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// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <vector>
#include <boost/noncopyable.hpp>
#include <boost/thread/locks.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/thread/condition_variable.hpp>
namespace vespalib {
/* Blocks a writer from being called while readers are active and vice versa.
* This is only intended to be used by a single writer.
*/
class BlockWriterMutex : boost::noncopyable {
typedef boost::mutex ReadersMutex;
ReadersMutex _readersMutex;
int _readers;
boost::condition_variable _noReaders;
void lockImpl(int sign) {
boost::unique_lock<ReadersMutex> readersLock(_readersMutex);
while ((sign*_readers) > 0)
_noReaders.wait(readersLock);
_readers -= sign;
}
void unlockImpl(int sign) {
ReadersMutex::scoped_lock readersLock(_readersMutex);
_readers += sign;
if (_readers == 0)
_noReaders.notify_all();
}
public:
typedef boost::shared_lock<BlockWriterMutex> ReaderLock;
typedef boost::unique_lock<BlockWriterMutex> WriterLock;
BlockWriterMutex()
:_readers(0)
{}
void lock() {
lockImpl(1);
}
void unlock() {
unlockImpl(1);
}
void lock_shared() {
lockImpl(-1);
}
void unlock_shared() {
unlockImpl(-1);
}
};
} //namespace vespalib
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