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/**
* Copyright (C) 2022-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 <boost/optional.hpp>
#include "mongo/util/assert_util_core.h"
#include "mongo/util/tick_source.h"
namespace mongo {
class SemaphoreTicketHolder;
class FifoTicketHolder;
/**
* Move-only token that gets generated when a ticket is acquired and has to be marked invalid when
* it is released. Only TicketHolders can create and release valid Tickets.
*/
class Ticket {
friend class SemaphoreTicketHolder;
friend class FifoTicketHolder;
public:
Ticket(Ticket&& t) : _valid(t._valid) {
t._valid = false;
}
Ticket& operator=(Ticket&& t) {
invariant(!_valid);
_valid = t._valid;
t._valid = false;
return *this;
};
~Ticket() {
// A Ticket can't be destroyed unless it's been released.
invariant(!_valid);
}
/**
* Returns whether or not a ticket is held. The default constructor creates an invalid Ticket
* and the move operators mark the source object as invalid.
*/
bool valid() {
return _valid;
}
private:
Ticket() : _valid(true) {}
void release() {
invariant(_valid);
_valid = false;
}
// No copy constructors.
Ticket(const Ticket&) = delete;
Ticket& operator=(const Ticket&) = delete;
// Whether this represents a ticket being held.
bool _valid;
};
} // namespace mongo
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