Fix: Synchronization issue for data available command

[lttng-tools.git] / src / common / consumer.c

diff --git a/src/common/consumer.c b/src/common/consumer.c
index d245ed7eecb385cb72b76841a14944810f9a72c1..efd9e7eb3d368552685c3e0a7bd3f54362943318 100644 (file)
--- a/src/common/consumer.c
+++ b/src/common/consumer.c
@@ -2671,6 +2671,34 @@ error:
        return ret;
 }
 
+/*
+ * Try to lock the stream mutex.
+ *
+ * On success, 1 is returned else 0 indicating that the mutex is NOT lock.
+ */
+static int stream_try_lock(struct lttng_consumer_stream *stream)
+{
+       int ret;
+
+       assert(stream);
+
+       /*
+        * Try to lock the stream mutex. On failure, we know that the stream is
+        * being used else where hence there is data still being extracted.
+        */
+       ret = pthread_mutex_trylock(&stream->lock);
+       if (ret) {
+               /* For both EBUSY and EINVAL error, the mutex is NOT locked. */
+               ret = 0;
+               goto end;
+       }
+
+       ret = 1;
+
+end:
+       return ret;
+}
+
 /*
  * Check if for a given session id there is still data needed to be extract
  * from the buffers.
@@ -2711,17 +2739,42 @@ int consumer_data_available(uint64_t id)
                        ht->hash_fct((void *)((unsigned long) id), 0x42UL),
                        ht->match_fct, (void *)((unsigned long) id),
                        &iter.iter, stream, node_session_id.node) {
-               /* Check the stream for data. */
-               ret = data_available(stream);
-               if (ret == 0) {
+               /* If this call fails, the stream is being used hence data pending. */
+               ret = stream_try_lock(stream);
+               if (!ret) {
                        goto data_not_available;
                }
 
+               /*
+                * A removed node from the hash table indicates that the stream has
+                * been deleted thus having a guarantee that the buffers are closed
+                * on the consumer side. However, data can still be transmitted
+                * over the network so don't skip the relayd check.
+                */
+               ret = cds_lfht_is_node_deleted(&stream->node.node);
+               if (!ret) {
+                       /* Check the stream if there is data in the buffers. */
+                       ret = data_available(stream);
+                       if (ret == 0) {
+                               pthread_mutex_unlock(&stream->lock);
+                               goto data_not_available;
+                       }
+               }
+
+               /* Relayd check */
                if (stream->net_seq_idx != -1) {
                        relayd = consumer_find_relayd(stream->net_seq_idx);
-                       assert(relayd);
+                       if (!relayd) {
+                               /*
+                                * At this point, if the relayd object is not available for the
+                                * given stream, it is because the relayd is being cleaned up
+                                * so every stream associated with it (for a session id value)
+                                * are or will be marked for deletion hence no data pending.
+                                */
+                               pthread_mutex_unlock(&stream->lock);
+                               goto data_not_available;
+                       }
 
-                       pthread_mutex_lock(&stream->lock);
                        pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                        if (stream->metadata_flag) {
                                ret = relayd_quiescent_control(&relayd->control_sock);
@@ -2730,11 +2783,12 @@ int consumer_data_available(uint64_t id)
                                                stream->relayd_stream_id, stream->next_net_seq_num);
                        }
                        pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
-                       pthread_mutex_unlock(&stream->lock);
                        if (ret == 0) {
+                               pthread_mutex_unlock(&stream->lock);
                                goto data_not_available;
                        }
                }
+               pthread_mutex_unlock(&stream->lock);
        }
 
        /*