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Bug 20116: Clarify behaviour of PD->lock.
Add comments to the concurrency notes to clarify the semaphore-like and mutex-like behaviours of PD->lock.
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@ -1,4 +1,10 @@
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2016-04-03 Adhemerval Zanella <adhemerval.zanella@linaro.org>
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2017-05-03 Carlos O'Donell <carlos@redhat.com>
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[BZ #20116]
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* nptl/pthread_create.c: Expand comments to describe
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semaphore-like and mutex-like uses of PD->lock.
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2017-04-03 Adhemerval Zanella <adhemerval.zanella@linaro.org>
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* sysdeps/unix/sysv/linux/epoll_wait.c: New file.
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* sysdeps/unix/sysv/linux/generic/epoll_wait.c: Remove file.
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@ -94,8 +94,17 @@ unsigned int __nptl_nthreads = 1;
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exactly which of the four ownership states we are in and therefore
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what actions can be taken. For example after (2) we cannot read or
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write from PD anymore since the thread may no longer exist and the
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memory may be unmapped. The most complicated cases happen during
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thread startup:
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memory may be unmapped.
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It is important to point out that PD->lock is being used both
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similar to a one-shot semaphore and subsequently as a mutex. The
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lock is taken in the parent to force the child to wait, and then the
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child releases the lock. However, this semaphore-like effect is used
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only for synchronizing the parent and child. After startup the lock
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is used like a mutex to create a critical section during which a
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single owner modifies the thread parameters.
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The most complicated cases happen during thread startup:
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(a) If the created thread is in a detached (PTHREAD_CREATE_DETACHED),
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or joinable (default PTHREAD_CREATE_JOINABLE) state and
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