From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 24 Aug 2011 20:21:52 +0000 (-0400)
Subject: Document prod/consumer synchro
X-Git-Tag: v1.9.1~261
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=49deb55988d873a8b8084ca75644b7d61c7a047c;p=lttng-ust.git

Document prod/consumer synchro

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/libringbuffer/frontend_internal.h b/libringbuffer/frontend_internal.h
index 02cb4d4a..1fb08dfd 100644
--- a/libringbuffer/frontend_internal.h
+++ b/libringbuffer/frontend_internal.h
@@ -386,6 +386,20 @@ void lib_ring_buffer_check_deliver(const struct lib_ring_buffer_config *config,
 					 * 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
+					 * consumer), the consumer
+					 * should perform the following
+					 * sequence for waiting:
+					 * 1) empty the pipe (reads).
+					 * 2) check if there is data in
+					 *    the buffer.
+					 * 3) wait on the pipe (poll).
 					 */
 					do {
 						ret = write(wakeup_fd, "", 1);