ExecutorService,另一种服务，线程

http://heipark.iteye.com/blog/1393847

Executors.newFixedThreadPool和ArrayBlockingQueue一点使用心得          

博客分类：
• Java

 

newFixedThreadPool使用范例：

import java.io.IOException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Test {

    public static void main(String[] args) throws IOException, InterruptedException {
        ExecutorService service = Executors.newFixedThreadPool(2);
        for (int i = 0; i < 6; i++) {
            final int index = i;
            System.out.println("task: " + (i+1));
            Runnable run = new Runnable() {
                @Override
                public void run() {
                    System.out.println("thread start" + index);
                    try {
                        Thread.sleep(Long.MAX_VALUE);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println("thread end" + index);
                }
            };
            service.execute(run);
        }
    }
}

import java.io.IOException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Test {

	public static void main(String[] args) throws IOException, InterruptedException {
		ExecutorService service = Executors.newFixedThreadPool(2);
		for (int i = 0; i < 6; i++) {
			final int index = i;
			System.out.println("task: " + (i+1));
			Runnable run = new Runnable() {
				@Override
				public void run() {
					System.out.println("thread start" + index);
					try {
						Thread.sleep(Long.MAX_VALUE);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					System.out.println("thread end" + index);
				}
			};
			service.execute(run);
		}
	}
}

 输出：

task: 1
task: 2
thread start0
task: 3
task: 4
task: 5
task: 6
task: 7
thread start1
task: 8
task: 9
task: 10
task: 11
task: 12
task: 13
task: 14
task: 15

    从实例可以看到for循环并没有被固定的线程池阻塞住，也就是说所有的线程task都被提交到了ExecutorService中，查看 Executors.newFixedThreadPool()如下：

public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
    }

    可以看到task被提交都了LinkedBlockingQueue中。这里有个问题，如果任务列表很大，一定会把内存撑爆，如何解决？看下面：

import java.io.IOException;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class Test {

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

        BlockingQueue<Runnable> queue = new ArrayBlockingQueue<Runnable>(3);

        ThreadPoolExecutor executor = new ThreadPoolExecutor(3, 3, 1, TimeUnit.HOURS, queue, new ThreadPoolExecutor.CallerRunsPolicy());

        for (int i = 0; i < 10; i++) {
            final int index = i;
            System.out.println("task: " + (index+1));
            Runnable run = new Runnable() {
                @Override
                public void run() {
                    System.out.println("thread start" + (index+1));
                    try {
                        Thread.sleep(Long.MAX_VALUE);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println("thread end" + (index+1));
                }
            };
            executor.execute(run);
        }
    }
}

import java.io.IOException;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class Test {

	public static void main(String[] args) throws IOException, InterruptedException {
		
		BlockingQueue<Runnable> queue = new ArrayBlockingQueue<Runnable>(3);
		
		ThreadPoolExecutor executor = new ThreadPoolExecutor(3, 3, 1, TimeUnit.HOURS, queue, new ThreadPoolExecutor.CallerRunsPolicy());
		
		for (int i = 0; i < 10; i++) {
			final int index = i;
			System.out.println("task: " + (index+1));
			Runnable run = new Runnable() {
				@Override
				public void run() {
					System.out.println("thread start" + (index+1));
					try {
						Thread.sleep(Long.MAX_VALUE);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					System.out.println("thread end" + (index+1));
				}
			};
			executor.execute(run);
		}
	}
}

 输出：

task: 1
task: 2
thread start1
task: 3
task: 4
task: 5
task: 6
task: 7
thread start2
thread start7
thread start6

    线程池最大值为4（？？这里我不明白为什么是设置值+1，即3+1，而不是3），准备执行的任务队列为3。可以看到for循环先处理4个task，然后把3个放到队列。这样就实现了自动阻塞队列的效果。记得要使用ArrayBlockingQueue这个队列，然后设置容量就OK了。

--heipark