io.questdb.griffin.engine.PerWorkerLocks Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of questdb Show documentation
QuestDB is high performance SQL time series database
There is a newer version: 8.3.2
/*******************************************************************************
 *     ___                  _   ____  ____
 *    / _ \ _   _  ___  ___| |_|  _ \| __ )
 *   | | | | | | |/ _ \/ __| __| | | |  _ \
 *   | |_| | |_| |  __/\__ \ |_| |_| | |_) |
 *    \__\_\\__,_|\___||___/\__|____/|____/
 *
 *  Copyright (c) 2014-2019 Appsicle
 *  Copyright (c) 2019-2024 QuestDB
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 ******************************************************************************/

package io.questdb.griffin.engine;

import io.questdb.cairo.CairoConfiguration;
import io.questdb.cairo.CairoException;
import io.questdb.cairo.sql.ExecutionCircuitBreaker;
import io.questdb.cairo.sql.SqlExecutionCircuitBreaker;
import io.questdb.std.Os;
import io.questdb.std.Rnd;
import org.jetbrains.annotations.NotNull;

import java.util.concurrent.atomic.AtomicIntegerArray;

/**
 * Used to synchronize access to list-like collections used by worker threads.
 */
public class PerWorkerLocks {
    private final AtomicIntegerArray locks;
    // Used to randomize acquire attempts for work stealing threads. Accessed in a racy way, intentionally.
    private final Rnd rnd;
    private final int workerCount;

    public PerWorkerLocks(@NotNull CairoConfiguration configuration, int workerCount) {
        this.rnd = new Rnd(
                configuration.getNanosecondClock().getTicks(),
                configuration.getMicrosecondClock().getTicks()
        );
        this.workerCount = workerCount;
        locks = new AtomicIntegerArray(workerCount);
    }

    public int acquireSlot(int workerId, SqlExecutionCircuitBreaker sqlCircuitBreaker) {
        workerId = workerId == -1 ? rnd.nextInt(workerCount) : workerId;
        while (true) {
            for (int i = 0; i < workerCount; i++) {
                int id = (i + workerId) % workerCount;
                if (locks.compareAndSet(id, 0, 1)) {
                    return id;
                }
            }
            sqlCircuitBreaker.statefulThrowExceptionIfTripped();
            Os.pause();
        }
    }

    public int acquireSlot(int workerId, ExecutionCircuitBreaker circuitBreaker) {
        workerId = workerId == -1 ? rnd.nextInt(workerCount) : workerId;
        while (!circuitBreaker.checkIfTripped()) {
            for (int i = 0; i < workerCount; i++) {
                int id = (i + workerId) % workerCount;
                if (locks.compareAndSet(id, 0, 1)) {
                    return id;
                }
            }
            Os.pause();
        }
        throw CairoException.nonCritical().put("query aborted").setInterruption(true);
    }

    public void releaseSlot(int slot) {
        if (slot > -1) {
            locks.set(slot, 0);
        }
    }
}