Track thread activities in order to diagnose hangs.

base/synchronization/waitable_event_win.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/synchronization/waitable_event.h"
 
 #include <windows.h>
 #include <stddef.h>
 
 #include <utility>
 
+#include "base/debug/activity_tracker.h"
 #include "base/logging.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/time/time.h"
 
 namespace base {
 
 WaitableEvent::WaitableEvent(ResetPolicy reset_policy,
                              InitialState initial_state)
     : handle_(CreateEvent(nullptr,
@@ skipping 18 matching lines @@
 
 void WaitableEvent::Signal() {
   SetEvent(handle_.Get());
 }
 
 bool WaitableEvent::IsSignaled() {
   return TimedWait(TimeDelta());
 }
 
 void WaitableEvent::Wait() {
+  // Record the event that this thread is blocking upon (for hang diagonsis).

[manzagop (departed), 2016/06/16 15:19:41]

typo: diagonsis, here an below.

+  base::debug::ScopedEventWaitActivity event_activity(this);
+
   base::ThreadRestrictions::AssertWaitAllowed();
   DWORD result = WaitForSingleObject(handle_.Get(), INFINITE);
   // It is most unexpected that this should ever fail.  Help consumers learn
   // about it if it should ever fail.
   DCHECK_EQ(WAIT_OBJECT_0, result) << "WaitForSingleObject failed";
 }
 
 bool WaitableEvent::TimedWait(const TimeDelta& max_time) {
+  // Record the event that this thread is blocking upon (for hang diagonsis).
+  base::debug::ScopedEventWaitActivity event_activity(this);
+
   base::ThreadRestrictions::AssertWaitAllowed();
   DCHECK_GE(max_time, TimeDelta());
   // Truncate the timeout to milliseconds. The API specifies that this method
   // can return in less than |max_time| (when returning false), as the argument
   // is the maximum time that a caller is willing to wait.
   DWORD timeout = saturated_cast<DWORD>(max_time.InMilliseconds());
 
   DWORD result = WaitForSingleObject(handle_.Get(), timeout);
   switch (result) {
     case WAIT_OBJECT_0:
       return true;
     case WAIT_TIMEOUT:
       return false;
   }
   // It is most unexpected that this should ever fail.  Help consumers learn
   // about it if it should ever fail.
   NOTREACHED() << "WaitForSingleObject failed";
   return false;
 }
 
 // static
 size_t WaitableEvent::WaitMany(WaitableEvent** events, size_t count) {
+  // Record the event that this thread is blocking upon (for hang diagonsis).

[manzagop (departed), 2016/06/16 15:19:41]

Put a note that this is looking at the first event?

[bcwhite, 2016/06/16 17:04:43]

Done.

+  base::debug::ScopedEventWaitActivity event_activity(events[0]);

[manzagop (departed), 2016/06/16 15:19:41]

Can count be 0?

[bcwhite, 2016/06/16 17:04:43]

Done.

+
   base::ThreadRestrictions::AssertWaitAllowed();
   HANDLE handles[MAXIMUM_WAIT_OBJECTS];
   CHECK_LE(count, static_cast<size_t>(MAXIMUM_WAIT_OBJECTS))
       << "Can only wait on " << MAXIMUM_WAIT_OBJECTS << " with WaitMany";
 
   for (size_t i = 0; i < count; ++i)
     handles[i] = events[i]->handle();
 
   // The cast is safe because count is small - see the CHECK above.
   DWORD result =
       WaitForMultipleObjects(static_cast<DWORD>(count),
                              handles,
                              FALSE,      // don't wait for all the objects
                              INFINITE);  // no timeout
   if (result >= WAIT_OBJECT_0 + count) {
     DPLOG(FATAL) << "WaitForMultipleObjects failed";
     return 0;
   }
 
   return result - WAIT_OBJECT_0;
 }
 
 }  // namespace base