task: Fix deadlock between thread and iio_task_stop()

It is possible that iio_task_stop() will be called even before the
iio_task_run() thread enters the while() loop, where it waits for tasks;
in that case, both threads would be waiting on the condition variable
without anyone signaling it.

Address that issue by signaling the condition variable at the beginning
of the for() loop, and not at the end.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>

task.c

@@ -50,6 +50,9 @@ static int iio_task_run(void *d)
 	iio_mutex_lock(task->lock);
 
 	for (;;) {
+		/* Signal that we're idle */
+		iio_cond_signal(task->cond);
+
 		while (!task->stop && !(task->list && task->running)) {
 			iio_cond_wait(task->cond, task->lock, 0);
 
@@ -77,9 +80,7 @@ static int iio_task_run(void *d)
 		if (autoclear)
 			iio_task_token_destroy(entry);
 
-		/* Signal that we're done with the previous entry */
 		iio_mutex_lock(task->lock);
-		iio_cond_signal(task->cond);
 	}
 
 	iio_mutex_unlock(task->lock);