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

--1:000000000000
+:e3a61b8e5e6f
+// 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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comparison: security/sandbox/chromium/base/observer_list_threadsafe.h

security/sandbox/chromium/base/observer_list_threadsafe.h