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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/lock_manager_defs.h"
#include "mongo/util/assert_util.h"
namespace mongo {
/**
* Simple intrusive list implementation for the lock's granted and conflicting lists. Does not
* own its contents, just uses the intrusive pointers on the LockRequest structure to link them
* together. Therefore requests must outlive this list.
*
* Intentionally implemented as a POD in order to avoid constructor/destructor invocations.
*
* NOTE: This class should not be used for generic purposes and should not be used outside of
* the Lock Manager library.
*/
class LockRequestList {
public:
void push_front(LockRequest* request) {
// Sanity check that we do not reuse entries without cleaning them up
invariant(request->next == nullptr);
invariant(request->prev == nullptr);
if (_front == nullptr) {
_front = _back = request;
} else {
request->next = _front;
_front->prev = request;
_front = request;
}
}
void push_back(LockRequest* request) {
// Sanity check that we do not reuse entries without cleaning them up
invariant(request->next == nullptr);
invariant(request->prev == nullptr);
if (_front == nullptr) {
_front = _back = request;
} else {
request->prev = _back;
_back->next = request;
_back = request;
}
}
void remove(LockRequest* request) {
if (request->prev != nullptr) {
request->prev->next = request->next;
} else {
_front = request->next;
}
if (request->next != nullptr) {
request->next->prev = request->prev;
} else {
_back = request->prev;
}
request->prev = nullptr;
request->next = nullptr;
}
void reset() {
_front = _back = nullptr;
}
bool empty() const {
return _front == nullptr;
}
// Pointers to the beginning and the end of the list
LockRequest* _front;
LockRequest* _back;
};
} // namespace mongo
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