Date: Thu, 12 Mar 2009 09:10:03 GMT From: Bruce Simpson <bms@incunabulum.net> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/127545: [sysvipc] POSIX (1003.1b) semaphores can become negative Message-ID: <200903120910.n2C9A3ne010479@freefall.freebsd.org>
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The following reply was made to PR kern/127545; it has been noted by GNATS. From: Bruce Simpson <bms@incunabulum.net> To: freebsd-gnats-submit@freebsd.org Cc: Subject: Re: kern/127545: [sysvipc] POSIX (1003.1b) semaphores can become negative Date: Thu, 12 Mar 2009 08:51:57 +0000 I just managed to reproduce this on RELENG_7, and I clearly see the semaphore value becoming negative. I am attempting to track down why Python multiprocessing doesn't work. It looks like it's related to how Python processes hang on FreeBSD when a thread forks a new process. On the other hand, multiprocessing does use POSIX semaphores for synchronization; the Python interpreter's use of this itself is optional, and it tries to emulate it with condition variables and mutexes. jhb@ recently merged some cleanups however they don't have much to do with the issue here, they just make the implementation cleaner.
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