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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <vespa/vespalib/util/guard.h>
#include <queue>
#include <condition_variable>
namespace vespalib {
template <typename T>
class Queue {
private:
std::queue<T> _q;
std::mutex _lock;
std::condition_variable _cond;
int _waitRead;
int _waitWrite;
uint32_t _maxSize;
bool _closed;
T _nil;
Queue(const Queue &);
Queue &operator=(const Queue &);
public:
Queue(const T &nil, uint32_t maxSize);
~Queue();
void enqueue(const T &entry);
void close();
T dequeue();
};
template <typename T>
Queue<T>::Queue(const T &nil, uint32_t maxSize) :
_q(),
_lock(),
_cond(),
_waitRead(0),
_waitWrite(0),
_maxSize(maxSize),
_closed(false),
_nil(nil)
{
}
template <typename T>
Queue<T>::~Queue() = default;
template <typename T>
void Queue<T>::enqueue(const T &entry) {
std::unique_lock guard(_lock);
while (_q.size() >= _maxSize) {
CounterGuard cntGuard(_waitWrite);
_cond.wait(guard);
}
_q.push(entry);
if (_waitRead > 0) {
_cond.notify_one();
}
}
template <typename T>
void Queue<T>::close() {
std::unique_lock guard(_lock);
_closed = true;
if (_waitRead > 0) {
_cond.notify_one();
}
}
template <typename T>
T Queue<T>::dequeue() {
std::unique_lock guard(_lock);
while (_q.empty() && !_closed) {
CounterGuard cntGuard(_waitRead);
_cond.wait(guard);
}
if (_q.empty()) {
return _nil;
}
T tmp = _q.front();
_q.pop();
if (_waitWrite > 0) {
_cond.notify_one();
}
return tmp;
}
}
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