Ensure that content will consistently return the same MessageLoopProxy for a given BrowserThread

content/browser/browser_thread_impl.cc

 // 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.
 
 #include "content/browser/browser_thread_impl.h"
 
 #include <string>
 
 #include "base/atomicops.h"
 #include "base/bind.h"
@@ skipping 13 matching lines @@
 static const char* g_browser_thread_names[BrowserThread::ID_COUNT] = {
   "",  // UI (name assembled in browser_main.cc).
   "Chrome_DBThread",  // DB
   "Chrome_FileThread",  // FILE
   "Chrome_FileUserBlockingThread",  // FILE_USER_BLOCKING
   "Chrome_ProcessLauncherThread",  // PROCESS_LAUNCHER
   "Chrome_CacheThread",  // CACHE
   "Chrome_IOThread",  // IO
 };
 
+// An implementation of MessageLoopProxy to be used in conjunction
+// with BrowserThread.
+class BrowserThreadMessageLoopProxy : public base::MessageLoopProxy {
+ public:
+  explicit BrowserThreadMessageLoopProxy(BrowserThread::ID identifier)
+      : id_(identifier) {
+  }
+
+  // MessageLoopProxy implementation.
+  virtual bool PostDelayedTask(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task, base::TimeDelta delay) OVERRIDE {
+    return BrowserThread::PostDelayedTask(id_, from_here, task, delay);
+  }
+
+  virtual bool PostNonNestableDelayedTask(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task,
+      base::TimeDelta delay) OVERRIDE {
+    return BrowserThread::PostNonNestableDelayedTask(id_, from_here, task,
+                                                     delay);
+  }
+
+  virtual bool RunsTasksOnCurrentThread() const OVERRIDE {
+    return BrowserThread::CurrentlyOn(id_);
+  }
+
+ protected:
+  virtual ~BrowserThreadMessageLoopProxy() {}
+
+ private:
+  BrowserThread::ID id_;
+  DISALLOW_COPY_AND_ASSIGN(BrowserThreadMessageLoopProxy);
+};
+
+// A separate helper is used just for the proxies, in order to avoid needing
+// to initialize the globals to create a proxy.
+struct BrowserThreadProxies {
+  BrowserThreadProxies() {
+    for (int i = 0; i < BrowserThread::ID_COUNT; ++i) {
+      proxies[i] =
+          new BrowserThreadMessageLoopProxy(static_cast<BrowserThread::ID>(i));
+    }
+  }
+
+  scoped_refptr<base::MessageLoopProxy> proxies[BrowserThread::ID_COUNT];
+};
+
+base::LazyInstance<BrowserThreadProxies>::Leaky
+    g_proxies = LAZY_INSTANCE_INITIALIZER;
+
 struct BrowserThreadGlobals {
   BrowserThreadGlobals()
       : blocking_pool(new base::SequencedWorkerPool(3, "BrowserBlocking")) {
     memset(threads, 0, BrowserThread::ID_COUNT * sizeof(threads[0]));
     memset(thread_delegates, 0,
            BrowserThread::ID_COUNT * sizeof(thread_delegates[0]));
   }
 
   // This lock protects |threads|. Do not read or modify that array
   // without holding this lock. Do not block while holding this lock.
@@ skipping 223 matching lines @@
       message_loop->PostNonNestableDelayedTask(from_here, task, delay);
     }
   }
 
   if (!target_thread_outlives_current)
     globals.lock.Release();
 
   return !!message_loop;
 }
 
-// An implementation of MessageLoopProxy to be used in conjunction
-// with BrowserThread.
-class BrowserThreadMessageLoopProxy : public base::MessageLoopProxy {
- public:
-  explicit BrowserThreadMessageLoopProxy(BrowserThread::ID identifier)
-      : id_(identifier) {
-  }
-
-  // MessageLoopProxy implementation.
-  virtual bool PostDelayedTask(
-      const tracked_objects::Location& from_here,
-      const base::Closure& task, base::TimeDelta delay) OVERRIDE {
-    return BrowserThread::PostDelayedTask(id_, from_here, task, delay);
-  }
-
-  virtual bool PostNonNestableDelayedTask(
-      const tracked_objects::Location& from_here,
-      const base::Closure& task,
-      base::TimeDelta delay) OVERRIDE {
-    return BrowserThread::PostNonNestableDelayedTask(id_, from_here, task,
-                                                     delay);
-  }
-
-  virtual bool RunsTasksOnCurrentThread() const OVERRIDE {
-    return BrowserThread::CurrentlyOn(id_);
-  }
-
- protected:
-  virtual ~BrowserThreadMessageLoopProxy() {}
-
- private:
-  BrowserThread::ID id_;
-  DISALLOW_COPY_AND_ASSIGN(BrowserThreadMessageLoopProxy);
-};
-
 // static
 bool BrowserThread::PostBlockingPoolTask(
     const tracked_objects::Location& from_here,
     const base::Closure& task) {
   return g_globals.Get().blocking_pool->PostWorkerTask(from_here, task);
 }
 
 // static
 bool BrowserThread::PostBlockingPoolTaskAndReply(
     const tracked_objects::Location& from_here,
@@ skipping 148 matching lines @@
       return true;
     }
   }
 
   return false;
 }
 
 // static
 scoped_refptr<base::MessageLoopProxy>
 BrowserThread::GetMessageLoopProxyForThread(ID identifier) {
-  return make_scoped_refptr(new BrowserThreadMessageLoopProxy(identifier));
+  return g_proxies.Get().proxies[identifier];
 }
 
 // static
 base::MessageLoop* BrowserThread::UnsafeGetMessageLoopForThread(ID identifier) {
   if (g_globals == NULL)
     return NULL;
 
   BrowserThreadGlobals& globals = g_globals.Get();
   base::AutoLock lock(globals.lock);
   base::Thread* thread = globals.threads[identifier];
@@ skipping 10 matching lines @@
   AtomicWord* storage = reinterpret_cast<AtomicWord*>(
       &globals.thread_delegates[identifier]);
   AtomicWord old_pointer = base::subtle::NoBarrier_AtomicExchange(
       storage, reinterpret_cast<AtomicWord>(delegate));
 
   // This catches registration when previously registered.
   DCHECK(!delegate || !old_pointer);
 }
 
 }  // namespace content