Fix: ust-consumer: metadata thread not woken-up after version change

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

diff --git a/src/common/consumer/consumer.c b/src/common/consumer/consumer.c
index 23853e5c29378c80144cfb1bda98cd2fe83305e7..cecdc3f9152e705b0b1f426856e167959c4d0283 100644 (file)
--- a/src/common/consumer/consumer.c
+++ b/src/common/consumer/consumer.c
@@ -877,6 +877,43 @@ error:
        return outfd;
 }
 
+/*
+ * Write a character on the metadata poll pipe to wake the metadata thread.
+ * Returns 0 on success, -1 on error.
+ */
+int consumer_metadata_wakeup_pipe(const struct lttng_consumer_channel *channel)
+{
+       int ret = 0;
+
+       DBG("Waking up metadata poll thread (writing to pipe): channel name = '%s'",
+                       channel->name);
+       if (channel->monitor && channel->metadata_stream) {
+               const char dummy = 'c';
+               const ssize_t write_ret = lttng_write(
+                               channel->metadata_stream->ust_metadata_poll_pipe[1],
+                               &dummy, 1);
+
+               if (write_ret < 1) {
+                       if (errno == EWOULDBLOCK) {
+                               /*
+                                * This is fine, the metadata poll thread
+                                * is having a hard time keeping-up, but
+                                * it will eventually wake-up and consume
+                                * the available data.
+                                */
+                               ret = 0;
+                       } else {
+                               PERROR("Failed to write to UST metadata pipe while attempting to wake-up the metadata poll thread");
+                               ret = -1;
+                               goto end;
+                       }
+               }
+       }
+
+end:
+       return ret;
+}
+
 /*
  * Trigger a dump of the metadata content. Following/during the succesful
  * completion of this call, the metadata poll thread will start receiving