diff options
Diffstat (limited to '')
| -rw-r--r-- | gc/doc/README.solaris2 | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/gc/doc/README.solaris2 b/gc/doc/README.solaris2 new file mode 100644 index 0000000..6ed61dc --- /dev/null +++ b/gc/doc/README.solaris2 @@ -0,0 +1,62 @@ +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 (since 4.12) 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=... + + +SOLARIS THREADS: + +The collector must be compiled with -DGC_SOLARIS_THREADS (thr_ functions) +or -DGC_SOLARIS_PTHREADS (pthread_ functions) to be thread safe. +It is also essential that gc.h be included in files that call thr_create, +thr_join, thr_suspend, thr_continue, 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. + +In this mode, the collector contains various workarounds for older Solaris +bugs. Mostly, these should not be noticeable unless you look at system +call traces. However, it cannot protect a guard page at the end of +a thread stack. If you know that you will only be running Solaris2.5 +or later, it should be possible to fix this by compiling the collector +with -DSOLARIS23_MPROTECT_BUG_FIXED. + +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 solaris_threads are used on an X86 processor with malloc redirected to +GC_malloc, it is necessary to call GC_thr_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 segfaults. 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.) + +Hans-J. Boehm +(The above contains my personal opinions, which are probably not shared +by anyone else.) |