The Tor Browser: security/sandbox/chromium/base/observer_list

security/sandbox/chromium/base/observer_list_threadsafe.h@b8a032363ba2 (annotated)

security/sandbox/chromium/base/observer_list_threadsafe.h

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 // 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_OBSERVER_LIST_THREADSAFE_H_
 #define BASE_OBSERVER_LIST_THREADSAFE_H_
 #include <algorithm>
 #include <map>
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop/message_loop.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "base/observer_list.h"
 #include "base/stl_util.h"
 #include "base/threading/platform_thread.h"
 ///////////////////////////////////////////////////////////////////////////////
 //
 // 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 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.
 //
 ///////////////////////////////////////////////////////////////////////////////
 // Forward declaration for ObserverListThreadSafeTraits.
 template <class ObserverType>
 class ObserverListThreadSafe;
 // An UnboundMethod is a wrapper for a method where the actual object is
 // provided at Run dispatch time.
 template <class T, class Method, class Params>
 class UnboundMethod {
  public:
   UnboundMethod(Method m, const Params& p) : m_(m), p_(p) {
     COMPILE_ASSERT(
         (base::internal::ParamsUseScopedRefptrCorrectly<Params>::value),
         badunboundmethodparams);
   }
   void Run(T* obj) const {
     DispatchToMethod(obj, m_, p_);
   }
  private:
   Method m_;
   Params p_;
 };
 // This class is used to work around VS2005 not accepting:
 //
 // friend class
 //     base::RefCountedThreadSafe<ObserverListThreadSafe<ObserverType> >;
 //
 // Instead of friending the class, we could friend the actual function
 // which calls delete.  However, this ends up being
 // RefCountedThreadSafe::DeleteInternal(), which is private.  So we
 // define our own templated traits class so we can friend it.
 template <class T>
 struct ObserverListThreadSafeTraits {
   static void Destruct(const ObserverListThreadSafe<T>* x) {
     delete x;
   }
 };
 template <class ObserverType>
 class ObserverListThreadSafe
     : public base::RefCountedThreadSafe<
         ObserverListThreadSafe<ObserverType>,
         ObserverListThreadSafeTraits<ObserverType> > {
  public:
   typedef typename ObserverList<ObserverType>::NotificationType
       NotificationType;
   ObserverListThreadSafe()
       : type_(ObserverListBase<ObserverType>::NOTIFY_ALL) {}
   explicit ObserverListThreadSafe(NotificationType type) : type_(type) {}
   // Add an observer to the list.  An observer should not be added to
   // the same list more than once.
   void AddObserver(ObserverType* obs) {
     // If there is not a current MessageLoop, it is impossible to notify on it,
     // so do not add the observer.
     if (!base::MessageLoop::current())
       return;
     ObserverList<ObserverType>* list = NULL;
     base::PlatformThreadId thread_id = base::PlatformThread::CurrentId();
     {
       base::AutoLock lock(list_lock_);
       if (observer_lists_.find(thread_id) == observer_lists_.end())
         observer_lists_[thread_id] = new ObserverListContext(type_);
       list = &(observer_lists_[thread_id]->list);
     }
     list->AddObserver(obs);
   }
   // Remove an observer from the list if it is in the list.
   // If there are pending notifications in-transit to the observer, they will
   // be aborted.
   // If the observer to be removed is in the list, RemoveObserver MUST
   // be called from the same thread which called AddObserver.
   void RemoveObserver(ObserverType* obs) {
     ObserverListContext* context = NULL;
     ObserverList<ObserverType>* list = NULL;
     base::PlatformThreadId thread_id = base::PlatformThread::CurrentId();
     {
       base::AutoLock lock(list_lock_);
       typename ObserversListMap::iterator it = observer_lists_.find(thread_id);
       if (it == observer_lists_.end()) {
         // This will happen if we try to remove an observer on a thread
         // we never added an observer for.
         return;
       }
       context = it->second;
       list = &context->list;
       // If we're about to remove the last observer from the list,
       // then we can remove this observer_list entirely.
       if (list->HasObserver(obs) && list->size() == 1)
         observer_lists_.erase(it);
     }
     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 context;
   }
   // Verifies that the list is currently empty (i.e. there are no observers).
   void AssertEmpty() const {
     base::AutoLock lock(list_lock_);
     DCHECK(observer_lists_.empty());
   }
   // 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);
   }
   template <class Method, class A, class B>
   void Notify(Method m, const A& a, const B& b) {
     UnboundMethod<ObserverType, Method, Tuple2<A, B> > method(
         m, MakeTuple(a, b));
     Notify<Method, Tuple2<A, B> >(method);
   }
   template <class Method, class A, class B, class C>
   void Notify(Method m, const A& a, const B& b, const C& c) {
     UnboundMethod<ObserverType, Method, Tuple3<A, B, C> > method(
         m, MakeTuple(a, b, c));
     Notify<Method, Tuple3<A, B, C> >(method);
   }
   template <class Method, class A, class B, class C, class D>
   void Notify(Method m, const A& a, const B& b, const C& c, const D& d) {
     UnboundMethod<ObserverType, Method, Tuple4<A, B, C, D> > method(
         m, MakeTuple(a, b, c, d));
     Notify<Method, Tuple4<A, B, C, D> >(method);
   }
   // TODO(mbelshe):  Add more wrappers for Notify() with more arguments.
  private:
   // See comment above ObserverListThreadSafeTraits' definition.
   friend struct ObserverListThreadSafeTraits<ObserverType>;
   struct ObserverListContext {
     explicit ObserverListContext(NotificationType type)
         : loop(base::MessageLoopProxy::current()),
           list(type) {
     }
     scoped_refptr<base::MessageLoopProxy> loop;
     ObserverList<ObserverType> list;
     DISALLOW_COPY_AND_ASSIGN(ObserverListContext);
   };
   ~ObserverListThreadSafe() {
     STLDeleteValues(&observer_lists_);
   }
   template <class Method, class Params>
   void Notify(const UnboundMethod<ObserverType, Method, Params>& method) {
     base::AutoLock lock(list_lock_);
     typename ObserversListMap::iterator it;
     for (it = observer_lists_.begin(); it != observer_lists_.end(); ++it) {
       ObserverListContext* context = (*it).second;
       context->loop->PostTask(
           FROM_HERE,
           base::Bind(&ObserverListThreadSafe<ObserverType>::
               template NotifyWrapper<Method, Params>, this, context, 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(ObserverListContext* context,
       const UnboundMethod<ObserverType, Method, Params>& method) {
     // Check that this list still needs notifications.
     {
       base::AutoLock lock(list_lock_);
       typename ObserversListMap::iterator it =
           observer_lists_.find(base::PlatformThread::CurrentId());
       // 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 != context)
         return;
     }
     {
       typename ObserverList<ObserverType>::Iterator it(context->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 (context->list.size() == 0) {
       {
         base::AutoLock lock(list_lock_);
         // Remove |list| if it's not already removed.
         // This can happen if multiple observers got removed in a notification.
         // See http://crbug.com/55725.
         typename ObserversListMap::iterator it =
             observer_lists_.find(base::PlatformThread::CurrentId());
         if (it != observer_lists_.end() && it->second == context)
           observer_lists_.erase(it);
       }
       delete context;
     }
   }
   // Key by PlatformThreadId because in tests, clients can attempt to remove
   // observers without a MessageLoop. If this were keyed by MessageLoop, that
   // operation would be silently ignored, leaving garbage in the ObserverList.
   typedef std::map<base::PlatformThreadId, ObserverListContext*>
       ObserversListMap;
   mutable base::Lock list_lock_;  // Protects the observer_lists_.
   ObserversListMap observer_lists_;
   const NotificationType type_;
   DISALLOW_COPY_AND_ASSIGN(ObserverListThreadSafe);
 };
 #endif  // BASE_OBSERVER_LIST_THREADSAFE_H_

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security/sandbox/chromium/base/observer_list_threadsafe.h@b8a032363ba2 (annotated)

security/sandbox/chromium/base/observer_list_threadsafe.h