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path: root/src/thread/pthread_rwlock_timedwrlock.c
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2019-02-16introduce namespace-safe rwlock aliases; use in pthread_key_createRich Felker-2/+4
commit 84d061d5a31c9c773e29e1e2b1ffe8cb9557bc58 inadvertently introduced namespace violations by using the pthread-namespace rwlock functions in pthread_key_create, which is in turn used for C11 tss. fix that and possible future uses of rwlocks elsewhere.
2015-03-02factor cancellation cleanup push/pop out of futex __timedwait functionRich Felker-1/+1
previously, the __timedwait function was optionally a cancellation point depending on whether it was passed a pointer to a cleaup function and context to register. as of now, only one caller actually used such a cleanup function (and it may face removal soon); most callers either passed a null pointer to disable cancellation or a dummy cleanup function. now, __timedwait is never a cancellation point, and __timedwait_cp is the cancellable version. this makes the intent of the calling code more obvious and avoids ugly dummy functions and long argument lists.
2014-08-25refrain from spinning on locks when there is already a waiterRich Felker-1/+1
if there is already a waiter for a lock, spinning on the lock is essentially an attempt to steal it from whichever waiter would obtain it via any priority rules in place, and is therefore undesirable. in the current implementation, there is always an inherent race window at unlock during which a newly-arriving thread may steal the lock from the existing waiters, but we should aim to keep this window minimal rather than enlarging it.
2014-08-25spin before waiting on futex in mutex and rwlock lock operationsRich Felker-0/+7
2014-08-15make futex operations use private-futex mode when possibleRich Felker-1/+1
private-futex uses the virtual address of the futex int directly as the hash key rather than requiring the kernel to resolve the address to an underlying backing for the mapping in which it lies. for certain usage patterns it improves performance significantly. in many places, the code using futex __wake and __wait operations was already passing a correct fixed zero or nonzero flag for the priv argument, so no change was needed at the site of the call, only in the __wake and __wait functions themselves. in other places, especially where the process-shared attribute for a synchronization object was not previously tracked, additional new code is needed. for mutexes, the only place to store the flag is in the type field, so additional bit masking logic is needed for accessing the type. for non-process-shared condition variable broadcasts, the futex requeue operation is unable to requeue from a private futex to a process-shared one in the mutex structure, so requeue is simply disabled in this case by waking all waiters. for robust mutexes, the kernel always performs a non-private wake when the owner dies. in order not to introduce a behavioral regression in non-process-shared robust mutexes (when the owning thread dies), they are simply forced to be treated as process-shared for now, giving correct behavior at the expense of performance. this can be fixed by adding explicit code to pthread_exit to do the right thing for non-shared robust mutexes in userspace rather than relying on the kernel to do it, and will be fixed in this way later. since not all supported kernels have private futex support, the new code detects EINVAL from the futex syscall and falls back to making the call without the private flag. no attempt to cache the result is made; caching it and using the cached value efficiently is somewhat difficult, and not worth the complexity when the benefits would be seen only on ancient kernels which have numerous other limitations and bugs anyway.
2012-09-06use restrict everywhere it's required by c99 and/or posix 2008Rich Felker-1/+1
to deal with the fact that the public headers may be used with pre-c99 compilers, __restrict is used in place of restrict, and defined appropriately for any supported compiler. we also avoid the form [restrict] since older versions of gcc rejected it due to a bug in the original c99 standard, and instead use the form *restrict.
2011-08-03overhaul rwlocks to address several issuesRich Felker-11/+10
like mutexes and semaphores, rwlocks suffered from a race condition where the unlock operation could access the lock memory after another thread successfully obtained the lock (and possibly destroyed or unmapped the object). this has been fixed in the same way it was fixed for other lock types. in addition, the previous implementation favored writers over readers. in the absence of other considerations, that is the best behavior for rwlocks, and posix explicitly allows it. however posix also requires read locks to be recursive. if writers are favored, any attempt to obtain a read lock while a writer is waiting for the lock will fail, causing "recursive" read locks to deadlock. this can be avoided by keeping track of which threads already hold read locks, but doing so requires unbounded memory usage, and there must be a fallback case that favors readers in case memory allocation failed. and all of this must be synchronized. the cost, complexity, and risk of errors in getting it right is too great, so we simply favor readers. tracking of the owner of write locks has been removed, as it was not useful for anything. it could allow deadlock detection, but it's not clear to me that returning EDEADLK (which a buggy program is likely to ignore) is better than deadlocking; at least the latter behavior prevents further data corruption. a correct program cannot invoke this situation anyway. the reader count and write lock state, as well as the "last minute" waiter flag have all been combined into a single atomic lock. this means all state transitions for the lock are atomic compare-and-swap operations. this makes establishing correctness much easier and may improve performance. finally, some code duplication has been cleaned up. more is called for, especially the standard __timedwait idiom repeated in all locks.
2011-08-02unify and overhaul timed futex waitsRich Felker-1/+1
new features: - FUTEX_WAIT_BITSET op will be used for timed waits if available. this saves a call to clock_gettime. - error checking for the timespec struct is now inside __timedwait so it doesn't need to be duplicated everywhere. cond_timedwait still needs to duplicate it to avoid unlocking the mutex, though. - pushing and popping the cancellation handler is delegated to __timedwait, and cancellable/non-cancellable waits are unified.
2011-02-17reorganize pthread data structures and move the definitions to alltypes.hRich Felker-5/+5
this allows sys/types.h to provide the pthread types, as required by POSIX. this design also facilitates forcing ABI-compatible sizes in the arch-specific alltypes.h, while eliminating the need for developers changing the internals of the pthread types to poke around with arch-specific headers they may not be able to test.
2011-02-12initial check-in, version 0.5.0v0.5.0Rich Felker-0/+17