Back out "EventBase::getRecentSteadyTime"

Summary:
Original commit changeset: 8eb472ce50bf

This breaks time measurement to include measuring the wait preceding handler/callback invocation.

Reviewed By: w-o-o

Differential Revision: D21986042

fbshipit-source-id: 42701b929878c3f56d736de5ca0417814c64fce1

folly/io/async/EventBase.cpp

@@ -215,8 +215,6 @@ EventBase::~EventBase() {
     virtualEventBaseDestroyFuture.get();
   }
 
-  bumpHandlingTime();
-
   // Call all destruction callbacks, before we start cleaning up our state.
   while (!onDestructionCallbacks_.rlock()->empty()) {
     OnDestructionCallback::List callbacks;
@@ -383,8 +381,6 @@ bool EventBase::loopBody(int flags, bool ignoreKeepAlive) {
     }
     ++nextLoopCnt_;
 
-    bumpHandlingTime();
-
     // Run the before loop callbacks
     LoopCallbackList callbacks;
     callbacks.swap(runBeforeLoopCallbacks_);
@@ -406,12 +402,11 @@ bool EventBase::loopBody(int flags, bool ignoreKeepAlive) {
     ranLoopCallbacks = runLoopCallbacks();
 
     if (enableTimeMeasurement_) {
-      assert(startWork_);
       auto now = std::chrono::steady_clock::now();
       busy = std::chrono::duration_cast<std::chrono::microseconds>(
-          now - *startWork_);
+          now - startWork_);
       idle = std::chrono::duration_cast<std::chrono::microseconds>(
-          *startWork_ - idleStart);
+          startWork_ - idleStart);
       auto loop_time = busy + idle;
 
       avgLoopTime_.addSample(loop_time, busy);
@@ -561,7 +556,7 @@ void EventBase::bumpHandlingTime() {
     startWork_ = std::chrono::steady_clock::now();
 
     VLOG(11) << "EventBase " << this << " " << __PRETTY_FUNCTION__
-             << " (loop) startWork_ " << startWork_->time_since_epoch().count();
+             << " (loop) startWork_ " << startWork_.time_since_epoch().count();
   }
 }
 
@@ -687,6 +682,7 @@ void EventBase::runImmediatelyOrRunInEventBaseThreadAndWait(Func fn) noexcept {
 }
 
 bool EventBase::runLoopCallbacks() {
+  bumpHandlingTime();
   if (!loopCallbacks_.empty()) {
     // Swap the loopCallbacks_ list with a temporary list on our stack.
     // This way we will only run callbacks scheduled at the time

folly/io/async/EventBase.h

@@ -781,12 +781,6 @@ class EventBase : public TimeoutManager,
     loopOnce();
   }
 
-  Optional<std::chrono::steady_clock::time_point> getRecentSteadyTime() const
-      noexcept {
-    dcheckIsInEventBaseThread();
-    return startWork_;
-  }
-
   // Implements the ScheduledExecutor interface
   void scheduleAt(Func&& fn, TimePoint const& timeout) override;
 
@@ -914,7 +908,7 @@ class EventBase : public TimeoutManager,
   // Wrap-around loop counter to detect beginning of each loop
   std::size_t nextLoopCnt_;
   std::size_t latestLoopCnt_;
-  Optional<std::chrono::steady_clock::time_point> startWork_;
+  std::chrono::steady_clock::time_point startWork_;
   // Prevent undefined behavior from invoking event_base_loop() reentrantly.
   // This is needed since many projects use libevent-1.4, which lacks commit
   // b557b175c00dc462c1fce25f6e7dd67121d2c001 from

folly/io/async/test/EventBaseTestLib.h

@@ -2286,27 +2286,6 @@ TYPED_TEST_P(EventBaseTest1, RunOnDestructionAddCallbackWithinCallback) {
   EXPECT_EQ(2, callbacksCalled);
 }
 
-TYPED_TEST_P(EventBaseTest1, RecentSteadyTime) {
-  using namespace std::literals::chrono_literals;
-  using tp = std::chrono::steady_clock::time_point;
-  FOLLY_SKIP_IF_NULLPTR_BACKEND(evb);
-  tp a;
-  tp b;
-  tp c;
-  evb.runInEventBaseThread([&] {
-    a = evb.getRecentSteadyTime().value();
-    /* sleep override */ std::this_thread::sleep_for(10ms);
-    b = evb.getRecentSteadyTime().value();
-  });
-  evb.loop();
-  evb.runInEventBaseThread([&] { //
-    c = evb.getRecentSteadyTime().value();
-  });
-  evb.loop();
-  EXPECT_EQ(a, b);
-  EXPECT_LT(a, c);
-}
-
 REGISTER_TYPED_TEST_CASE_P(
     EventBaseTest,
     ReadEvent,
@@ -2371,7 +2350,6 @@ REGISTER_TYPED_TEST_CASE_P(
     RunOnDestructionCancelled,
     RunOnDestructionAfterHandleDestroyed,
     RunOnDestructionAddCallbackWithinCallback,
-    InternalExternalCallbackOrderTest,
-    RecentSteadyTime);
+    InternalExternalCallbackOrderTest);
 } // namespace test
 } // namespace folly