diff options
Diffstat (limited to 'nptl/pthread_rwlock_tryrdlock.c')
| -rw-r--r-- | nptl/pthread_rwlock_tryrdlock.c | 25 |
1 files changed, 16 insertions, 9 deletions
diff --git a/nptl/pthread_rwlock_tryrdlock.c b/nptl/pthread_rwlock_tryrdlock.c index 368862ff07..2f94f17f36 100644 --- a/nptl/pthread_rwlock_tryrdlock.c +++ b/nptl/pthread_rwlock_tryrdlock.c @@ -94,15 +94,22 @@ __pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock) /* Same as in __pthread_rwlock_rdlock_full: We started the read phase, so we are also responsible for updating the write-phase futex. Relaxed MO is sufficient. - Note that there can be no other reader that we have to wake - because all other readers will see the read phase started by us - (or they will try to start it themselves); if a writer started - the read phase, we cannot have started it. Furthermore, we - cannot discard a PTHREAD_RWLOCK_FUTEX_USED flag because we will - overwrite the value set by the most recent writer (or the readers - before it in case of explicit hand-over) and we know that there - are no waiting readers. */ - atomic_store_relaxed (&rwlock->__data.__wrphase_futex, 0); + We have to do the same steps as a writer would when handing over the + read phase to use because other readers cannot distinguish between + us and the writer. + Note that __pthread_rwlock_tryrdlock callers will not have to be + woken up because they will either see the read phase started by us + or they will try to start it themselves; however, callers of + __pthread_rwlock_rdlock_full just increase the reader count and then + check what state the lock is in, so they cannot distinguish between + us and a writer that acquired and released the lock in the + meantime. */ + if ((atomic_exchange_relaxed (&rwlock->__data.__wrphase_futex, 0) + & PTHREAD_RWLOCK_FUTEX_USED) != 0) + { + int private = __pthread_rwlock_get_private (rwlock); + futex_wake (&rwlock->__data.__wrphase_futex, INT_MAX, private); + } } return 0; |