The Tor Browser: ipc/chromium/src/base/observer_list_threadsafe.h@6474c204b198 (annotated)

ipc/chromium/src/base/observer_list_threadsafe.h@6474c204b198 (annotated)

ipc/chromium/src/base/observer_list_threadsafe.h

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 // Copyright (c) 2006-2008 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_OBSERVER_LIST_THREADSAFE_H_
 #define BASE_OBSERVER_LIST_THREADSAFE_H_
 #include <vector>
 #include <algorithm>
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
 #include "base/observer_list.h"
 #include "base/ref_counted.h"
 #include "base/task.h"
 namespace base {
 ///////////////////////////////////////////////////////////////////////////////
 //
 // OVERVIEW:
 //
 //   A thread-safe container for a list of observers.
 //   This is similar to the observer_list (see observer_list.h), but it
 //   is more robust for multi-threaded situations.
 //
 //   The following use cases are supported:
 //    * Observers can register for notifications from any thread.
 //      Callbacks to the observer will occur on the same thread where
 //      the observer initially called AddObserver() from.
 //    * Any thread may trigger a notification via NOTIFY_OBSERVERS.
 //    * Observers can remove themselves from the observer list inside
 //      of a callback.
 //    * If one thread is notifying observers concurrently with an observer
 //      removing itself from the observer list, the notifications will
 //      be silently dropped.
 //
 //   The drawback of the threadsafe observer list is that notifications
 //   are not as real-time as the non-threadsafe version of this class.
 //   Notifications will always be done via PostTask() to another thread,
 //   whereas with the non-thread-safe observer_list, notifications happen
 //   synchronously and immediately.
 //
 //   IMPLEMENTATION NOTES
 //   The ObserverListThreadSafe maintains an ObserverList for each thread
 //   which uses the ThreadSafeObserver.  When Notifying the observers,
 //   we simply call PostTask to each registered thread, and then each thread
 //   will notify its regular ObserverList.
 //
 ///////////////////////////////////////////////////////////////////////////////
 template <class ObserverType>
 class ObserverListThreadSafe
     : public base::RefCountedThreadSafe<ObserverListThreadSafe<ObserverType> > {
  public:
   ObserverListThreadSafe() {}
   ~ObserverListThreadSafe() {
     typename ObserversListMap::const_iterator it;
     for (it = observer_lists_.begin(); it != observer_lists_.end(); ++it)
       delete (*it).second;
     observer_lists_.clear();
   }
   // Add an observer to the list.
   void AddObserver(ObserverType* obs) {
     ObserverList<ObserverType>* list = NULL;
     MessageLoop* loop = MessageLoop::current();
     // TODO(mbelshe): Get rid of this check.  Its needed right now because
     //                Time currently triggers usage of the ObserverList.
     //                And unittests use time without a MessageLoop.
     if (!loop)
       return;  // Some unittests may access this without a message loop.
     {
       AutoLock lock(list_lock_);
       if (observer_lists_.find(loop) == observer_lists_.end())
         observer_lists_[loop] = new ObserverList<ObserverType>();
       list = observer_lists_[loop];
     }
     list->AddObserver(obs);
   }
   // Remove an observer from the list.
   // If there are pending notifications in-transit to the observer, they will
   // be aborted.
   // RemoveObserver MUST be called from the same thread which called
   // AddObserver.
   void RemoveObserver(ObserverType* obs) {
     ObserverList<ObserverType>* list = NULL;
     MessageLoop* loop = MessageLoop::current();
     if (!loop)
       return;  // On shutdown, it is possible that current() is already null.
     {
       AutoLock lock(list_lock_);
       list = observer_lists_[loop];
       if (!list) {
         NOTREACHED() << "RemoveObserver called on for unknown thread";
         return;
       }
       // If we're about to remove the last observer from the list,
       // then we can remove this observer_list entirely.
       if (list->size() == 1)
         observer_lists_.erase(loop);
     }
     list->RemoveObserver(obs);
     // If RemoveObserver is called from a notification, the size will be
     // nonzero.  Instead of deleting here, the NotifyWrapper will delete
     // when it finishes iterating.
     if (list->size() == 0)
       delete list;
   }
   // Notify methods.
   // Make a thread-safe callback to each Observer in the list.
   // Note, these calls are effectively asynchronous.  You cannot assume
   // that at the completion of the Notify call that all Observers have
   // been Notified.  The notification may still be pending delivery.
   template <class Method>
   void Notify(Method m) {
     UnboundMethod<ObserverType, Method, Tuple0> method(m, MakeTuple());
     Notify<Method, Tuple0>(method);
   }
   template <class Method, class A>
   void Notify(Method m, const A &a) {
     UnboundMethod<ObserverType, Method, Tuple1<A> > method(m, MakeTuple(a));
     Notify<Method, Tuple1<A> >(method);
   }
   // TODO(mbelshe):  Add more wrappers for Notify() with more arguments.
  private:
   template <class Method, class Params>
   void Notify(const UnboundMethod<ObserverType, Method, Params>& method) {
     AutoLock lock(list_lock_);
     typename ObserversListMap::iterator it;
     for (it = observer_lists_.begin(); it != observer_lists_.end(); ++it) {
       MessageLoop* loop = (*it).first;
       ObserverList<ObserverType>* list = (*it).second;
       loop->PostTask(FROM_HERE,
           NewRunnableMethod(this,
               &ObserverListThreadSafe<ObserverType>::
                  template NotifyWrapper<Method, Params>, list, method));
     }
   }
   // Wrapper which is called to fire the notifications for each thread's
   // ObserverList.  This function MUST be called on the thread which owns
   // the unsafe ObserverList.
   template <class Method, class Params>
   void NotifyWrapper(ObserverList<ObserverType>* list,
       const UnboundMethod<ObserverType, Method, Params>& method) {
     // Check that this list still needs notifications.
     {
       AutoLock lock(list_lock_);
       typename ObserversListMap::iterator it =
           observer_lists_.find(MessageLoop::current());
       // The ObserverList could have been removed already.  In fact, it could
       // have been removed and then re-added!  If the master list's loop
       // does not match this one, then we do not need to finish this
       // notification.
       if (it == observer_lists_.end() || it->second != list)
         return;
     }
     {
       typename ObserverList<ObserverType>::Iterator it(*list);
       ObserverType* obs;
       while ((obs = it.GetNext()) != NULL)
         method.Run(obs);
     }
     // If there are no more observers on the list, we can now delete it.
     if (list->size() == 0) {
 #ifndef NDEBUG
       {
         AutoLock lock(list_lock_);
         // Verify this list is no longer registered.
         typename ObserversListMap::iterator it =
             observer_lists_.find(MessageLoop::current());
         DCHECK(it == observer_lists_.end() || it->second != list);
       }
 #endif
       delete list;
     }
   }
   typedef std::map<MessageLoop*, ObserverList<ObserverType>*> ObserversListMap;
   // These are marked mutable to facilitate having NotifyAll be const.
   Lock list_lock_;  // Protects the observer_lists_.
   ObserversListMap observer_lists_;
   DISALLOW_EVIL_CONSTRUCTORS(ObserverListThreadSafe);
 };
 } // namespace base
 #endif  // BASE_OBSERVER_LIST_THREADSAFE_H_

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ipc/chromium/src/base/observer_list_threadsafe.h@6474c204b198 (annotated)

ipc/chromium/src/base/observer_list_threadsafe.h