path: root/arch/sh/pthread_arch.h
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authorRich Felker <>2014-08-17 22:09:47 -0400
committerRich Felker <>2014-08-17 22:09:47 -0400
commit37195db8ec31300a87bc7ec09d2adcf299e9203d (patch)
treef3d2bbb1ced5199a695a03bfb4d42ba06b7bc8a7 /arch/sh/pthread_arch.h
parent4220d298ef7a2226b14fe4b481f7f7699eab6e3f (diff)
redesign cond var implementation to fix multiple issues
the immediate issue that was reported by Jens Gustedt and needed to be fixed was corruption of the cv/mutex waiter states when switching to using a new mutex with the cv after all waiters were unblocked but before they finished returning from the wait function. self-synchronized destruction was also handled poorly and may have had race conditions. and the use of sequence numbers for waking waiters admitted a theoretical missed-wakeup if the sequence number wrapped through the full 32-bit space. the new implementation is largely documented in the comments in the source. the basic principle is to use linked lists initially attached to the cv object, but detachable on signal/broadcast, made up of nodes residing in automatic storage (stack) on the threads that are waiting. this eliminates the need for waiters to access the cv object after they are signaled, and allows us to limit wakeup to one waiter at a time during broadcasts even when futex requeue cannot be used. performance is also greatly improved, roughly double some tests. basically nothing is changed in the process-shared cond var case, where this implementation does not work, since processes do not have access to one another's local storage.
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