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// Copyright 2013 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_CALLBACK_LIST_H_
#define BASE_CALLBACK_LIST_H_
#include <list>
#include "base/basictypes.h"
#include "base/callback.h"
#include "base/callback_internal.h"
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
// OVERVIEW:
//
// A container for a list of callbacks. Unlike a normal STL vector or list,
// this container can be modified during iteration without invalidating the
// iterator. It safely handles the case of a callback removing itself
// or another callback from the list while callbacks are being run.
//
// TYPICAL USAGE:
//
// class MyWidget {
// public:
// ...
//
// typedef base::Callback<void(const Foo&)> OnFooCallback;
//
// scoped_ptr<base::CallbackList<void(const Foo&)>::Subscription>
// RegisterCallback(const OnFooCallback& cb) {
// return callback_list_.Add(cb);
// }
//
// private:
// void NotifyFoo(const Foo& foo) {
// callback_list_.Notify(foo);
// }
//
// base::CallbackList<void(const Foo&)> callback_list_;
//
// DISALLOW_COPY_AND_ASSIGN(MyWidget);
// };
//
//
// class MyWidgetListener {
// public:
// MyWidgetListener::MyWidgetListener() {
// foo_subscription_ = MyWidget::GetCurrent()->RegisterCallback(
// base::Bind(&MyWidgetListener::OnFoo, this)));
// }
//
// MyWidgetListener::~MyWidgetListener() {
// // Subscription gets deleted automatically and will deregister
// // the callback in the process.
// }
//
// private:
// void OnFoo(const Foo& foo) {
// // Do something.
// }
//
// scoped_ptr<base::CallbackList<void(const Foo&)>::Subscription>
// foo_subscription_;
//
// DISALLOW_COPY_AND_ASSIGN(MyWidgetListener);
// };
namespace base {
namespace internal {
template <typename CallbackType>
class CallbackListBase {
public:
class Subscription {
public:
Subscription(CallbackListBase<CallbackType>* list,
typename std::list<CallbackType>::iterator iter)
: list_(list),
iter_(iter) {
}
~Subscription() {
if (list_->active_iterator_count_) {
iter_->Reset();
} else {
list_->callbacks_.erase(iter_);
if (!list_->removal_callback_.is_null())
list_->removal_callback_.Run();
}
}
private:
CallbackListBase<CallbackType>* list_;
typename std::list<CallbackType>::iterator iter_;
DISALLOW_COPY_AND_ASSIGN(Subscription);
};
// Add a callback to the list. The callback will remain registered until the
// returned Subscription is destroyed, which must occur before the
// CallbackList is destroyed.
scoped_ptr<Subscription> Add(const CallbackType& cb) WARN_UNUSED_RESULT {
DCHECK(!cb.is_null());
return scoped_ptr<Subscription>(
new Subscription(this, callbacks_.insert(callbacks_.end(), cb)));
}
// Sets a callback which will be run when a subscription list is changed.
void set_removal_callback(const Closure& callback) {
removal_callback_ = callback;
}
// Returns true if there are no subscriptions. This is only valid to call when
// not looping through the list.
bool empty() {
DCHECK_EQ(0, active_iterator_count_);
return callbacks_.empty();
}
protected:
// An iterator class that can be used to access the list of callbacks.
class Iterator {
public:
explicit Iterator(CallbackListBase<CallbackType>* list)
: list_(list),
list_iter_(list_->callbacks_.begin()) {
++list_->active_iterator_count_;
}
Iterator(const Iterator& iter)
: list_(iter.list_),
list_iter_(iter.list_iter_) {
++list_->active_iterator_count_;
}
~Iterator() {
if (list_ && --list_->active_iterator_count_ == 0) {
list_->Compact();
}
}
CallbackType* GetNext() {
while ((list_iter_ != list_->callbacks_.end()) && list_iter_->is_null())
++list_iter_;
CallbackType* cb = NULL;
if (list_iter_ != list_->callbacks_.end()) {
cb = &(*list_iter_);
++list_iter_;
}
return cb;
}
private:
CallbackListBase<CallbackType>* list_;
typename std::list<CallbackType>::iterator list_iter_;
};
CallbackListBase() : active_iterator_count_(0) {}
~CallbackListBase() {
DCHECK_EQ(0, active_iterator_count_);
DCHECK_EQ(0U, callbacks_.size());
}
// Returns an instance of a CallbackListBase::Iterator which can be used
// to run callbacks.
Iterator GetIterator() {
return Iterator(this);
}
// Compact the list: remove any entries which were NULLed out during
// iteration.
void Compact() {
typename std::list<CallbackType>::iterator it = callbacks_.begin();
bool updated = false;
while (it != callbacks_.end()) {
if ((*it).is_null()) {
updated = true;
it = callbacks_.erase(it);
} else {
++it;
}
if (updated && !removal_callback_.is_null())
removal_callback_.Run();
}
}
private:
std::list<CallbackType> callbacks_;
int active_iterator_count_;
Closure removal_callback_;
DISALLOW_COPY_AND_ASSIGN(CallbackListBase);
};
} // namespace internal
template <typename Sig> class CallbackList;
template <typename... Args>
class CallbackList<void(Args...)>
: public internal::CallbackListBase<Callback<void(Args...)> > {
public:
typedef Callback<void(Args...)> CallbackType;
CallbackList() {}
void Notify(
typename internal::CallbackParamTraits<Args>::ForwardType... args) {
typename internal::CallbackListBase<CallbackType>::Iterator it =
this->GetIterator();
CallbackType* cb;
while ((cb = it.GetNext()) != NULL) {
cb->Run(args...);
}
}
private:
DISALLOW_COPY_AND_ASSIGN(CallbackList);
};
} // namespace base
#endif // BASE_CALLBACK_LIST_H_
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