Think_in_java_4th（并发学习二）

使用Executor

java.util.concurrent

CachedThreadPool

package concurrency.ExecutorService;

//: concurrency/CachedThreadPool.java
import java.util.concurrent.*;

import concurrency.LiftOff.LiftOff;

public class CachedThreadPool {
    public static void main(String[] args) {
        ExecutorService exec = Executors.newCachedThreadPool();
        for (int i = 0; i < 5; i++)
            exec.execute(new LiftOff());
        exec.shutdown();
    }
} /*
   * Output: (Sample) #0(9), #0(8), #1(9), #2(9), #3(9), #4(9), #0(7), #1(8),
   * #2(8), #3(8), #4(8), #0(6), #1(7), #2(7), #3(7), #4(7), #0(5), #1(6), #2(6),
   * #3(6), #4(6), #0(4), #1(5), #2(5), #3(5), #4(5), #0(3), #1(4), #2(4), #3(4),
   * #4(4), #0(2), #1(3), #2(3), #3(3), #4(3), #0(1), #1(2), #2(2), #3(2), #4(2),
   * #0(Liftoff!), #1(1), #2(1), #3(1), #4(1), #1(Liftoff!), #2(Liftoff!),
   * #3(Liftoff!), #4(Liftoff!),
   */// :~

    /**
     * Creates a thread pool that creates new threads as needed, but
     * will reuse previously constructed threads when they are
     * available.  These pools will typically improve the performance
     * of programs that execute many short-lived asynchronous tasks.
     * Calls to {@code execute} will reuse previously constructed
     * threads if available. If no existing thread is available, a new
     * thread will be created and added to the pool. Threads that have
     * not been used for sixty seconds are terminated and removed from
     * the cache. Thus, a pool that remains idle for long enough will
     * not consume any resources. Note that pools with similar
     * properties but different details (for example, timeout parameters)
     * may be created using {@link ThreadPoolExecutor} constructors.
     *
     * @return the newly created thread pool
     */
    public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
    }

以上，JDK里头关于Executors.newCachedThreadPool的定义。

通过创建线程池，去管理线程。并且，线程池通过exec.execute去启动新的线程。

newCachedThreadPool会为每一个任务创建一个线程。

FixedThreadPool

package concurrency.ExecutorService;

//: concurrency/FixedThreadPool.java
import java.util.concurrent.*;

import concurrency.LiftOff.LiftOff;

public class FixedThreadPool {
    public static void main(String[] args) {
        // Constructor argument is number of threads:
        ExecutorService exec = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 5; i++)
            exec.execute(new LiftOff());
        exec.shutdown();
    }
} /*
   * Output: (Sample) #0(9), #0(8), #1(9), #2(9), #3(9), #4(9), #0(7), #1(8),
   * #2(8), #3(8), #4(8), #0(6), #1(7), #2(7), #3(7), #4(7), #0(5), #1(6), #2(6),
   * #3(6), #4(6), #0(4), #1(5), #2(5), #3(5), #4(5), #0(3), #1(4), #2(4), #3(4),
   * #4(4), #0(2), #1(3), #2(3), #3(3), #4(3), #0(1), #1(2), #2(2), #3(2), #4(2),
   * #0(Liftoff!), #1(1), #2(1), #3(1), #4(1), #1(Liftoff!), #2(Liftoff!),
   * #3(Liftoff!), #4(Liftoff!),
   */// :~

newFixedThreadPool会创建指定个数的线程。

SingleThreadExecutor

package concurrency.ExecutorService;

//: concurrency/SingleThreadExecutor.java
import java.util.concurrent.*;

import concurrency.LiftOff.LiftOff;

public class SingleThreadExecutor {
    public static void main(String[] args) {
        ExecutorService exec = Executors.newSingleThreadExecutor();
        for (int i = 0; i < 5; i++)
            exec.execute(new LiftOff());
        exec.shutdown();
    }
} /*
   * Output: #0(9), #0(8), #0(7), #0(6), #0(5), #0(4), #0(3), #0(2), #0(1),
   * #0(Liftoff!), #1(9), #1(8), #1(7), #1(6), #1(5), #1(4), #1(3), #1(2), #1(1),
   * #1(Liftoff!), #2(9), #2(8), #2(7), #2(6), #2(5), #2(4), #2(3), #2(2), #2(1),
   * #2(Liftoff!), #3(9), #3(8), #3(7), #3(6), #3(5), #3(4), #3(3), #3(2), #3(1),
   * #3(Liftoff!), #4(9), #4(8), #4(7), #4(6), #4(5), #4(4), #4(3), #4(2), #4(1),
   * #4(Liftoff!),
   */// :~

newSingleThreadExecutor线程数为一的newFixedThreadPool。

参考

Java编程思想(第4版)    656页开始

Thinking in Java（第四版 ）  1120页开始