compositor: add weston_client_start()

weston_client_start() is a new wrapper around weston_client_launch(),
that does the process tracking on its own, and logs the process exit
status.

When users of weston_client_start() want to know when the process exits,
they should hook into the wl_client destroy signal. This works for cases
where the client is not expected to disconnect without exiting.

As wl_client destructor and the sigchld handler run in arbitary order,
it is usually difficult for users to maintain both struct weston_process
and a struct wl_client pointer. You would need to wait for both
destructor and handler to have run, before attempting to respawn the
client.

This new function relieves the caller from the burden of maintaining the
struct weston_process, assuming the caller is only interested in client
disconnects.

Cc: Boyan Ding <stu_dby@126.com>
Cc: Derek Foreman <derekf@osg.samsung.com>
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>

src/compositor.c

@@ -319,6 +319,66 @@ weston_client_launch(struct weston_compositor *compositor,
 	return client;
 }
 
+struct process_info {
+	struct weston_process proc;
+	char *path;
+};
+
+static void
+process_handle_sigchld(struct weston_process *process, int status)
+{
+	struct process_info *pinfo =
+		container_of(process, struct process_info, proc);
+
+	/*
+	 * There are no guarantees whether this runs before or after
+	 * the wl_client destructor.
+	 */
+
+	if (WIFEXITED(status)) {
+		weston_log("%s exited with status %d\n", pinfo->path,
+			   WEXITSTATUS(status));
+	} else if (WIFSIGNALED(status)) {
+		weston_log("%s died on signal %d\n", pinfo->path,
+			   WTERMSIG(status));
+	} else {
+		weston_log("%s disappeared\n", pinfo->path);
+	}
+
+	free(pinfo->path);
+	free(pinfo);
+}
+
+WL_EXPORT struct wl_client *
+weston_client_start(struct weston_compositor *compositor, const char *path)
+{
+	struct process_info *pinfo;
+	struct wl_client *client;
+
+	pinfo = zalloc(sizeof *pinfo);
+	if (!pinfo)
+		return NULL;
+
+	pinfo->path = strdup(path);
+	if (!pinfo->path)
+		goto out_free;
+
+	client = weston_client_launch(compositor, &pinfo->proc, path,
+				      process_handle_sigchld);
+	if (!client)
+		goto out_str;
+
+	return client;
+
+out_str:
+	free(pinfo->path);
+
+out_free:
+	free(pinfo);
+
+	return NULL;
+}
+
 static void
 region_init_infinite(pixman_region32_t *region)
 {

src/compositor.h

@@ -1345,6 +1345,9 @@ weston_client_launch(struct weston_compositor *compositor,
 		     const char *path,
 		     weston_process_cleanup_func_t cleanup);
 
+struct wl_client *
+weston_client_start(struct weston_compositor *compositor, const char *path);
+
 void
 weston_watch_process(struct weston_process *process);