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// Copyright 2018 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 MEDIA_BASE_CALLBACK_REGISTRY_H_
#define MEDIA_BASE_CALLBACK_REGISTRY_H_
#include <stdint.h>
#include <map>
#include <memory>
#include "base/callback.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/synchronization/lock.h"
#include "base/thread_annotations.h"
#include "media/base/bind_to_current_loop.h"
namespace media {
// A class that keeps a callback registered. The callback will be unregistered
// upon destruction of this object.
class CallbackRegistration {
public:
CallbackRegistration() = default;
virtual ~CallbackRegistration() = default;
private:
DISALLOW_COPY_AND_ASSIGN(CallbackRegistration);
};
template <typename Sig>
class CallbackRegistry;
// A helper class that can register, unregister callbacks, and notify registered
// callbacks. This class is thread safe: all methods can be called on any
// thread. The CallbackRegistry must outlive all CallbackRegistrations returned
// by Register().
// TODO(xhwang): This class is similar to base::RepeatingCallbackList, but is
// simpler, and provides thread safety. Consider merging these two.
template <typename... Args>
class CallbackRegistry<void(Args...)> {
public:
using CallbackType = base::RepeatingCallback<void(Args...)>;
CallbackRegistry() = default;
~CallbackRegistry() = default;
std::unique_ptr<CallbackRegistration> Register(CallbackType cb)
WARN_UNUSED_RESULT {
base::AutoLock lock(lock_);
DCHECK(cb);
uint32_t registration_id = ++next_registration_id_;
DVLOG(1) << __func__ << ": registration_id = " << registration_id;
// Use BindToCurrentLoop so that the callbacks are always posted to the
// thread where Register() is called. Also, this helps avoid reentrancy
// and deadlock issues, e.g. Register() is called in one of the callbacks.
callbacks_[registration_id] = BindToCurrentLoop(std::move(cb));
return std::make_unique<RegistrationImpl>(this, registration_id);
}
void Notify(Args&&... args) {
DVLOG(1) << __func__;
base::AutoLock lock(lock_);
for (auto const& entry : callbacks_)
entry.second.Run(std::forward<Args>(args)...);
}
private:
class RegistrationImpl : public CallbackRegistration {
public:
RegistrationImpl(CallbackRegistry<void(Args...)>* registry,
uint32_t registration_id)
: registry_(registry), registration_id_(registration_id) {}
~RegistrationImpl() override { registry_->Unregister(registration_id_); }
private:
CallbackRegistry<void(Args...)>* registry_ = nullptr;
uint32_t registration_id_ = 0;
DISALLOW_COPY_AND_ASSIGN(RegistrationImpl);
};
void Unregister(uint32_t registration_id) {
DVLOG(1) << __func__ << ": registration_id = " << registration_id;
base::AutoLock lock(lock_);
size_t num_callbacks_removed = callbacks_.erase(registration_id);
DCHECK_EQ(num_callbacks_removed, 1u);
}
base::Lock lock_;
uint32_t next_registration_id_ GUARDED_BY(lock_) = 0;
std::map<uint32_t, CallbackType> callbacks_ GUARDED_BY(lock_);
DISALLOW_COPY_AND_ASSIGN(CallbackRegistry);
};
using ClosureRegistry = CallbackRegistry<void()>;
} // namespace media
#endif // MEDIA_BASE_CALLBACK_REGISTRY_H_
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