Commit 77ddcd5a authored Mar 23, 2017 by Tom Cherry

init: Prevent spin loop while waiting for exec or property

Currently, when we are waiting for an exec service or a property, if
there are either any services to be restarted or any more commands to
be run, we set the epoll_timeout to handle these events.  However, we
don't actually restart and processes or execute any commands while
waiting, so this essentially turns this waiting into a spin loop,
particularly in the common case of having more commands to execute,
where epoll_timeout is set to 0.

The change only sets epoll_timeout if we're not waiting.

Note that the only way to stop waiting for an exec service or a
property is for a signal or property to be delivered to init, which
happens through the epoll fds, so it's safe to indefinitely wait for
epoll to return.

Test: Boot bullhead
Change-Id: Iae3b217eb28182038b464fd39df8e7d27b5e23ff

parent 2af784bf

init/init.cpp

+12 −10

Original line number	Diff line number	Diff line
		@@ -1322,13 +1322,14 @@ int main(int argc, char** argv) {
		am.QueueBuiltinAction(queue_property_triggers_action, "queue_property_triggers");

		while (true) {
		// By default, sleep until something happens.
		int epoll_timeout_ms = -1;

		if (!(waiting_for_exec \|\| waiting_for_prop)) {
		am.ExecuteOneCommand();
		restart_processes();
		}

		// By default, sleep until something happens.
		int epoll_timeout_ms = -1;
		if (!(waiting_for_exec \|\| waiting_for_prop)) {
		restart_processes();

		// If there's a process that needs restarting, wake up in time for that.
		if (process_needs_restart_at != 0) {
		@@ -1338,6 +1339,7 @@ int main(int argc, char** argv) {

		// If there's more work to do, wake up again immediately.
		if (am.HasMoreCommands()) epoll_timeout_ms = 0;
		}

		epoll_event ev;
		int nr = TEMP_FAILURE_RETRY(epoll_wait(epoll_fd, &ev, 1, epoll_timeout_ms));