Java自定义线程池-记录每个线程执行耗时

　　ThreadPoolExecutor是可扩展的，其提供了几个可在子类化中改写的方法，如下：

protected void beforeExecute(Thread t, Runnable r) { }
protected void afterExecute(Runnable r, Throwable t) { }
protected void terminated() { }

　　现基于此，完成一个统计每个线程执行耗时，并计算平均耗时的 自定义线程池样例。通过 beforeExecute、afterExecute、terminated 方法来添加日志记录和统计信息收集。为了测量任务的运行时间，beforeExecute必须记录开始时间并把它保存到一个ThreadLocal变量中，然后由afterExecute来读取。同时，使用两个 AtomicLong变量，分别用以记录已处理的任务数和总的处理时间，并通过terminated来输出包含平均任务时间的日志消息。

　　自定义线程池代码如下：

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import java.util.logging.Logger;

/**
 * 自定义线程池
 */
public class TimingThreadPool extends ThreadPoolExecutor {

    private final ThreadLocal<Long> startTime = new ThreadLocal<>();
    private final Logger log = Logger.getLogger("TimingThreadPool");
    private final AtomicLong numTasks = new AtomicLong();
    private final AtomicLong totalTime = new AtomicLong();

    public TimingThreadPool(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }

    @Override
    protected void beforeExecute(Thread t, Runnable r) {
        super.beforeExecute(t, r);
        log.info(String.format("Thread %s: start %s",t,r));
        startTime.set(System.nanoTime());
    }

    @Override
    protected void afterExecute(Runnable r, Throwable t) {
        try {
            long endTime = System.nanoTime();
            long taskTime = endTime - startTime.get();
            numTasks.incrementAndGet();
            totalTime.addAndGet(taskTime);
            log.info(String.format("Thread %s: end %s, time=%dns",t,r,taskTime));

        } finally {
            super.afterExecute(r,t);
        }
    }

    @Override
    protected void terminated() {
        try {
            log.info(String.format("Terminated: avg time=%dns",totalTime.get() / numTasks.get()));
        } finally {
            super.terminated();
        }
    }
}

　　测试执行效果代码如下：

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;

/**
 * 测试自定义线程池
 */
public class TestCustomThreadPool {

    public static void main(String[] args) {

        try {
            TimingThreadPool threadPool = new TimingThreadPool(,,0L, TimeUnit.MILLISECONDS,
                    new LinkedBlockingQueue<Runnable>());

            List<TestCallable> tasks = new ArrayList<>();

            for (int i =  ; i <  ; i++) {
                tasks.add(new TestCallable());
            }

            List<Future<Long>> futures = threadPool.invokeAll(tasks);
            for (Future<Long> future :
                    futures) {
                System.out.print(" - "+future.get());
            }
            threadPool.shutdown();

        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    static class TestCallable implements Callable<java.lang.Long> {

        @Override
        public Long call() throws Exception {
            long total =  ;
            for (int i =  ; i <  ; i++) {
                long now = getRandom();
                total += now;
            }
            Thread.sleep(total);
            return total;
        }

        public long getRandom () {
            return Math.round(Math.random() * );
        }
    }

}

执行结果：