From 9c9d917cfe2e6a9f35ef82cb64e442451210716f Mon Sep 17 00:00:00 2001
From: =?utf8?q?J=C3=A9r=C3=A9mie=20Galarneau?=
 <jeremie.galarneau@efficios.com>
Date: Thu, 6 Dec 2018 12:03:48 -0500
Subject: [PATCH] Make the launch of the application registration thread
 blocking
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
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Waiting for the application registration thread to be ready to
accept application connection ensures that the application
registration socket is created and being listened-to before the parent
is signalled.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---
 src/bin/lttng-sessiond/register.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/bin/lttng-sessiond/register.c b/src/bin/lttng-sessiond/register.c
index 6776019c6..319514a36 100644
--- a/src/bin/lttng-sessiond/register.c
+++ b/src/bin/lttng-sessiond/register.c
@@ -37,6 +37,7 @@
 struct thread_notifiers {
 	struct lttng_pipe *quit_pipe;
 	struct ust_cmd_queue *ust_cmd_queue;
+	sem_t ready;
 };
 
 /*
@@ -113,6 +114,21 @@ static void cleanup_application_registration_thread(void *data)
 	free(notifiers);
 }
 
+static
+void mark_thread_as_ready(struct thread_notifiers *notifiers)
+{
+	DBG("Marking application registration thread as ready");
+	sem_post(&notifiers->ready);
+}
+
+static
+void wait_until_thread_is_ready(struct thread_notifiers *notifiers)
+{
+	DBG("Waiting for application registration thread to be ready");
+	sem_wait(&notifiers->ready);
+	DBG("Application registration thread is ready");
+}
+
 /*
  * This thread manage application registration.
  */
@@ -150,6 +166,8 @@ static void *thread_application_registration(void *data)
 		goto error_listen;
 	}
 
+	mark_thread_as_ready(notifiers);
+
 	/*
 	 * Pass 2 as size here for the thread quit pipe and apps_sock. Nothing
 	 * more will be added to this poll set.
@@ -379,6 +397,7 @@ struct lttng_thread *launch_application_registration_thread(
 	}
 	notifiers->quit_pipe = quit_pipe;
 	notifiers->ust_cmd_queue = cmd_queue;
+	sem_init(&notifiers->ready, 0, 0);
 
 	thread = lttng_thread_create("UST application registration",
 			thread_application_registration,
@@ -388,6 +407,7 @@ struct lttng_thread *launch_application_registration_thread(
 	if (!thread) {
 		goto error;
 	}
+	wait_until_thread_is_ready(notifiers);
 	return thread;
 error:
 	cleanup_application_registration_thread(notifiers);
-- 
2.34.1