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Diffstat (limited to 'nptl/DESIGN-rwlock.txt')
-rw-r--r-- | nptl/DESIGN-rwlock.txt | 113 |
1 files changed, 0 insertions, 113 deletions
diff --git a/nptl/DESIGN-rwlock.txt b/nptl/DESIGN-rwlock.txt deleted file mode 100644 index 810d1b8f35..0000000000 --- a/nptl/DESIGN-rwlock.txt +++ /dev/null @@ -1,113 +0,0 @@ -Reader Writer Locks pseudocode -============================== - - pthread_rwlock_rdlock(pthread_rwlock_t *rwlock); - pthread_rwlock_unlock(pthread_rwlock_t *rwlock); - pthread_rwlock_wrlock(pthread_rwlock_t *rwlock); - -struct pthread_rwlock_t { - - unsigned int lock: - - internal mutex - - unsigned int writers_preferred; - - locking mode: 0 recursive, readers preferred - 1 nonrecursive, writers preferred - - unsigned int readers; - - number of read-only references various threads have - - pthread_t writer; - - descriptor of the writer or 0 - - unsigned int readers_wakeup; - - 'all readers should wake up' futex. - - unsigned int writer_wakeup; - - 'one writer should wake up' futex. - - unsigned int nr_readers_queued; - - number of readers queued up. - - unsigned int nr_writers_queued; - - number of writers queued up. -} - -pthread_rwlock_rdlock(pthread_rwlock_t *rwlock) -{ - lll_lock(rwlock->lock); - for (;;) { - if (!rwlock->writer && (!rwlock->nr_writers_queued || - !rwlock->writers_preferred)) - break; - - rwlock->nr_readers_queued++; - val = rwlock->readers_wakeup; - lll_unlock(rwlock->lock); - - futex_wait(&rwlock->readers_wakeup, val) - - lll_lock(rwlock->lock); - rwlock->nr_readers_queued--; - } - rwlock->readers++; - lll_unlock(rwlock->lock); -} - -pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock) -{ - int result = EBUSY; - lll_lock(rwlock->lock); - if (!rwlock->writer && (!rwlock->nr_writers_queued || - !rwlock->writers_preferred)) - rwlock->readers++; - lll_unlock(rwlock->lock); - return result; -} - -pthread_rwlock_wrlock(pthread_rwlock_t *rwlock) -{ - lll_lock(rwlock->lock); - for (;;) { - if (!rwlock->writer && !rwlock->readers) - break; - - rwlock->nr_writers_queued++; - val = rwlock->writer_wakeup; - lll_unlock(rwlock->lock); - - futex_wait(&rwlock->writer_wakeup, val); - - lll_lock(rwlock->lock); - rwlock->nr_writers_queued--; - } - rwlock->writer = pthread_self(); - lll_unlock(rwlock->lock); -} - -pthread_rwlock_unlock(pthread_rwlock_t *rwlock) -{ - lll_lock(rwlock->lock); - - if (rwlock->writer) - rwlock->writer = 0; - else - rwlock->readers--; - - if (!rwlock->readers) { - if (rwlock->nr_writers_queued) { - ++rwlock->writer_wakeup; - lll_unlock(rwlock->lock); - futex_wake(&rwlock->writer_wakeup, 1); - return; - } else - if (rwlock->nr_readers_queued) { - ++rwlock->readers_wakeup; - lll_unlock(rwlock->lock); - futex_wake(&rwlock->readers_wakeup, MAX_INT); - return; - } - } - - lll_unlock(rwlock->lock); -} |