+The collector supports both incremental collection and threads under
+Solaris 2. The incremental collector normally retrieves page dirty information
+through the appropriate /proc calls. But it can also be configured
+(by defining MPROTECT_VDB instead of PROC_VDB in gcconfig.h) to use mprotect
+and signals. This may result in shorter pause times, but it is no longer
+safe to issue arbitrary system calls that write to the heap.
+
+Under other UNIX versions,
+the collector normally obtains memory through sbrk. There is some reason
+to expect that this is not safe if the client program also calls the system
+malloc, or especially realloc. The sbrk man page strongly suggests this is
+not safe: "Many library routines use malloc() internally, so use brk()
+and sbrk() only when you know that malloc() definitely will not be used by
+any library routine." This doesn't make a lot of sense to me, since there
+seems to be no documentation as to which routines can transitively call malloc.
+Nonetheless, under Solaris2, the collector now allocates
+memory using mmap by default. (It defines USE_MMAP in gcconfig.h.)
+You may want to reverse this decisions if you use -DREDIRECT_MALLOC=...
+
+Note:
+Before you run "make check", you need to set your LD_LIBRARY_PATH correctly
+(eg., to "/usr/local/lib") so that tests can find the shared library
+libgcc_s.so.1. Alternatively, you can configure with --disable-shared.
+
+SOLARIS THREADS:
+
+Threads support is enabled by configure "--enable-threads=posix" option.
+(In case of GCC compiler, multi-threading support is on by default.)
+This causes the collector to be compiled with -D GC_THREADS (or
+-D GC_SOLARIS_THREADS) ensuring thread safety.
+This assumes use of the pthread_ interface. Old style Solaris threads
+are no longer supported.
+Thread-local allocation is now on by default. Parallel marking is on by
+default starting from GC v7.3 but it could be enabled or disabled manually
+by the corresponding "--enable/disable-parallel-mark" options.
+
+It is also essential that gc.h be included in files that call pthread_create,
+pthread_join, pthread_detach, or dlopen. gc.h macro defines these to also do
+GC bookkeeping, etc. gc.h must be included with one or both of these macros
+defined, otherwise these replacements are not visible. A collector built in
+this way way only be used by programs that are linked with the threads library.
+
+Since 5.0 alpha5, dlopen disables collection temporarily,
+unless USE_PROC_FOR_LIBRARIES is defined. In some unlikely cases, this
+can result in unpleasant heap growth. But it seems better than the
+race/deadlock issues we had before.
+
+If threads are used on an X86 processor with malloc redirected to
+GC_malloc, it is necessary to call GC_INIT explicitly before forking the
+first thread. (This avoids a deadlock arising from calling GC_thr_init
+with the allocation lock held.)
+
+It appears that there is a problem in using gc_cpp.h in conjunction with
+Solaris threads and Sun's C++ runtime. Apparently the overloaded new operator
+is invoked by some iostream initialization code before threads are correctly
+initialized. As a result, call to thr_self() in garbage collector
+initialization SEGV faults. Currently the only known workaround is to not
+invoke the garbage collector from a user defined global operator new, or to
+have it invoke the garbage-collector's allocators only after main has started.
+(Note that the latter requires a moderately expensive test in operator
+delete.)
+
+I encountered "symbol <unknown>: offet .... is non-aligned" errors. These
+appear to be traceable to the use of the GNU assembler with the Sun linker.
+The former appears to generate a relocation not understood by the latter.
+The fix appears to be to use a consistent tool chain. (As a non-Solaris-expert
+my solution involved hacking the libtool script, but I'm sure you can
+do something less ugly.)
+
+Hans-J. Boehm
+(The above contains my personal opinions, which are probably not shared
+by anyone else.)
projects / hs-boehmgc.git / blobdiff