X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=src%2Fcommon%2Fust-consumer%2Fust-consumer.c;h=2b55fd4637ead2b056fcafecc47ef5504d7c5df5;hb=5c827ce0dce140b121032837510f89cb70d1650d;hp=8dec2d78366af35793e56797c0db537fcfd6bc6a;hpb=a186a15913c34e8adc83ea71565d3b0eec296774;p=lttng-tools.git

diff --git a/src/common/ust-consumer/ust-consumer.c b/src/common/ust-consumer/ust-consumer.c
index 8dec2d783..2b55fd463 100644
--- a/src/common/ust-consumer/ust-consumer.c
+++ b/src/common/ust-consumer/ust-consumer.c
@@ -2,19 +2,18 @@
  * Copyright (C) 2011 - Julien Desfossez <julien.desfossez@polymtl.ca>
  *                      Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; only version 2
- * of the License.
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2 only,
+ * as published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
 #define _GNU_SOURCE
@@ -258,11 +257,20 @@ int lttng_ustconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
 		break;
 	}
 end:
-	/* signal the poll thread */
-	ret = write(ctx->consumer_poll_pipe[1], "4", 1);
-	if (ret < 0) {
-		PERROR("write consumer poll");
-	}
+	/*
+	 * Wake-up the other end by writing a null byte in the pipe
+	 * (non-blocking). Important note: Because writing into the
+	 * pipe is non-blocking (and therefore we allow dropping wakeup
+	 * data, as long as there is wakeup data present in the pipe
+	 * buffer to wake up the other end), the other end should
+	 * perform the following sequence for waiting:
+	 * 1) empty the pipe (reads).
+	 * 2) perform update operation.
+	 * 3) wait on the pipe (poll).
+	 */
+	do {
+		ret = write(ctx->consumer_poll_pipe[1], "", 1);
+	} while (ret == -1UL && errno == EINTR);
 end_nosignal:
 	return 0;
 }