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diff --git a/pthreads/BUGS b/pthreads/BUGS new file mode 100644 index 000000000..29cee0033 --- /dev/null +++ b/pthreads/BUGS @@ -0,0 +1,133 @@ +---------- +Known bugs +---------- + +1. Not strictly a bug, more of a gotcha. + + Under MS VC++ (only tested with version 6.0), a term_func + set via the standard C++ set_terminate() function causes the + application to abort. + + Notes from the MSVC++ manual: + 1) A term_func() should call exit(), otherwise + abort() will be called on return to the caller. + A call to abort() raises SIGABRT and the default signal handler + for all signals terminates the calling program with + exit code 3. + 2) A term_func() must not throw an exception. Therefore + term_func() should not call pthread_exit(), which + works by throwing an exception (pthreadVCE or pthreadVSE) + or by calling longjmp (pthreadVC). + + Workaround: avoid using pthread_exit() in C++ applications. Exit + threads by dropping through the end of the thread routine. + +2. Cancellation problems in optimised code + - Milan Gardian + + This is suspected to be a compiler bug in VC6.0, and also seen in + VC7.0 and VS .NET 2003. The GNU C++ compiler does not have a problem + with this, and it has been reported that the Intel C++ 8.1 compiler + and Visual C++ 2005 Express Edition Beta2 pass tests\semaphore4.c + (which exposes the bug). + + Workaround [rpj - 2 Feb 2002] + ----------------------------- + [Please note: this workaround did not solve a similar problem in + snapshot-2004-11-03 or later, even though similar symptoms were seen. + tests\semaphore4.c fails in that snapshot for the VCE version of the + DLL.] + + The problem disappears when /Ob0 is used, i.e. /O2 /Ob0 works OK, + but if you want to use inlining optimisation you can be much more + specific about where it's switched off and on by using a pragma. + + So the inlining optimisation is interfering with the way that cleanup + handlers are run. It appears to relate to auto-inlining of class methods + since this is the only auto inlining that is performed at /O1 optimisation + (functions with the "inline" qualifier are also inlined, but the problem + doesn't appear to involve any such functions in the library or testsuite). + + In order to confirm the inlining culprit, the following use of pragmas + eliminate the problem but I don't know how to make it transparent, putting + it in, say, pthread.h where pthread_cleanup_push defined as a macro. + + #pragma inline_depth(0) + pthread_cleanup_push(handlerFunc, (void *) &arg); + + /* ... */ + + pthread_cleanup_pop(0); + #pragma inline_depth() + + Note the empty () pragma value after the pop macro. This resets depth to the + default. Or you can specify a non-zero depth here. + + The pragma is also needed (and now used) within the library itself wherever + cleanup handlers are used (condvar.c and rwlock.c). + + Use of these pragmas allows compiler optimisations /O1 and /O2 to be + used for either or both the library and applications. + + Experimenting further, I found that wrapping the actual cleanup handler + function with #pragma auto_inline(off|on) does NOT work. + + MSVC6.0 doesn't appear to support the C99 standard's _Pragma directive, + however, later versions may. This form is embeddable inside #define + macros, which would be ideal because it would mean that it could be added + to the push/pop macro definitions in pthread.h and hidden from the + application programmer. + + [/rpj] + + Original problem description + ---------------------------- + + The cancellation (actually, cleanup-after-cancel) tests fail when using VC + (professional) optimisation switches (/O1 or /O2) in pthreads library. I + have not investigated which concrete optimisation technique causes this + problem (/Og, /Oi, /Ot, /Oy, /Ob1, /Gs, /Gf, /Gy, etc.), but here is a + summary of builds and corresponding failures: + + * pthreads VSE (optimised tests): OK + * pthreads VCE (optimised tests): Failed "cleanup1" test (runtime) + + * pthreads VSE (DLL in CRT, optimised tests): OK + * pthreads VCE (DLL in CRT, optimised tests): Failed "cleanup1" test + (runtime) + + Please note that while in VSE version of the pthreads library the + optimisation does not really have any impact on the tests (they pass OK), in + VCE version addition of optimisation (/O2 in this case) causes the tests to + fail uniformly - either in "cleanup0" or "cleanup1" test cases. + + Please note that all the tests above use default pthreads DLL (no + optimisations, linked with either static or DLL CRT, based on test type). + Therefore the problem lies not within the pthreads DLL but within the + compiled client code (the application using pthreads -> involvement of + "pthread.h"). + + I think the message of this section is that usage of VCE version of pthreads + in applications relying on cancellation/cleanup AND using optimisations for + creation of production code is highly unreliable for the current version of + the pthreads library. + +3. The Borland Builder 5.5 version of the library produces memory read exceptions +in some tests. + +4. pthread_barrier_wait() can deadlock if the number of potential calling +threads for a particular barrier is greater than the barrier count parameter +given to pthread_barrier_init() for that barrier. + +This is due to the very lightweight implementation of pthread-win32 barriers. +To cope with more than "count" possible waiters, barriers must effectively +implement all the same safeguards as condition variables, making them much +"heavier" than at present. + +The workaround is to ensure that no more than "count" threads attempt to wait +at the barrier. + +5. Canceling a thread blocked on pthread_once appears not to work in the MSVC++ +version of the library "pthreadVCE.dll". The test case "once3.c" hangs. I have no +clues on this at present. All other versions pass this test ok - pthreadsVC.dll, +pthreadsVSE.dll, pthreadsGC.dll and pthreadsGCE.dll. |