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path: root/src/thread/pthread_mutex_lock.c
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2014-09-06use weak symbols for the POSIX functions that will be used by C threadsJens Gustedt-2/+6
The intent of this is to avoid name space pollution of the C threads implementation. This has two sides to it. First we have to provide symbols that wouldn't pollute the name space for the C threads implementation. Second we have to clean up some internal uses of POSIX functions such that they don't implicitly drag in such symbols.
2014-08-15make futex operations use private-futex mode when possibleRich Felker-1/+2
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.
2011-08-07add fast path for normal mutexes back to pthread_mutex_lockRich Felker-0/+3
2011-08-02avoid accessing mutex memory after atomic unlockRich Felker-13/+1
this change is needed to fix a race condition and ensure that it's possible to unlock and destroy or unmap the mutex as soon as pthread_mutex_lock succeeds. POSIX explicitly gives such an example in the rationale and requires an implementation to allow such usage.
2011-04-14cheap trick to further optimize locking normal mutexesRich Felker-1/+1
2011-03-30cheap special-case optimization for normal mutexesRich Felker-0/+4
cycle-level benchmark on atom cpu showed typical pthread_mutex_lock call dropping from ~120 cycles to ~90 cycles with this change. benefit may vary with compiler options and version, but this optimization is very cheap to make and should always help some.
2011-03-17implement robust mutexesRich Felker-3/+3
some of this code should be cleaned up, e.g. using macros for some of the bit flags, masks, etc. nonetheless, the code is believed to be working and correct at this point.
2011-03-17unify lock and owner fields of mutex structureRich Felker-2/+3
this change is necessary to free up one slot in the mutex structure so that we can use doubly-linked lists in the implementation of robust mutexes.
2011-03-16correct error returns for error-checking mutexesRich Felker-1/+5
2011-02-17reorganize pthread data structures and move the definitions to alltypes.hRich Felker-1/+1
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/+9