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/**
* Copyright (C) 2021-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.
*/
#include "mongo/db/allocate_cursor_id.h"
#include "mongo/util/assert_util.h"
namespace mongo::generic_cursor {
CursorId allocateCursorId(const std::function<bool(CursorId)>& pred, PseudoRandom& random) {
for (int i = 0; i < 10000; i++) {
CursorId id = random.nextInt64();
// A cursor id of zero is reserved to indicate that the cursor has been closed. If the
// random number generator gives us zero, then try again.
if (id == 0) {
continue;
}
// Avoid negative cursor ids by taking the absolute value. If the cursor id is the minimum
// representable negative number, then just generate another random id.
if (id == std::numeric_limits<CursorId>::min()) {
continue;
}
id = std::abs(id);
if (pred(id)) {
// The cursor id is not already in use, so return it.
return id;
}
// The cursor id is already in use. Generate another random id.
}
// We failed to generate a unique cursor id.
fassertFailed(17360);
}
} // namespace mongo::generic_cursor
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