Java 线程池预热(Warm-up)实战

import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicBoolean;

public class ThreadPoolWarmUpDemo {

    public static void main(String[] args) throws Exception {
        System.out.println("========== 未开启预热，测试开始 ==========");
        testWithoutWarmUp();

        System.out.println("\n========== 开启预热后，测试开始 ==========");
        testWithWarmUp();
    }

    /** 用于模拟“第一次慢，后面快” */
    private static final AtomicBoolean firstRun = new AtomicBoolean(true);

    /** 模拟核心业务逻辑 */
    private static void mockBizWork() {
        try {
            if (firstRun.compareAndSet(true, false)) {
                // 只在第一次执行时慢
                Thread.sleep(50);
            } else {
                // 后续任务很快
                Thread.sleep(2);
            }
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }

    /** 创建一个全新的线程池（关键） */
    private static ThreadPoolExecutor newExecutor() {
        return new ThreadPoolExecutor(
                4, 4,
                60, TimeUnit.SECONDS,
                new LinkedBlockingQueue<>()
        );
    }

    /** 未开启线程池预热 */
    public static void testWithoutWarmUp() throws Exception {
        ThreadPoolExecutor executor = newExecutor();
        firstRun.set(true);

        long start = System.currentTimeMillis();

        Future<Long> future = executor.submit(() -> {
            long s = System.currentTimeMillis();
            mockBizWork();
            return System.currentTimeMillis() - s;
        });

        long firstCost = future.get();
        long totalCost = System.currentTimeMillis() - start;

        System.out.println("第一次任务耗时 = " + firstCost + " ms");
        System.out.println("整体耗时（含线程创建）= " + totalCost + " ms");

        executor.shutdown();
    }

    /** 开启预热 */
    public static void testWithWarmUp() throws Exception {
        ThreadPoolExecutor executor = newExecutor();
        firstRun.set(true);

        System.out.println(">>> 开始预热核心线程...");
        executor.prestartAllCoreThreads();

        // 预热任务：吃掉“第一次慢”
        for (int i = 0; i < 4; i++) {
            executor.submit(ThreadPoolWarmUpDemo::mockBizWork).get();
        }

        System.out.println(">>> 预热完成！");

        long start = System.currentTimeMillis();

        Future<Long> future = executor.submit(() -> {
            long s = System.currentTimeMillis();
            mockBizWork();
            return System.currentTimeMillis() - s;
        });

        long cost = future.get();
        long totalCost = System.currentTimeMillis() - start;

        System.out.println("第一次任务耗时（已预热）= " + cost + " ms");
        System.out.println("整体耗时（线程已就绪）= " + totalCost + " ms");

        executor.shutdown();
    }
}

executor.prestartAllCoreThreads();
executor.submit(warmTask);