Revert of Revert 221427 "Add instrumentation to the MessagePumpMac family ..."

base/message_loop/message_pump.h

 // Copyright (c) 2012 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.
 
 #ifndef BASE_MESSAGE_LOOP_MESSAGE_PUMP_H_
 #define BASE_MESSAGE_LOOP_MESSAGE_PUMP_H_
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/message_loop/timer_slack.h"
 #include "base/threading/non_thread_safe.h"
 
 namespace base {
 
+class TimeDelta;
 class TimeTicks;
 
 class BASE_EXPORT MessagePump : public NonThreadSafe {
  public:
   // Please see the comments above the Run method for an illustration of how
   // these delegate methods are used.
   class BASE_EXPORT Delegate {
    public:
     virtual ~Delegate() {}
 
     // Called from within Run in response to ScheduleWork or when the message
     // pump would otherwise call DoDelayedWork.  Returns true to indicate that
     // work was done.  DoDelayedWork will still be called if DoWork returns
     // true, but DoIdleWork will not.
     virtual bool DoWork() = 0;
 
     // Called from within Run in response to ScheduleDelayedWork or when the
     // message pump would otherwise sleep waiting for more work.  Returns true
     // to indicate that delayed work was done.  DoIdleWork will not be called
     // if DoDelayedWork returns true.  Upon return |next_delayed_work_time|
     // indicates the time when DoDelayedWork should be called again.  If
     // |next_delayed_work_time| is null (per Time::is_null), then the queue of
     // future delayed work (timer events) is currently empty, and no additional
     // calls to this function need to be scheduled.
     virtual bool DoDelayedWork(TimeTicks* next_delayed_work_time) = 0;
 
     // Called from within Run just before the message pump goes to sleep.
     // Returns true to indicate that idle work was done.
     virtual bool DoIdleWork() = 0;
+
+    // Via the two required out pointers, returns the length of the Delegate's
+    // work queue and the length of time that the first item in the queue has
+    // been waiting to run. If the work queue is empty, the count and delay
+    // will both be zero.
+    // Note that this only counts the tasks in the ready-to-run queue and not
+    // the incoming queue that is used by other threads to post tasks. The
+    // latter queue requires holding a lock, which is deemed too expensive for
+    // instrumentation code. Under normal conditions, the incoming queue should
+    // be small or zero, but under heavy loads it may be much larger and
+    // |queue_count| may be up to 1/4 the size of the incoming queue.
+    virtual void GetQueueingInformation(size_t* queue_count,
+                                        TimeDelta* queueing_delay) {}
   };
 
   MessagePump();
   virtual ~MessagePump();
 
   // The Run method is called to enter the message pump's run loop.
   //
   // Within the method, the message pump is responsible for processing native
   // messages as well as for giving cycles to the delegate periodically.  The
   // message pump should take care to mix delegate callbacks with native
@@ skipping 68 matching lines @@
   // used on the thread that called Run.
   virtual void ScheduleDelayedWork(const TimeTicks& delayed_work_time) = 0;
 
   // Sets the timer slack to the specified value.
   virtual void SetTimerSlack(TimerSlack timer_slack);
 };
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_LOOP_MESSAGE_PUMP_H_