Revert "Avoid spurious descheduling when posting message loop tasks. (#3812)" (#3862)

This reverts commit 2062ca1.

Author: rmacnak-google

fml/message_loop_impl.cc

@@ -111,33 +111,19 @@ void MessageLoopImpl::RegisterTask(ftl::Closure task,
     // |task| synchronously within this function.
     return;
   }
-
-  ftl::TimePoint previous_wakeup, new_wakeup;
-  {
-    ftl::MutexLocker lock(&delayed_tasks_mutex_);
-    if (delayed_tasks_.empty()) {
-      previous_wakeup = ftl::TimePoint::Max();
-    } else {
-      previous_wakeup = delayed_tasks_.top().target_time;
-    }
-    delayed_tasks_.push({++order_, std::move(task), target_time});
-    new_wakeup = delayed_tasks_.top().target_time;
-  }
-  if (new_wakeup < previous_wakeup) {
-    WakeUp(new_wakeup);
-  }
+  ftl::MutexLocker lock(&delayed_tasks_mutex_);
+  delayed_tasks_.push({++order_, std::move(task), target_time});
+  WakeUp(delayed_tasks_.top().target_time);
 }
 
 void MessageLoopImpl::RunExpiredTasks() {
   TRACE_EVENT0("fml", "MessageLoop::RunExpiredTasks");
   std::vector<ftl::Closure> invocations;
 
-  ftl::TimePoint new_wakeup;
   {
     ftl::MutexLocker lock(&delayed_tasks_mutex_);
 
     if (delayed_tasks_.empty()) {
-      FTL_DCHECK(terminated_);  // No spurious wakeups except shutdown.
       return;
     }
 
@@ -151,13 +137,9 @@ void MessageLoopImpl::RunExpiredTasks() {
       delayed_tasks_.pop();
     }
 
-    if (delayed_tasks_.empty()) {
-      new_wakeup = ftl::TimePoint::Max();
-    } else {
-      new_wakeup = delayed_tasks_.top().target_time;
-    }
+    WakeUp(delayed_tasks_.empty() ? ftl::TimePoint::Max()
+                                  : delayed_tasks_.top().target_time);
   }
-  WakeUp(new_wakeup);
 
   for (const auto& invocation : invocations) {
     invocation();

fml/message_loop_unittests.cc

@@ -140,34 +140,6 @@ TEST(MessageLoop, CheckRunsTaskOnCurrentThread) {
   thread.join();
 }
 
-TEST(MessageLoop, TIME_SENSITIVE(NewTaskDueBeforePendingTask)) {
-  intptr_t tasks_run = 0;
-  std::thread thread([&tasks_run]() {
-    fml::MessageLoop::EnsureInitializedForCurrentThread();
-    auto& loop = fml::MessageLoop::GetCurrent();
-    auto begin = ftl::TimePoint::Now();
-    loop.GetTaskRunner()->PostDelayedTask(
-        [&tasks_run]() {
-          ASSERT_EQ(tasks_run, 1);
-          tasks_run++;
-          fml::MessageLoop::GetCurrent().Terminate();
-        },
-        ftl::TimeDelta::FromMilliseconds(15));
-    loop.GetTaskRunner()->PostDelayedTask(
-        [begin, &tasks_run]() {
-          ASSERT_EQ(tasks_run, 0);
-          tasks_run++;
-          auto delta = ftl::TimePoint::Now() - begin;
-          auto ms = delta.ToMillisecondsF();
-          ASSERT_LE(ms, 15);  // Did not wait for previous wakeup time.
-        },
-        ftl::TimeDelta::FromMilliseconds(5));
-    loop.Run();
-  });
-  thread.join();
-  ASSERT_EQ(tasks_run, 2);
-}
-
 TEST(MessageLoop, TIME_SENSITIVE(SingleDelayedTaskByDelta)) {
   bool checked = false;
   std::thread thread([&checked]() {

testing/run_tests.sh

@@ -3,7 +3,6 @@
 set -ex
 
 out/host_debug_unopt/ftl_unittests
-out/host_debug_unopt/fml_unittests
 out/host_debug_unopt/synchronization_unittests
 out/host_debug_unopt/wtf_unittests