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
(e.g., 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:

Unless --disable-threads option is given, threads support is on by default in
configure.  This causes the collector to be compiled with -D GC_THREADS
ensuring thread safety.  This assumes use of the pthread_ interface; old-style
Solaris threads are no longer supported.  Thread-local allocation is on by
default.  Parallel marking is on by default (it could be disabled manually
by configure --disable-parallel-mark option).

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 GC_THREADS macro defined
first, otherwise these replacements are not visible.  A collector built in
this way may only be used by programs that are linked with the threads library.

Unless USE_PROC_FOR_LIBRARIES is defined, dlopen disables collection
temporarily.  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.)

There could be an issue when using gc_cpp.h in conjunction with Solaris
threads and Sun's C++ runtime.  Apparently the overloaded new operator
may be invoked by some iostream initialization code before threads are
correctly initialized.  This may cause a SIGSEGV during initialization
of the garbage collector.  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>: offset .... 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 toolchain.  (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.)
