commit b80ef1a1d6e38f6e9b213c38b08286e5174fef23
author darin@chromium.org <darin@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98> Thu Sep 03 05:05:21 2009 +0900
committer Qijiang Fan <fqj@google.com> Thu Jun 04 09:51:11 2020 +0900
tree 6245e1082e4daddbaa3476dbb8d9130e434a3b5b
parent 36fe2217d804e20d0f4001786faa34fcc432097e

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

This is an alternative to the fix proposed here:
http://codereview.chromium.org/172101

Credit goes to Dean McNamee for discovering this performance issue!

R=deanm
BUG=20204
TEST=none

Review URL: http://codereview.chromium.org/190006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@25223 0039d316-1c4b-4281-b951-d872f2087c98


CrOS-Libchrome-Original-Commit: b2f0ea1a109f6406d6633f51adb4621090b9032d

base/message_loop.cc

diff --git a/base/message_loop.cc b/base/message_loop.cc
index 5464670..bf5256a 100644
--- a/base/message_loop.cc
+++ b/base/message_loop.cc
@@ -354,7 +354,7 @@
     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());
   }
 }

base/message_loop.h

diff --git a/base/message_loop.h b/base/message_loop.h
index 395ce6e..d2fcc12 100644
--- a/base/message_loop.h
+++ b/base/message_loop.h
@@ -281,7 +281,13 @@
     bool operator<(const PendingTask& other) const;
   };
 
-  typedef std::queue<PendingTask> TaskQueue;
+  class TaskQueue : public std::queue<PendingTask> {
+   public:
+    void Swap(TaskQueue* queue) {
+      c.swap(queue->c);  // Calls std::deque::swap
+    }
+  };
+
   typedef std::priority_queue<PendingTask> DelayedTaskQueue;
 
 #if defined(OS_WIN)