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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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/db/service_context.h"
#include "mongo/platform/mutex.h"
#include "mongo/stdx/chrono.h"
#include "mongo/stdx/condition_variable.h"
namespace mongo {
/**
* Interface for handling distributed locks.
*
* Usage:
*
* auto scopedDistLock = mgr->lock(...);
*
* if (!scopedDistLock.isOK()) {
* // Did not get lock. scopedLockStatus destructor will not call unlock.
* }
*
* 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:
// Default timeout which will be used if one is not passed to the lock method.
static const Minutes kDefaultLockTimeout;
// Timeout value, which specifies that if the lock is not available immediately, no attempt
// should be made to wait for it to become free.
static const Milliseconds kSingleLockAttemptTimeout;
/**
* RAII type for the local lock.
*/
class ScopedLock {
ScopedLock(const ScopedLock&) = delete;
ScopedLock& operator=(const ScopedLock&) = delete;
public:
ScopedLock(StringData lockName, DistLockManager* distLockManager);
~ScopedLock();
ScopedLock(ScopedLock&& other);
private:
std::string _ns;
DistLockManager* _lockManager;
};
/**
* RAII type for the distributed lock.
*/
class ScopedDistLock {
ScopedDistLock(const ScopedDistLock&) = delete;
ScopedDistLock& operator=(const ScopedDistLock&) = delete;
public:
ScopedDistLock(OperationContext* opCtx,
StringData lockName,
ScopedLock&& scopedLock,
DistLockManager* lockManager);
~ScopedDistLock();
ScopedDistLock(ScopedDistLock&& other);
ScopedDistLock moveToAnotherThread();
void assignNewOpCtx(OperationContext* opCtx);
private:
OperationContext* _opCtx;
std::string _lockName;
ScopedLock _scopedLock;
DistLockManager* _lockManager;
};
virtual ~DistLockManager() = default;
/**
* Retrieves the DistLockManager singleton for the node.
*/
static DistLockManager* get(ServiceContext* service);
static DistLockManager* get(OperationContext* opCtx);
static void create(ServiceContext* service, std::unique_ptr<DistLockManager> distLockManager);
/**
* Performs bootstrapping for the manager. Implementation do not need to guarantee
* thread safety so callers should employ proper synchronization when calling this method.
*/
virtual void startUp() = 0;
/**
* Cleanup the manager's resources. Implementations do not need to guarantee thread safety
* so callers should employ proper synchronization when calling this method.
*/
virtual void shutDown(OperationContext* opCtx) = 0;
/**
* Returns the process ID for this DistLockManager.
*/
virtual std::string getProcessID() = 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.
*/
StatusWith<ScopedDistLock> lock(OperationContext* opCtx,
StringData name,
StringData whyMessage,
Milliseconds waitFor);
/**
* Ensures that two dist lock within the same process will serialise with each other.
*/
ScopedLock lockDirectLocally(OperationContext* opCtx, StringData ns, Milliseconds waitFor);
/**
* Same behavior as lock(...) above, except doesn't return a scoped object, so it is the
* responsibility of the caller to call unlock for the same name.
*
* This is useful for a process running on the config primary after a failover. A lock can be
* immediately reacquired if "lockSessionID" matches that of the lock, rather than waiting for
* the inactive lock to expire.
*/
virtual Status lockDirect(OperationContext* opCtx,
StringData name,
StringData whyMessage,
Milliseconds waitFor) = 0;
/**
* Specialized locking method, which only succeeds if the specified lock name is not held by
* anyone. Uses local write concern and does not attempt to overtake the lock or check whether
* the lock lease has expired.
*
* This method is only used by the Balancer, which re-acquires dist locks while in drain mode.
*/
virtual Status tryLockDirectWithLocalWriteConcern(OperationContext* opCtx,
StringData name,
StringData whyMessage) = 0;
/**
* Unlocks the given lockHandle. Will keep retrying (asynchronously) until the lock is freed or
* some terminal error occurs where a lock cannot be freed (such as a local NotWritablePrimary).
*
* The provided interruptible object can be nullptr in which case the method will not attempt to
* wait for the unlock to be confirmed.
*/
virtual void unlock(Interruptible* intr, StringData name) = 0;
/**
* Makes a best-effort attempt to unlock all locks owned by the given processID.
*/
virtual void unlockAll(OperationContext* opCtx) = 0;
protected:
DistLockManager(OID lockSessionID);
const OID _lockSessionID;
struct NSLock {
stdx::condition_variable cvLocked;
int numWaiting = 1;
bool isInProgress = true;
};
Mutex _mutex = MONGO_MAKE_LATCH("NamespaceSerializer::_mutex");
StringMap<std::shared_ptr<NSLock>> _inProgressMap;
};
} // namespace mongo
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