Make swapping the incoming queue with the work queue constant time....

base/message_loop.cc

 // Copyright (c) 2009 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/message_loop.h"
 
 #include <algorithm>
 
 #include "base/compiler_specific.h"
 #include "base/lazy_instance.h"
@@ skipping 336 matching lines @@
   // load.  That reduces the number of locks-per-task significantly when our
   // queues get large.
   if (!work_queue_.empty())
     return;  // Wait till we *really* need to lock and load.
 
   // Acquire all we can from the inter-thread queue with one lock acquisition.
   {
     AutoLock lock(incoming_queue_lock_);
     if (incoming_queue_.empty())
       return;
-    std::swap(incoming_queue_, work_queue_);
+    incoming_queue_.Swap(&work_queue_);  // Constant time
     DCHECK(incoming_queue_.empty());
   }
 }
 
 bool MessageLoop::DeletePendingTasks() {
   bool did_work = !work_queue_.empty();
   while (!work_queue_.empty()) {
     PendingTask pending_task = work_queue_.front();
     work_queue_.pop();
     if (!pending_task.delayed_run_time.is_null()) {
@@ skipping 254 matching lines @@
                                            Watcher *delegate) {
   return pump_libevent()->WatchFileDescriptor(
       fd,
       persistent,
       static_cast<base::MessagePumpLibevent::Mode>(mode),
       controller,
       delegate);
 }
 
 #endif