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Fix lwp_rwlock_unlock() to wake up all readers

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It woke up just one.  Bug couldn't bite, because the update never
sleeps, and therefore no reader gets a chance to sleep.
This commit is contained in:
Markus Armbruster 2009-04-26 19:44:34 +02:00
parent 2e4f63c270
commit 079fb286c5
1 changed files with 10 additions and 4 deletions
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14
src/lib/lwp/rwlock.c
View file

@ -109,6 +109,7 @@ void
lwp_rwlock_unlock(struct lwp_rwlock *rwlock) lwp_rwlock_unlock(struct lwp_rwlock *rwlock)
{ {
struct lwpProc *p; struct lwpProc *p;
int maxpri;
lwpStatus(LwpCurrent, "unlocking rwlock %s", rwlock->name); lwpStatus(LwpCurrent, "unlocking rwlock %s", rwlock->name);
if (CANT_HAPPEN(rwlock->count == 0)) if (CANT_HAPPEN(rwlock->count == 0))
@ -121,14 +122,19 @@ lwp_rwlock_unlock(struct lwp_rwlock *rwlock)
if (rwlock->count == 0 && rwlock->wq.head) { if (rwlock->count == 0 && rwlock->wq.head) {
p = lwpGetFirst(&rwlock->wq); p = lwpGetFirst(&rwlock->wq);
lwpStatus(p, "wake up next writer of rwlock %s", rwlock->name); lwpStatus(p, "wake up next writer of rwlock %s", rwlock->name);
maxpri = p->pri;
lwpReady(p);
} else if (rwlock->count >= 0 && rwlock->rq.head && !rwlock->wq.head) { } else if (rwlock->count >= 0 && rwlock->rq.head && !rwlock->wq.head) {
p = lwpGetFirst(&rwlock->rq); maxpri = 0;
lwpStatus(p, "wake up next reader of rwlock %s", rwlock->name); while ((p = lwpGetFirst(&rwlock->rq))) {
lwpStatus(p, "wake up next reader of rwlock %s", rwlock->name);
maxpri = MAX(maxpri, p->pri);
lwpReady(p);
}
} else } else
return; return;
lwpReady(p); if (LwpCurrent->pri < maxpri) {
if (LwpCurrent->pri < p->pri) {
lwpStatus(LwpCurrent, "yielding to thread with higher priority"); lwpStatus(LwpCurrent, "yielding to thread with higher priority");
lwpYield(); lwpYield();
} }