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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/db/concurrency/d_concurrency.h"
#include "mongo/stdx/variant.h"
namespace mongo {
/**
* RAII-style class that locks a sharding state object using the state object's ResourceMutex. The
* lock will be created and acquired on construction. The lock will be dismissed upon destruction
* of the sharding state object.
*/
template <class ShardingState>
class ShardingStateLock {
public:
/**
* Locks the sharding state object with the sharding state object's ResourceMutex in MODE_IS.
* When the object goes out of scope, the ResourceMutex will be unlocked.
*/
static ShardingStateLock<ShardingState> lockShared(OperationContext* opCtx,
ShardingState* state);
/**
* Follows the same functionality as the ShardingStateLock lock method, except that
* lockExclusive takes the ResourceMutex in MODE_X.
*/
static ShardingStateLock<ShardingState> lockExclusive(OperationContext* opCtx,
ShardingState* state);
private:
using StateLock = stdx::variant<Lock::SharedLock, Lock::ExclusiveLock>;
ShardingStateLock<ShardingState>(OperationContext* opCtx,
ShardingState* state,
LockMode lockMode);
// The lock created and locked upon construction of a ShardingStateLock object. It locks the
// ResourceMutex taken from the ShardingState class, passed in on construction.
StateLock _lock;
};
template <class ShardingState>
ShardingStateLock<ShardingState>::ShardingStateLock(OperationContext* opCtx,
ShardingState* state,
LockMode lockMode)
: _lock([&]() -> StateLock {
invariant(lockMode == MODE_IS || lockMode == MODE_X);
return (
lockMode == MODE_IS
? StateLock(Lock::SharedLock(opCtx->lockState(), state->_stateChangeMutex))
: StateLock(Lock::ExclusiveLock(opCtx->lockState(), state->_stateChangeMutex)));
}()) {}
template <class ShardingState>
ShardingStateLock<ShardingState> ShardingStateLock<ShardingState>::lockShared(
OperationContext* opCtx, ShardingState* state) {
return ShardingStateLock(opCtx, state, MODE_IS);
}
template <class ShardingState>
ShardingStateLock<ShardingState> ShardingStateLock<ShardingState>::lockExclusive(
OperationContext* opCtx, ShardingState* state) {
return ShardingStateLock(opCtx, state, MODE_X);
}
} // namespace mongo
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