+static void *call_rcu_thread(void *arg)
+{
+ [...]
+ else {
+ call_rcu_lock(&crdp->mtx);
+ crdp->flags &= ~URCU_CALL_RCU_RUNNING;
+ if (&cbs->next != cbs_tail&&
+ pthread_cond_wait(&crdp->cond,&crdp->mtx) != 0) {
+ perror("pthread_cond_wait");
+ exit(-1);
+ } else
+ poll(NULL, 0, 10);
+ crdp->flags |= URCU_CALL_RCU_RUNNING;
+ call_rcu_unlock(&crdp->mtx);
+ }
+ }
+ return NULL; /* NOTREACHED */
+}
Given the way you handle URCU_CALL_RCU_RUNNING above, the flag will be
reset in call_rcu iff call_rcu sees contention on the lock.
+ call_rcu_lock(&crdp->mtx);
+ if (!(crdp->flags& URCU_CALL_RCU_RUNNING)) {
+ if (pthread_cond_signal(&crdp->cond) != 0) {
+ perror("pthread_cond_signal");
+ exit(-1);
+ }
+ }
+ call_rcu_unlock(&crdp->mtx);
+ }
+}
So, the mutex is basically unnecessary if some futex magic replaces the
condition variable. For example, in the thread:
else {
retry:
flags = crdp->flags;
if ((flags & URCU_CALL_RCU_REQUESTED))
continue;
if (cmpxchg (&crdp->flags, flags,
flags & ~URCU_CALL_RCU_RUNNING) != flags)
goto retry;
futex_wait (&crdp->flags,
flags & ~URCU_CALL_RCU_RUNNING);
}
and in call_rcu:
mb ();
/* If the thread is not blocked, it will see our request. */
do {
flags = crdp->flags;
/* If there's already a request pending, no need to
wake up the process. If the thread is running, no
need to do anything, it'll pick up our request. */
if (flags &
(URCU_CALL_RCU_REQUESTED | URCU_CALL_RCU_RUNNING))
return;
} while (cmpxchg (&crdp->flags, flags,
flags | URCU_CALL_RCU_REQUESTED) != flags);
futex_wake (&crdp->flags, 1);
Paolo
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