pulsar-client-cpp/lib/Future.h

/**
 * Copyright 2016 Yahoo Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef LIB_FUTURE_H_
#define LIB_FUTURE_H_

#include <boost/function.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/thread/condition_variable.hpp>
#include <boost/make_shared.hpp>

#include <list>

#pragma GCC visibility push(default)

typedef boost::unique_lock<boost::mutex> Lock;

namespace pulsar {

template<typename Result, typename Type>
struct InternalState {
    boost::mutex mutex;
    boost::condition_variable condition;
    Result result;
    Type value;
    bool complete;

    std::list<typename boost::function<void(Result, const Type&)> > listeners;
};

template<typename Result, typename Type>
class Future {
 public:
    typedef boost::function<void(Result, const Type&)> ListenerCallback;

    Future& addListener(ListenerCallback callback) {
        InternalState<Result, Type>* state = state_.get();
        Lock lock(state->mutex);

        if (state->complete) {
            lock.unlock();
            callback(state->result, state->value);
        } else {
            state->listeners.push_back(callback);
        }

        return *this;
    }

    Result get(Type& result) {
        InternalState<Result, Type>* state = state_.get();
        Lock lock(state->mutex);

        if (!state->complete) {
            // Wait for result
            while (!state->complete) {
                state->condition.wait(lock);
            }
        }

        result = state->value;
        return state->result;
    }

 private:
    typedef boost::shared_ptr<InternalState<Result, Type> > InternalStatePtr;
    Future(InternalStatePtr state)
            : state_(state) {
    }

    boost::shared_ptr<InternalState<Result, Type> > state_;

    template<typename U, typename V>
    friend class Promise;
};

template<typename Result, typename Type>
class Promise {
 public:
    Promise()
            : state_(boost::make_shared<InternalState<Result, Type> >()) {
    }

    bool setValue(const Type& value) {
        InternalState<Result, Type>* state = state_.get();
        Lock lock(state->mutex);

        if (state->complete) {
            return false;
        }

        state->value = value;
        state->result = Result();
        state->complete = true;

        typename std::list<ListenerCallback>::iterator it;
        for (it = state->listeners.begin(); it != state->listeners.end(); ++it) {
            ListenerCallback& callback = *it;
            callback(state->result, state->value);
        }

        state->listeners.clear();
        state->condition.notify_all();
        return true;
    }

    bool setFailed(Result result) {
        InternalState<Result, Type>* state = state_.get();
        Lock lock(state->mutex);

        if (state->complete) {
            return false;
        }

        state->result = result;
        state->complete = true;

        typename std::list<ListenerCallback>::iterator it;
        for (it = state->listeners.begin(); it != state->listeners.end(); ++it) {
            ListenerCallback& callback = *it;
            callback(state->result, state->value);
        }

        state->listeners.clear();
        state->condition.notify_all();
        return true;
    }

    bool isComplete() const {
        InternalState<Result, Type>* state = state_.get();
        Lock lock(state->mutex);
        return state->complete;
    }

    Future<Result, Type> getFuture() const {
        return Future<Result, Type>(state_);
    }

 private:
    typedef boost::function<void(Result, const Type&)> ListenerCallback;
    boost::shared_ptr<InternalState<Result, Type> > state_;
};

class Void {
};

} /* namespace pulsar */

#pragma GCC visibility pop

#endif /* LIB_FUTURE_H_ */