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#ifndef QPID_SYS_BLOCKINGQUEUE_H
#define QPID_SYS_BLOCKINGQUEUE_H
/*
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*
*/
#include "Waitable.h"
#include <queue>
namespace qpid {
namespace sys {
struct QueueClosed {};
template <class T>
class BlockingQueue
{
sys::Waitable lock;
std::queue<T> queue;
bool closed;
public:
BlockingQueue() : closed(false) {}
~BlockingQueue() { close(); }
/** Block until there is a value to pop */
T pop()
{
Waitable::ScopedLock l(lock);
if (!queueWait()) throw QueueClosed();
return popInternal();
}
/** Non-blocking pop. If there is a value set outValue and return
* true, else return false;
*/
bool tryPop(T& outValue) {
Waitable::ScopedLock l(lock);
if (queue.empty()) return false;
outValue = popInternal();
return true;
}
/** Non-blocking pop. If there is a value return it, else return
* valueIfEmpty.
*/
T tryPop(const T& valueIfEmpty=T()) {
T result=valueIfEmpty;
tryPop(result);
return result;
}
/** Push a value onto the queue */
void push(const T& t)
{
Waitable::ScopedLock l(lock);
queue.push(t);
queueNotify(0);
}
/**
* Close the queue. Throws QueueClosed in threads waiting in pop().
* Blocks till all waiting threads have been notified.
*/
void close()
{
Waitable::ScopedLock l(lock);
if (!closed) {
closed = true;
lock.notifyAll();
lock.waitWaiters(); // Ensure no threads are still waiting.
}
}
/** Open a closed queue. */
void open() {
Waitable::ScopedLock l(lock);
closed=false;
}
private:
void queueNotify(size_t ignore) {
if (!queue.empty() && lock.hasWaiters()>ignore)
lock.notify(); // Notify another waiter.
}
bool queueWait() {
Waitable::ScopedWait w(lock);
while (!closed && queue.empty())
lock.wait();
return !queue.empty();
}
T popInternal() {
T t=queue.front();
queue.pop();
queueNotify(1);
return t;
}
};
}}
#endif /*!QPID_SYS_BLOCKINGQUEUE_H*/
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