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// distlock.h
/* Copyright 2009 10gen Inc.
*
* Licensed 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.
*/
#pragma once
#include "../pch.h"
#include "dbclient.h"
#include "connpool.h"
#include "redef_macros.h"
#include "syncclusterconnection.h"
namespace mongo {
/**
* The distributed lock is a configdb backed way of synchronizing system-wide tasks. A task must be identified by a
* unique name across the system (e.g., "balancer"). A lock is taken by writing a document in the configdb's locks
* collection with that name.
*
* To be maintained, each taken lock needs to be revalidaded ("pinged") within a pre-established amount of time. This
* class does this maintenance automatically once a DistributedLock object was constructed.
*/
class DistributedLock {
public:
/**
* The constructor does not connect to the configdb yet and constructing does not mean the lock was acquired.
* Construction does trigger a lock "pinging" mechanism, though.
*
* @param conn address of config(s) server(s)
* @param name identifier for the lock
* @param takeoverMinutes how long can the log go "unpinged" before a new attempt to lock steals it (in minutes)
*/
DistributedLock( const ConnectionString& conn , const string& name , unsigned takeoverMinutes = 15 );
/**
* Attempts to aquire 'this' lock, checking if it could or should be stolen from the previous holder. Please
* consider using the dist_lock_try construct to acquire this lock in an exception safe way.
*
* @param why human readable description of why the lock is being taken (used to log)
* @param other configdb's lock document that is currently holding the lock, if lock is taken
* @return true if it managed to grab the lock
*/
bool lock_try( string why , BSONObj * other = 0 );
/**
* Releases a previously taken lock.
*/
void unlock();
private:
ConnectionString _conn;
string _name;
unsigned _takeoverMinutes;
string _ns;
BSONObj _id;
};
class dist_lock_try {
public:
dist_lock_try( DistributedLock * lock , string why )
: _lock(lock) {
_got = _lock->lock_try( why , &_other );
}
~dist_lock_try() {
if ( _got ) {
_lock->unlock();
}
}
bool got() const { return _got; }
BSONObj other() const { return _other; }
private:
DistributedLock * _lock;
bool _got;
BSONObj _other;
};
}
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