X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=src%2Fbin%2Flttng-sessiond%2Fmain.c;h=f7b3c7c84d1add69c1114e89f81ac4911490b33d;hb=a0e4ba18a275734e0934ba4d8d598bbcec7d52bb;hp=e727888181d8ae1089e967297adec076a6a8585e;hpb=e6c533d671c9bcde5d914a18a632b6d0782c4e1a;p=lttng-tools.git

diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
index e72788818..f7b3c7c84 100644
--- a/src/bin/lttng-sessiond/main.c
+++ b/src/bin/lttng-sessiond/main.c
@@ -286,13 +286,39 @@ struct notification_thread_handle *notification_thread_handle;
 struct lttng_ht *agent_apps_ht_by_sock = NULL;
 
 /*
- * Whether sessiond is ready for commands/notification channel/health check
+ * The initialization of the session daemon is done in multiple phases.
+ *
+ * While all threads are launched near-simultaneously, only some of them
+ * are needed to ensure the session daemon can start to respond to client
  * requests.
- * NR_LTTNG_SESSIOND_READY must match the number of calls to
- * sessiond_notify_ready().
+ *
+ * There are two important guarantees that we wish to offer with respect
+ * to the initialisation of the session daemon:
+ *   - When the daemonize/background launcher process exits, the sessiond
+ *     is fully able to respond to client requests,
+ *   - Auto-loaded sessions are visible to clients.
+ *
+ * In order to achieve this, a number of support threads have to be launched
+ * to allow the "client" thread to function properly. Moreover, since the
+ * "load session" thread needs the client thread, we must provide a way
+ * for the "load session" thread to know that the "client" thread is up
+ * and running.
+ *
+ * Hence, the support threads decrement the lttng_sessiond_ready counter
+ * while the "client" threads waits for it to reach 0. Once the "client" thread
+ * unblocks, it posts the message_thread_ready semaphore which allows the
+ * "load session" thread to progress.
+ *
+ * This implies that the "load session" thread is the last to be initialized
+ * and will explicitly call sessiond_signal_parents(), which signals the parents
+ * that the session daemon is fully initialized.
+ *
+ * The three (3) support threads are:
+ *  - agent_thread
+ *  - notification_thread
+ *  - health_thread
  */
-#define NR_LTTNG_SESSIOND_READY		5
-int lttng_sessiond_ready = NR_LTTNG_SESSIOND_READY;
+int lttng_sessiond_ready = 3;
 
 int sessiond_check_thread_quit_pipe(int fd, uint32_t events)
 {
@@ -301,28 +327,36 @@ int sessiond_check_thread_quit_pipe(int fd, uint32_t events)
 
 /* Notify parents that we are ready for cmd and health check */
 LTTNG_HIDDEN
-void sessiond_notify_ready(void)
+void sessiond_signal_parents(void)
 {
-	if (uatomic_sub_return(&lttng_sessiond_ready, 1) == 0) {
-		/*
-		 * Notify parent pid that we are ready to accept command
-		 * for client side.  This ppid is the one from the
-		 * external process that spawned us.
-		 */
-		if (config.sig_parent) {
-			kill(ppid, SIGUSR1);
-		}
+	/*
+	 * Notify parent pid that we are ready to accept command
+	 * for client side.  This ppid is the one from the
+	 * external process that spawned us.
+	 */
+	if (config.sig_parent) {
+		kill(ppid, SIGUSR1);
+	}
 
-		/*
-		 * Notify the parent of the fork() process that we are
-		 * ready.
-		 */
-		if (config.daemonize || config.background) {
-			kill(child_ppid, SIGUSR1);
-		}
+	/*
+	 * Notify the parent of the fork() process that we are
+	 * ready.
+	 */
+	if (config.daemonize || config.background) {
+		kill(child_ppid, SIGUSR1);
 	}
 }
 
+LTTNG_HIDDEN
+void sessiond_notify_ready(void)
+{
+	/*
+	 * The _return variant is used since the implied memory barriers are
+	 * required.
+	 */
+	(void) uatomic_sub_return(&lttng_sessiond_ready, 1);
+}
+
 static
 int __sessiond_set_thread_pollset(struct lttng_poll_event *events, size_t size,
 		int *a_pipe)
@@ -513,15 +547,9 @@ static void sessiond_cleanup(void)
 	 */
 	utils_close_pipe(thread_quit_pipe);
 
-	/*
-	 * If config.pid_file_path.value is undefined, the default file will be
-	 * wiped when removing the rundir.
-	 */
-	if (config.pid_file_path.value) {
-		ret = remove(config.pid_file_path.value);
-		if (ret < 0) {
-			PERROR("remove pidfile %s", config.pid_file_path.value);
-		}
+	ret = remove(config.pid_file_path.value);
+	if (ret < 0) {
+		PERROR("remove pidfile %s", config.pid_file_path.value);
 	}
 
 	DBG("Removing sessiond and consumerd content of directory %s",
@@ -4286,8 +4314,6 @@ static void *thread_manage_clients(void *data)
 		goto error;
 	}
 
-	sessiond_notify_ready();
-
 	ret = sem_post(&load_info->message_thread_ready);
 	if (ret) {
 		PERROR("sem_post message_thread_ready");
@@ -4321,6 +4347,16 @@ static void *thread_manage_clients(void *data)
 			goto exit;
 		}
 	}
+	/*
+	 * This barrier is paired with the one in sessiond_notify_ready() to
+	 * ensure that loads accessing data initialized by the other threads,
+	 * on which this thread was waiting, are not performed before this point.
+	 *
+	 * Note that this could be a 'read' memory barrier, but a full barrier
+	 * is used in case the code changes. The performance implications of
+	 * this choice are minimal since this is a slow path.
+	 */
+	cmm_smp_mb();
 
 	/* This testpoint is after we signal readiness to the parent. */
 	if (testpoint(sessiond_thread_manage_clients)) {
@@ -5510,6 +5546,12 @@ int main(int argc, char **argv)
 		goto exit_set_signal_handler;
 	}
 
+	/*
+	 * Init config from environment variables.
+	 * Command line option override env configuration per-doc. Do env first.
+	 */
+	sessiond_config_apply_env_config(&config);
+
 	/*
 	 * Parse arguments and load the daemon configuration file.
 	 *
@@ -5524,9 +5566,6 @@ int main(int argc, char **argv)
 		goto exit_options;
 	}
 
-	/* Init config from environment variables. */
-	sessiond_config_apply_env_config(&config);
-
 	/*
 	 * Resolve all paths received as arguments, configuration option, or
 	 * through environment variable as absolute paths. This is necessary