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/**
* Copyright (C) 2015 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include "mongo/base/string_data.h"
#include "mongo/bson/oid.h"
#include "mongo/stdx/chrono.h"
namespace mongo {
using DistLockHandle = OID;
class Status;
template <typename T> class StatusWith;
/**
* Interface for handling distributed locks.
*
* Usage:
*
* auto scopedDistLock = mgr->lock(...);
*
* if (!scopedDistLock.isOK()) {
* // Did not get lock. scopedLockStatus destructor will not call unlock.
* }
*
* // To check if lock is still owned:
* auto status = scopedDistLock.getValue().checkStatus();
*
* if (!status.isOK()) {
* // Someone took over the lock! Unlock will still be called at destructor, but will
* // practically be a no-op since it doesn't own the lock anymore.
* }
*/
class DistLockManager {
public:
static const stdx::chrono::milliseconds kDefaultSingleLockAttemptTimeout;
static const stdx::chrono::milliseconds kDefaultLockRetryInterval;
/**
* RAII type for distributed lock. Not meant to be shared across multiple threads.
*/
class ScopedDistLock {
MONGO_DISALLOW_COPYING(ScopedDistLock);
public:
ScopedDistLock(); // TODO: SERVER-18007
ScopedDistLock(DistLockHandle lockHandle, DistLockManager* lockManager);
~ScopedDistLock();
ScopedDistLock(ScopedDistLock&& other);
ScopedDistLock& operator=(ScopedDistLock&& other);
/**
* Checks whether the lock is still being held by querying the config server.
*/
Status checkStatus();
private:
DistLockHandle _lockID;
DistLockManager* _lockManager; // Not owned here.
};
virtual ~DistLockManager() = default;
virtual void startUp() = 0;
virtual void shutDown() = 0;
/**
* Tries multiple times to lock, using the specified lock try interval, until
* a certain amount of time has passed or when any error that is not LockBusy
* occurred.
*
* waitFor = 0 indicates there should only be one attempt to acquire the lock, and
* no waiting.
* waitFor = -1 indicates we should retry indefinitely.
*
* Returns OK if the lock was successfully acquired.
* Returns ErrorCodes::DistributedClockSkewed when a clock skew is detected.
* Returns ErrorCodes::LockBusy if the lock is being held.
*/
virtual StatusWith<ScopedDistLock> lock(
StringData name,
StringData whyMessage,
stdx::chrono::milliseconds waitFor = kDefaultSingleLockAttemptTimeout,
stdx::chrono::milliseconds lockTryInterval = kDefaultLockRetryInterval) = 0;
protected:
/**
* Unlocks the given lockHandle. Will attempt to retry again later if the config
* server is not reachable.
*/
virtual void unlock(const DistLockHandle& lockHandle) = 0;
/**
* Checks if the lockHandle still exists in the config server.
*/
virtual Status checkStatus(const DistLockHandle& lockHandle) = 0;
};
}
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