71 lines
3.8 KiB
Plaintext
71 lines
3.8 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 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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Note:
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Before you run "make check", you need to set your LD_LIBRARY_PATH correctly
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(e.g., to "/usr/local/lib") so that tests can find the shared library
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libgcc_s.so.1. Alternatively, you can configure with --disable-shared.
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SOLARIS THREADS:
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Unless --disable-threads option is given, threads support is on by default in
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configure. This causes the collector to be compiled with -D GC_THREADS
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ensuring thread safety. This assumes use of the pthread_ interface; old-style
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Solaris threads are no longer supported.
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Thread-local allocation is now on by default. Parallel marking is on by
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default starting from GC v7.3 but it could be disabled manually
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by configure --disable-parallel-mark option.
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It is also essential that gc.h be included in files that call pthread_create,
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pthread_join, pthread_detach, or dlopen. gc.h macro defines these to also do
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GC bookkeeping, etc. gc.h must be included with one or both of these macros
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defined, otherwise these replacements are not visible. A collector built in
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this way way only be used by programs that are linked with the threads library.
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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 threads are used on an X86 processor with malloc redirected to
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GC_malloc, it is necessary to call GC_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 SEGV faults. 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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I encountered "symbol <unknown>: offset .... is non-aligned" errors. These
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appear to be traceable to the use of the GNU assembler with the Sun linker.
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The former appears to generate a relocation not understood by the latter.
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The fix appears to be to use a consistent tool chain. (As a non-Solaris-expert
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my solution involved hacking the libtool script, but I'm sure you can
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do something less ugly.)
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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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