ao_write: Check return value of pthread functions.

Although pthread_cond_wait() and pthread_cond_signal() should never
fail on our setup, let's be conservative here and check the return
value anyway.

This patch also adds some comments and removes a few lines of code
which were commented out since day one of the ao writer.

diff --git a/ao_write.c b/ao_write.c
index 12ab77fe8dc33c1b5be189eff6bd4621cb4305a6..d1d62a6d9d3c3f0f0acdf25ccfa8d7224b8f2eeb 100644 (file)
--- a/ao_write.c
+++ b/ao_write.c
@@ -28,6 +28,7 @@ struct private_aow_data {
 
        pthread_t thread;
        pthread_attr_t attr;
+       /* The mutex and the condition variable serialize access to ->btrn */
        pthread_mutex_t mutex;
        pthread_cond_t data_available;
        struct btr_node *thread_btrn;
@@ -224,10 +225,6 @@ __noreturn static void *aow_play(void *priv)
        int ret;
 
        for (;;) {
-               /*
-                * Lock mutex and wait for signal. pthread_cond_wait() will
-                * automatically and atomically unlock mutex while it waits.
-                */
                pthread_mutex_lock(&pawd->mutex);
                for (;;) {
                        ret = btr_node_status(btrn, wn->min_iqs, BTR_NT_LEAF);
@@ -243,10 +240,16 @@ __noreturn static void *aow_play(void *priv)
                                ret = -E_WRITE_COMMON_EOF;
                                goto unlock;
                        }
-                       //PARA_CRIT_LOG("waiting for data\n");
-                       //usleep(1000);
-                       //pthread_mutex_unlock(&pawd->mutex);
-                       pthread_cond_wait(&pawd->data_available, &pawd->mutex);
+                       /*
+                        * No data available, go to sleep and wait for the main
+                        * thread to wake us up. pthread_cond_wait() unlocks
+                        * the mutex while it waits and locks it again upon
+                        * return.
+                        */
+                       ret = pthread_cond_wait(&pawd->data_available,
+                               &pawd->mutex);
+                       /* pthread_cond_wait() can never fail here */
+                       assert(ret == 0);
                }
                pthread_mutex_unlock(&pawd->mutex);
                assert(frames > 0);
@@ -358,7 +361,11 @@ static int aow_post_select(__a_unused struct sched *s,
        ret = btr_node_status(wn->btrn, wn->min_iqs, BTR_NT_LEAF);
        if (ret > 0) {
                btr_pushdown(wn->btrn);
-               pthread_cond_signal(&pawd->data_available);
+               if (pthread_cond_signal(&pawd->data_available) != 0) {
+                       ret = -E_AO_PTHREAD;
+                       PARA_ERROR_LOG("pthread_cond_signal() failed\n");
+                       goto remove_thread_btrn;
+               }
        }
        pthread_mutex_unlock(&pawd->mutex);
        if (ret >= 0)