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

init/init.cpp

@@ -1322,23 +1322,25 @@ 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();
         }
+        if (!(waiting_for_exec || waiting_for_prop)) {
+            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 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;
         }
 
-        // 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));
         if (nr == -1) {