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/** Copyright 2017 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/stdx/mutex.h"
#include "mongo/util/assert_util.h"
#include <utility>
namespace mongo {
/**
* WithLock is an attestation to pass as an argument to functions that must be called only while
* holding a lock, as a rigorous alternative to an unchecked naming convention and/or stern
* comments. It helps prevent a common usage error.
*
* It may be used to modernize code from (something like) this
*
* // Member _mutex MUST be held when calling this:
* void _clobber_inlock(OperationContext* opCtx) {
* _stuff = makeStuff(opCtx);
* }
*
* into
*
* void _clobber(WithLock, OperationContext* opCtx) {
* _stuff = makeStuff(opCtx);
* }
*
* A call to such a function looks like this:
*
* stdx::lock_guard<stdx::mutex> lk(_mutex);
* _clobber(lk, opCtx); // instead of _clobber_inlock(opCtx)
*
* Note that the formal argument need not (and should not) be named unless it is needed to pass
* the attestation along to another function:
*
* void _clobber(WithLock lock, OperationContext* opCtx) {
* _really_clobber(lock, opCtx);
* }
*
*/
struct WithLock {
template <typename Mutex>
WithLock(stdx::lock_guard<Mutex> const&) noexcept {}
template <typename Mutex>
WithLock(stdx::unique_lock<Mutex> const& lock) noexcept {
invariant(lock.owns_lock());
}
// Add constructors from any other lock types here.
// Pass by value is OK.
WithLock(WithLock const&) noexcept {}
WithLock(WithLock&&) noexcept {}
// No assigning WithLocks.
void operator=(WithLock const&) = delete;
void operator=(WithLock&&) = delete;
// No moving a lock_guard<> or unique_lock<> in.
template <typename Mutex>
WithLock(stdx::lock_guard<Mutex>&&) = delete;
template <typename Mutex>
WithLock(stdx::unique_lock<Mutex>&&) = delete;
/*
* Produces a WithLock without benefit of any actual lock, for use in cases where a lock is not
* really needed, such as in many (but not all!) constructors.
*/
static WithLock withoutLock() noexcept {
return {};
}
private:
WithLock() noexcept = default;
};
} // namespace mongo
namespace std {
// No moving a WithLock:
template <>
mongo::WithLock&& move<mongo::WithLock>(mongo::WithLock&&) noexcept = delete;
} // namespace std
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