIS23_MPROTECT_BUG_FIXED.
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Since 5.0 alpha5, dlopen disables collection temporarily,
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unless USE_PROC_FOR_LIBRARIES is defined. In some unlikely cases, this
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can result in unpleasant heap growth. But it seems better than the
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race/deadlock issues we had before.
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If solaris_threads are used on an X86 processor with malloc redirected to
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GC_malloc, it is necessary to call GC_thr_init explicitly before forking the
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first thread. (This avoids a deadlock arising from calling GC_thr_init
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with the allocation lock held.)
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It appears that there is a problem in using gc_cpp.h in conjunction with
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Solaris threads and Sun's C++ runtime. Apparently the overloaded new operator
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is invoked by some iostream initialization code before threads are correctly
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initialized. As a result, call to thr_self() in garbage collector
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initialization segfaults. Currently the only known workaround is to not
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invoke the garbage collector from a user defined global operator new, or to
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have it invoke the garbage-collector's allocators only after main has started.
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(Note that the latter requires a moderately expensive test in operator
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delete.)
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Hans-J. Boehm
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(The above contains my personal opinions, which are probably not shared
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by anyone else.)
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