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authorTorvald Riegel <triegel@redhat.com>2015-04-28 23:24:36 +0200
committerTorvald Riegel <triegel@redhat.com>2015-06-04 15:34:30 +0200
commitb634486d57a14b53f1cfcf739e41ddf826e51977 (patch)
tree65ad6788da14adc8effdd9d1b4236ac24af710d7 /nptl/pthread_rwlock_tryrdlock.c
parent3c9c61febede148b79d8509e16588152d99b3774 (diff)
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Fix missing wake-ups in pthread_rwlock_rdlock.
This adds wake-ups that would be missing if assuming that for a non-writer-preferring rwlock, if one thread has acquired a rdlock and does not release it, another thread will eventually acquire a rdlock too despite concurrent write lock acquisition attempts. BZ 14958 is about supporting this assumption. Strictly speaking, this isn't a valid test case, but nonetheless worth supporting (see comment 7 of BZ 14958).
Diffstat (limited to 'nptl/pthread_rwlock_tryrdlock.c')
-rw-r--r--nptl/pthread_rwlock_tryrdlock.c18
1 files changed, 17 insertions, 1 deletions
diff --git a/nptl/pthread_rwlock_tryrdlock.c b/nptl/pthread_rwlock_tryrdlock.c
index d51d9aa930..cde123fd5d 100644
--- a/nptl/pthread_rwlock_tryrdlock.c
+++ b/nptl/pthread_rwlock_tryrdlock.c
@@ -20,12 +20,14 @@
#include "pthreadP.h"
#include <lowlevellock.h>
#include <elide.h>
+#include <stdbool.h>
int
__pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
{
int result = EBUSY;
+ bool wake = false;
if (ELIDE_TRYLOCK (rwlock->__data.__rwelision,
rwlock->__data.__lock == 0
@@ -45,11 +47,25 @@ __pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
result = EAGAIN;
}
else
- result = 0;
+ {
+ result = 0;
+ /* See pthread_rwlock_rdlock. */
+ if (rwlock->__data.__nr_readers == 1
+ && rwlock->__data.__nr_readers_queued > 0
+ && rwlock->__data.__nr_writers_queued > 0)
+ {
+ ++rwlock->__data.__readers_wakeup;
+ wake = true;
+ }
+ }
}
lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
+ if (wake)
+ lll_futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX,
+ rwlock->__data.__shared);
+
return result;
}
strong_alias (__pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock)