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// Copyright (c) 2011 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_H__
#define BASE_OBSERVER_LIST_H__
#include <algorithm>
#include <limits>
#include <vector>
#include "base/basictypes.h"
#include "base/logging.h"
#include "base/memory/weak_ptr.h"
///////////////////////////////////////////////////////////////////////////////
//
// OVERVIEW:
//
// A container for a list of observers. Unlike a normal STL vector or list,
// this container can be modified during iteration without invalidating the
// iterator. So, it safely handles the case of an observer removing itself
// or other observers from the list while observers are being notified.
//
// TYPICAL USAGE:
//
// class MyWidget {
// public:
// ...
//
// class Observer {
// public:
// virtual void OnFoo(MyWidget* w) = 0;
// virtual void OnBar(MyWidget* w, int x, int y) = 0;
// };
//
// void AddObserver(Observer* obs) {
// observer_list_.AddObserver(obs);
// }
//
// void RemoveObserver(Observer* obs) {
// observer_list_.RemoveObserver(obs);
// }
//
// void NotifyFoo() {
// FOR_EACH_OBSERVER(Observer, observer_list_, OnFoo(this));
// }
//
// void NotifyBar(int x, int y) {
// FOR_EACH_OBSERVER(Observer, observer_list_, OnBar(this, x, y));
// }
//
// private:
// ObserverList<Observer> observer_list_;
// };
//
//
///////////////////////////////////////////////////////////////////////////////
template <typename ObserverType>
class ObserverListThreadSafe;
template <class ObserverType>
class ObserverListBase
: public base::SupportsWeakPtr<ObserverListBase<ObserverType> > {
public:
// Enumeration of which observers are notified.
enum NotificationType {
// Specifies that any observers added during notification are notified.
// This is the default type if non type is provided to the constructor.
NOTIFY_ALL,
// Specifies that observers added while sending out notification are not
// notified.
NOTIFY_EXISTING_ONLY
};
// An iterator class that can be used to access the list of observers. See
// also the FOR_EACH_OBSERVER macro defined below.
class Iterator {
public:
Iterator(ObserverListBase<ObserverType>& list)
: list_(list.AsWeakPtr()),
index_(0),
max_index_(list.type_ == NOTIFY_ALL ?
std::numeric_limits<size_t>::max() :
list.observers_.size()) {
++list_->notify_depth_;
}
~Iterator() {
if (list_ && --list_->notify_depth_ == 0)
list_->Compact();
}
ObserverType* GetNext() {
if (!list_)
return NULL;
ListType& observers = list_->observers_;
// Advance if the current element is null
size_t max_index = std::min(max_index_, observers.size());
while (index_ < max_index && !observers[index_])
++index_;
return index_ < max_index ? observers[index_++] : NULL;
}
private:
base::WeakPtr<ObserverListBase<ObserverType> > list_;
size_t index_;
size_t max_index_;
};
ObserverListBase() : notify_depth_(0), type_(NOTIFY_ALL) {}
explicit ObserverListBase(NotificationType type)
: notify_depth_(0), 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 (std::find(observers_.begin(), observers_.end(), obs)
!= observers_.end()) {
NOTREACHED() << "Observers can only be added once!";
return;
}
observers_.push_back(obs);
}
// Remove an observer from the list if it is in the list.
void RemoveObserver(ObserverType* obs) {
typename ListType::iterator it =
std::find(observers_.begin(), observers_.end(), obs);
if (it != observers_.end()) {
if (notify_depth_) {
*it = 0;
} else {
observers_.erase(it);
}
}
}
bool HasObserver(ObserverType* observer) const {
for (size_t i = 0; i < observers_.size(); ++i) {
if (observers_[i] == observer)
return true;
}
return false;
}
void Clear() {
if (notify_depth_) {
for (typename ListType::iterator it = observers_.begin();
it != observers_.end(); ++it) {
*it = 0;
}
} else {
observers_.clear();
}
}
size_t size() const { return observers_.size(); }
protected:
void Compact() {
observers_.erase(
std::remove(observers_.begin(), observers_.end(),
static_cast<ObserverType*>(NULL)), observers_.end());
}
private:
friend class ObserverListThreadSafe<ObserverType>;
typedef std::vector<ObserverType*> ListType;
ListType observers_;
int notify_depth_;
NotificationType type_;
friend class ObserverListBase::Iterator;
DISALLOW_COPY_AND_ASSIGN(ObserverListBase);
};
template <class ObserverType, bool check_empty = false>
class ObserverList : public ObserverListBase<ObserverType> {
public:
typedef typename ObserverListBase<ObserverType>::NotificationType
NotificationType;
ObserverList() {}
explicit ObserverList(NotificationType type)
: ObserverListBase<ObserverType>(type) {}
~ObserverList() {
// When check_empty is true, assert that the list is empty on destruction.
if (check_empty) {
ObserverListBase<ObserverType>::Compact();
DCHECK_EQ(ObserverListBase<ObserverType>::size(), 0U);
}
}
bool might_have_observers() const {
return ObserverListBase<ObserverType>::size() != 0;
}
};
#define FOR_EACH_OBSERVER(ObserverType, observer_list, func) \
do { \
if ((observer_list).might_have_observers()) { \
ObserverListBase<ObserverType>::Iterator it(observer_list); \
ObserverType* obs; \
while ((obs = it.GetNext()) != NULL) \
obs->func; \
} \
} while (0)
#endif // BASE_OBSERVER_LIST_H__
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