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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
This commit is contained in:
Tom Cherry 2017-03-23 16:54:38 -07:00
parent 2af784bf20
commit 77ddcd5a3f
1 changed files with 13 additions and 11 deletions
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24
init/init.cpp
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@ -1322,22 +1322,24 @@ int main(int argc, char** argv) {
am.QueueBuiltinAction(queue_property_triggers_action, "queue_property_triggers");
while (true) {
if (!(waiting_for_exec || waiting_for_prop)) {
am.ExecuteOneCommand();
restart_processes();
}
// By default, sleep until something happens.
int epoll_timeout_ms = -1;
// If there's a process that needs restarting, wake up in time for that.
if (process_needs_restart_at != 0) {
epoll_timeout_ms = (process_needs_restart_at - time(nullptr)) * 1000;
if (epoll_timeout_ms < 0) epoll_timeout_ms = 0;
if (!(waiting_for_exec || waiting_for_prop)) {
am.ExecuteOneCommand();
}
if (!(waiting_for_exec || waiting_for_prop)) {
restart_processes();
// If there's more work to do, wake up again immediately.
if (am.HasMoreCommands()) epoll_timeout_ms = 0;
// If there's a process that needs restarting, wake up in time for that.
if (process_needs_restart_at != 0) {
epoll_timeout_ms = (process_needs_restart_at - time(nullptr)) * 1000;
if (epoll_timeout_ms < 0) epoll_timeout_ms = 0;
}
// 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));