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authorUlrich Drepper <drepper@redhat.com>2000-01-05 02:09:12 +0000
committerUlrich Drepper <drepper@redhat.com>2000-01-05 02:09:12 +0000
commit1d2fc9b3c59d0e83e04139ddf633731264b76ea2 (patch)
treec738cf2a40851dc25be2c252ba5dbb7f335b5e14 /linuxthreads/spinlock.c
parentf19f2b34439145daf300bf12789bbc61c8d4db28 (diff)
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Redesigned how cancellation unblocks a thread from internal cancellation points (sem_wait, pthread_join, pthread_cond_{wait,timedwait}). Cancellation won't eat a signal in any of these functions (*required* by POSIX and Single Unix Spec!).
2000-01-03 Kaz Kylheku <kaz@ashi.footprints.net> Redesigned how cancellation unblocks a thread from internal cancellation points (sem_wait, pthread_join, pthread_cond_{wait,timedwait}). Cancellation won't eat a signal in any of these functions (*required* by POSIX and Single Unix Spec!). * condvar.c: spontaneous wakeup on pthread_cond_timedwait won't eat a simultaneous condition variable signal (not required by POSIX or Single Unix Spec, but nice). * spinlock.c: __pthread_lock queues back any received restarts that don't belong to it instead of assuming ownership of lock upon any restart; fastlock can no longer be acquired by two threads simultaneously. * restart.h: restarts queue even on kernels that don't have queued real time signals (2.0, early 2.1), thanks to atomic counter, avoiding a rare race condition in pthread_cond_timedwait.
Diffstat (limited to 'linuxthreads/spinlock.c')
-rw-r--r--linuxthreads/spinlock.c24
1 files changed, 23 insertions, 1 deletions
diff --git a/linuxthreads/spinlock.c b/linuxthreads/spinlock.c
index ce6ff9e310..b1a99d9753 100644
--- a/linuxthreads/spinlock.c
+++ b/linuxthreads/spinlock.c
@@ -40,6 +40,7 @@ void internal_function __pthread_lock(struct _pthread_fastlock * lock,
pthread_descr self)
{
long oldstatus, newstatus;
+ int spurious_wakeup_count = 0;
do {
oldstatus = lock->__status;
@@ -56,7 +57,28 @@ void internal_function __pthread_lock(struct _pthread_fastlock * lock,
}
} while(! compare_and_swap(&lock->__status, oldstatus, newstatus,
&lock->__spinlock));
- if (oldstatus != 0) suspend(self);
+
+ /* Suspend with guard against spurious wakeup.
+ This can happen in pthread_cond_timedwait_relative, when the thread
+ wakes up due to timeout and is still on the condvar queue, and then
+ locks the queue to remove itself. At that point it may still be on the
+ queue, and may be resumed by a condition signal. */
+
+ if (oldstatus != 0) {
+ for (;;) {
+ suspend(self);
+ if (self->p_nextlock != NULL) {
+ /* Count resumes that don't belong to us. */
+ spurious_wakeup_count++;
+ continue;
+ }
+ break;
+ }
+ }
+
+ /* Put back any resumes we caught that don't belong to us. */
+ while (spurious_wakeup_count--)
+ restart(self);
}
void internal_function __pthread_unlock(struct _pthread_fastlock * lock)