Track thread activities in order to diagnose hangs.

base/synchronization/waitable_event_posix.cc

Index: base/synchronization/waitable_event_posix.cc
diff --git a/base/synchronization/waitable_event_posix.cc b/base/synchronization/waitable_event_posix.cc
index b32c882711638f497c7e260398c7eca265202565..7242e1609472b74328106a995a02e84d3448ca4c 100644
--- a/base/synchronization/waitable_event_posix.cc
+++ b/base/synchronization/waitable_event_posix.cc
@@ -7,6 +7,7 @@
 #include <algorithm>
 #include <vector>
 
+#include "base/debug/activity_tracker.h"
 #include "base/logging.h"
 #include "base/synchronization/condition_variable.h"
 #include "base/synchronization/lock.h"
@@ -157,6 +158,9 @@ void WaitableEvent::Wait() {
 }
 
 bool WaitableEvent::TimedWait(const TimeDelta& max_time) {
+  // Record the event that this thread is blocking upon (for hang diagonsis).

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

typo: disgonsis, here and below.

+  base::debug::ScopedEventWaitActivity event_activity(this);
+
   base::ThreadRestrictions::AssertWaitAllowed();
   const TimeTicks end_time(TimeTicks::Now() + max_time);
   const bool finite_time = max_time.ToInternalValue() >= 0;
@@ -229,6 +233,10 @@ cmp_fst_addr(const std::pair<WaitableEvent*, unsigned> &a,
 // static
 size_t WaitableEvent::WaitMany(WaitableEvent** raw_waitables,
                                size_t count) {
+  // Record the event that this thread is blocking upon (for hang diagonsis).

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

Can |count| be 0?

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

Make note only considering first event?

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

There's a DCHECK(count) below, so no.  But I should probably move this var to
below that.

+  // Extra parenthesis needed so C++ doesn't think this is a function prototype.

[manzagop (departed), 2016/06/16 15:19:40]

Dead comment?

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

Done.

+  base::debug::ScopedEventWaitActivity event_activity(raw_waitables[0]);
+
   base::ThreadRestrictions::AssertWaitAllowed();
   DCHECK(count) << "Cannot wait on no events";