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Make empth_rwlock_t prefer writers

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LWP and Windows implementations already did that.  Rewrite the
pthreads implementation.

The write-bias makes the stupid play_wrlock_wanted busy wait in
dispatch() unnecessary.  Remove it.
This commit is contained in:
Markus Armbruster 2009-04-26 23:48:05 +02:00
parent 079fb286c5
commit d052239a7a
3 changed files with 47 additions and 28 deletions
Download patch file Download diff file Expand all files Collapse all files

53
src/lib/empthread/pthread.c
View file

@ -62,8 +62,12 @@ struct empth_t {
};
struct empth_rwlock_t {
/* Can't use pthread_rwlock_t, because it needn't prefer writers */
char *name;
pthread_rwlock_t lock;
int nread; /* #active readers */
int nwrite; /* total #writers (active and waiting) */
pthread_cond_t can_read;
pthread_cond_t can_write;
};
/* Thread-specific data key */
@ -397,19 +401,22 @@ empth_rwlock_create(char *name)
if (!rwlock)
return NULL;
if (pthread_rwlock_init(&rwlock->lock, NULL) != 0) {
if (pthread_cond_init(&rwlock->can_read, NULL) != 0
|| pthread_cond_init(&rwlock->can_write, NULL) != 0) {
free(rwlock);
return NULL;
}
rwlock->name = strdup(name);
rwlock->nread = rwlock->nwrite = 0;
return rwlock;
}
void
empth_rwlock_destroy(empth_rwlock_t *rwlock)
{
pthread_rwlock_destroy(&rwlock->lock);
pthread_cond_destroy(&rwlock->can_read);
pthread_cond_destroy(&rwlock->can_write);
free(rwlock->name);
free(rwlock);
}
@ -417,23 +424,45 @@ empth_rwlock_destroy(empth_rwlock_t *rwlock)
void
empth_rwlock_wrlock(empth_rwlock_t *rwlock)
{
pthread_mutex_unlock(&mtx_ctxsw);
pthread_rwlock_wrlock(&rwlock->lock);
pthread_mutex_lock(&mtx_ctxsw);
empth_restorectx();
empth_status("wrlock %s %d %d",
rwlock->name, rwlock->nread, rwlock->nwrite);
rwlock->nwrite++;
while (rwlock->nread != 0 || rwlock->nwrite != 1) {
empth_status("waiting for wrlock %s", rwlock->name);
pthread_cond_wait(&rwlock->can_write, &mtx_ctxsw);
empth_status("got wrlock %s %d %d",
rwlock->name, rwlock->nread, rwlock->nwrite);
empth_restorectx();
}
}
void
empth_rwlock_rdlock(empth_rwlock_t *rwlock)
{
pthread_mutex_unlock(&mtx_ctxsw);
pthread_rwlock_rdlock(&rwlock->lock);
pthread_mutex_lock(&mtx_ctxsw);
empth_restorectx();
empth_status("rdlock %s %d %d",
rwlock->name, rwlock->nread, rwlock->nwrite);
while (rwlock->nwrite) {
empth_status("waiting for rdlock %s", rwlock->name);
pthread_cond_wait(&rwlock->can_read, &mtx_ctxsw);
empth_status("got rdlock %s %d %d",
rwlock->name, rwlock->nread, rwlock->nwrite);
empth_restorectx();
}
rwlock->nread++;
}
void
empth_rwlock_unlock(empth_rwlock_t *rwlock)
{
pthread_rwlock_unlock(&rwlock->lock);
if (CANT_HAPPEN(!rwlock->nread && !rwlock->nwrite))
return;
if (rwlock->nread) { /* holding read lock */
if (!--rwlock->nread)
pthread_cond_signal(&rwlock->can_write);
} else {
rwlock->nwrite--;
pthread_cond_signal(&rwlock->can_write);
}
if (rwlock->nwrite == 0)
pthread_cond_broadcast(&rwlock->can_read);
}