线程池处理流程分析

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上述是线程池处理任务的流程，相信大家都在网上搜到不少，今天咱们来用代码验证一下，亲自看看这个流程是不是这样的

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.common.util.concurrent.ThreadFactoryBuilder;
import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.*;


@Slf4j
public class Test {

    private static ExecutorService service;
    public static ObjectMapper objectMapper = new ObjectMapper();

    static {
        ThreadFactory threadFactory = new ThreadFactoryBuilder().setNameFormat("demo-pool-%d").build();
        //核心线程2个，最大线程4个，存活时间20秒，队列最大长度为2，
        service = new ThreadPoolExecutor(2, 4, 20, TimeUnit.SECONDS, new ArrayBlockingQueue<>(2), threadFactory);
    }

    public static void main(String[] args) throws JsonProcessingException, InterruptedException {

        for (int i = 0; i < 5; i++) {
            //每次等待50毫秒，确保前一个任务可以提交
            TimeUnit.MILLISECONDS.sleep(50);
            int finalI = i;
            service.execute(() -> {
                try {
                    //打印当前执行任务的线程名字和任务id
                    log.info(finalI + "-----" + Thread.currentThread().getName() + "-------before");
                    TimeUnit.SECONDS.sleep(10);
                    log.info(finalI + "-----" + Thread.currentThread().getName() + "-------after");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            });
        }
    }
}

上述代码打印结果如下：

2020-10-30 22:07:36.051 INFO [demo-pool-0]com.tomorrowsg.test.test.Test.lambda0:40 -0-----demo-pool-0-------before
2020-10-30 22:07:36.100 INFO [demo-pool-1]com.tomorrowsg.test.test.Test.lambda0:40 -1-----demo-pool-1-------before
2020-10-30 22:07:36.252 INFO [demo-pool-2]com.tomorrowsg.test.test.Test.lambda0:40 -4-----demo-pool-2-------before
2020-10-30 22:07:46.055 INFO [demo-pool-0]com.tomorrowsg.test.test.Test.lambda0:42 -0-----demo-pool-0-------after
2020-10-30 22:07:46.056 INFO [demo-pool-0]com.tomorrowsg.test.test.Test.lambda0:40 -2-----demo-pool-0-------before
2020-10-30 22:07:46.101 INFO [demo-pool-1]com.tomorrowsg.test.test.Test.lambda0:42 -1-----demo-pool-1-------after
2020-10-30 22:07:46.101 INFO [demo-pool-1]com.tomorrowsg.test.test.Test.lambda0:40 -3-----demo-pool-1-------before
2020-10-30 22:07:46.252 INFO [demo-pool-2]com.tomorrowsg.test.test.Test.lambda0:42 -4-----demo-pool-2-------after
2020-10-30 22:07:56.058 INFO [demo-pool-0]com.tomorrowsg.test.test.Test.lambda0:42 -2-----demo-pool-0-------after
2020-10-30 22:07:56.102 INFO [demo-pool-1]com.tomorrowsg.test.test.Test.lambda0:42 -3-----demo-pool-1-------after

从上面可以看出，
线程池两个核心线程（demo-pool-0、demo-pool-1）先执行0、1两个任务，然后将2、3两个任务添加到队列中，由于队列满了，所以又创建了一个非核心线程（demo-pool-2）处理任务4，等两个核心线程执行结束后又执行任务2和3。