포화 소스 코드 분석 전략

머리말

Github에서 : https://github.com/yihonglei/thinking-in-concurrent

전략 중단

새 작업 제출은 예외가 호출자에 의해 캡처 될 때 기본 정책, 직접 던져 RejectedExecutionException을 선택하지.

new ThreadPoolExecutor.AbortPolicy()

/**
 * A handler for rejected tasks that throws a
 * {@code RejectedExecutionException}.
 */
public static class AbortPolicy implements RejectedExecutionHandler {
    /**
     * Creates an {@code AbortPolicy}.
     */
    public AbortPolicy() { }

    /**
     * Always throws RejectedExecutionException.
     *
     * @param r the runnable task requested to be executed
     * @param e the executor attempting to execute this task
     * @throws RejectedExecutionException always
     */
    public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
        throw new RejectedExecutionException("Task " + r.toString() +
                                             " rejected from " +
                                             e.toString());
    }
}

두 CallerRuns 전략

작업이 슬로우되지 않는 포기하지만, 일부 작업은 호출자에게 떨어질 것이다하지 메커니즘을 조정합니다. 그것은 스레드 풀의 스레드에서 새 작업을 수행하지 않습니다

그러나 구현을 담당하는 새 작업 호출 exector 스레드입니다 튜닝을 실행합니다.

new ThreadPoolExecutor.CallerRunsPolicy()

/**
 * A handler for rejected tasks that runs the rejected task
 * directly in the calling thread of the {@code execute} method,
 * unless the executor has been shut down, in which case the task
 * is discarded.
 */
public static class CallerRunsPolicy implements RejectedExecutionHandler {
    /**
     * Creates a {@code CallerRunsPolicy}.
     */
    public CallerRunsPolicy() { }

    /**
     * Executes task r in the caller's thread, unless the executor
     * has been shut down, in which case the task is discarded.
     *
     * @param r the runnable task requested to be executed
     * @param e the executor attempting to execute this task
     */
    public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
        if (!e.isShutdown()) {
            r.run();
        }
    }
}

세 가지 전략을 폐기

새 작업 제출은 포기되었다.

new ThreadPoolExecutor.DiscardPolicy()

/**
 * A handler for rejected tasks that silently discards the
 * rejected task.
 */
public static class DiscardPolicy implements RejectedExecutionHandler {
    /**
     * Creates a {@code DiscardPolicy}.
     */
    public DiscardPolicy() { }

    /**
     * Does nothing, which has the effect of discarding task r.
     *
     * @param r the runnable task requested to be executed
     * @param e the executor attempting to execute this task
     */
    public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
    }
}

네 DiscardOldest 전략

큐 작업은 "팀의 머리"입니다, 다음 새 작업을 제출하려고합니다. 작업 헤드 (작업 큐 우선 순위 큐 현장에 적합하지 않음) 삭제됩니다

new ThreadPoolExecutor.DiscardOldestPolicy()

/**
 * A handler for rejected tasks that discards the oldest unhandled
 * request and then retries {@code execute}, unless the executor
 * is shut down, in which case the task is discarded.
 */
public static class DiscardOldestPolicy implements RejectedExecutionHandler {
    /**
     * Creates a {@code DiscardOldestPolicy} for the given executor.
     */
    public DiscardOldestPolicy() { }

    /**
     * Obtains and ignores the next task that the executor
     * would otherwise execute, if one is immediately available,
     * and then retries execution of task r, unless the executor
     * is shut down, in which case task r is instead discarded.
     *
     * @param r the runnable task requested to be executed
     * @param e the executor attempting to execute this task
     */
    public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
        if (!e.isShutdown()) {
            e.getQueue().poll();
            e.execute(r);
        }
    }
}

다섯 사용자 정의 포화 처리 전략

import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.ThreadPoolExecutor;
/**
 * 循环处理,当队列有空位时,该任务进入队列，等待线程池处理
 */
public class CustomRejectedExecutionHandler implements RejectedExecutionHandler {
  public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
    try {
      executor.getQueue().put(r);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}