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// -*- mode: c++; c-file-style: "k&r"; c-basic-offset: 4 -*-
// vim: set ts=4 sw=4:
/***********************************************************************
*
* Simple multi-reader, single-writer lock server.
*
* Copyright 2015 Irene Zhang <iyzhang@cs.washington.edu>
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use, copy,
* modify, merge, publish, distribute, sublicense, and/or sell copies
* of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*
**********************************************************************/
#ifndef _LOCK_SERVER_H_
#define _LOCK_SERVER_H_
#include "lib/assert.h"
#include "lib/message.h"
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#include <sys/time.h>
#include <map>
#include <queue>
#include <string>
#include <vector>
#include <unordered_map>
#include <unordered_set>
#define LOCK_WAIT_TIMEOUT 5000
class LockServer
{
public:
LockServer();
~LockServer();
bool lockForRead(const std::string &lock, uint64_t requester);
bool lockForWrite(const std::string &lock, uint64_t requester);
void releaseForRead(const std::string &lock, uint64_t holder);
void releaseForWrite(const std::string &lock, uint64_t holder);
private:
enum LockState {
UNLOCKED,
LOCKED_FOR_READ,
LOCKED_FOR_WRITE,
LOCKED_FOR_READ_WRITE
};
struct Waiter {
bool write;
struct timeval waitTime;
Waiter() {write = false;}
Waiter(bool w) {
gettimeofday(&waitTime, NULL);
write = w;
}
bool checkTimeout(const struct timeval &now);
};
struct Lock {
LockState state;
std::unordered_set<uint64_t> holders;
std::queue<uint64_t> waitQ;
std::map<uint64_t, Waiter> waiters;
Lock() {
state = UNLOCKED;
};
void waitForLock(uint64_t requester, bool write);
bool tryAcquireLock(uint64_t requester, bool write);
bool isWriteNext();
};
/* Global store which keep key -> (timestamp, value) list. */
std::unordered_map<std::string, Lock> locks;
uint64_t readers;
uint64_t writers;
};
#endif /* _LOCK_SERVER_H_ */