Java:使用Executors建立和管理線程

1. 類 Executors

此類中提供的一些方法有：

1.1 public static ExecutorService newCachedThreadPool()

建立一個可根據須要建立新線程的線程池，可是在之前構造的線程可用時將重用它們。對於執行不少短時間異步任務的程序而言，這些線程池一般可提升程序性能。

 

1.2 public static ExecutorService newFixedThreadPool(int nThreads)

建立一個可重用固定線程數的線程池，以共享的×××隊列方式來運行這些線程。

 

1.3 public static ExecutorService newSingleThreadExecutor()

建立一個使用單個 worker 線程的 Executor ，以×××隊列方式來運行該線程。

 

這三個方法均可以配合接口 ThreadFactory 的實例一塊兒使用。而且返回一個 ExecutorService 接口的實例。

2. 接口 ThreadFactory

根據須要建立新線程的對象。使用線程工廠就無需再手工編寫對 new Thread 的調用了，從而容許應用程序使用特殊的線程子類、屬性等等。

此接口最簡單的實現就是：

class SimpleThreadFactory implements ThreadFactory {    public Thread newThread(Runnable r) {      return new Thread(r);    }  }

3. 接口 ExecutorService

該接口提供了管理終止的方法。

4. 建立標準線程池啓動線程

4.1 提供一個簡單的實現 Runnable 接口的線程

MyThread.java

package com.zj.concurrency.executors;   public class MyThread implements Runnable {     private int count = 1, number ;       public MyThread( int num) {        number = num;        System. out .println( "Create Thread-" + number );     }       public void run() {        while ( true ) {            System. out .println( "Thread-" + number + " run " + count + " time(s)" );            if (++ count == 3)               return ;        }     } }

這個線程會打印出相應的建立和執行信息。

 

4.2 使用 CachedThreadPool 啓動線程

CachedThreadPool.java

package com.zj.concurrency.executors; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors;   public class CachedThreadPool {     public static void main(String[] args) {        ExecutorService exec = Executors.newCachedThreadPool();        for ( int i = 0; i < 5; i++)            exec.execute( new MyThread(i));        exec.shutdown();     } }

結果：

Create Thread-0

Create Thread-1

Create Thread-2

Create Thread-3

Thread-0 run 1 time(s)

Thread-0 run 2 time(s)

Thread-1 run 1 time(s)

Thread-1 run 2 time(s)

Thread-2 run 1 time(s)

Thread-2 run 2 time(s)

Create Thread-4

Thread-4 run 1 time(s)

Thread-4 run 2 time(s)

Thread-3 run 1 time(s)

Thread-3 run 2 time(s)

 

4.3 使用 FixedThreadPool 啓動線程

FixedThreadPool.java

package com.zj.concurrency.executors; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors;   public class FixedThreadPool {     public static void main(String[] args) {        ExecutorService exec = Executors.newFixedThreadPool(2);        for ( int i = 0; i < 5; i++)            exec.execute( new MyThread(i));        exec.shutdown();     } }

結果：

Create Thread-0

Create Thread-1

Create Thread-2

Create Thread-3

Create Thread-4

Thread-0 run 1 time(s)

Thread-0 run 2 time(s)

Thread-2 run 1 time(s)

Thread-2 run 2 time(s)

Thread-3 run 1 time(s)

Thread-3 run 2 time(s)

Thread-4 run 1 time(s)

Thread-4 run 2 time(s)

Thread-1 run 1 time(s)

Thread-1 run 2 time(s)

 

4.4 使用 SingleThreadExecutor 啓動線程

SingleThreadExecutor.java

package com.zj.concurrency.executors; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors;   public class SingleThreadExecutor {     public static void main(String[] args) {        ExecutorService exec = Executors.newSingleThreadExecutor();        for ( int i = 0; i < 5; i++)            exec.execute( new MyThread(i));        exec.shutdown();     } }

結果：

Create Thread-0

Create Thread-1

Create Thread-2

Create Thread-3

Create Thread-4

Thread-0 run 1 time(s)

Thread-0 run 2 time(s)

Thread-1 run 1 time(s)

Thread-1 run 2 time(s)

Thread-2 run 1 time(s)

Thread-2 run 2 time(s)

Thread-3 run 1 time(s)

Thread-3 run 2 time(s)

Thread-4 run 1 time(s)

Thread-4 run 2 time(s)

5. 配合 ThreadFactory 接口的使用

咱們試圖給線程加入 daemon 和 priority 的屬性設置。

5.1 設置後臺線程屬性

DaemonThreadFactory.java

package com.zj.concurrency.executors.factory; import java.util.concurrent.ThreadFactory;   public class DaemonThreadFactory implements ThreadFactory {     public Thread newThread(Runnable r) {        Thread t = new Thread(r);        t.setDaemon( true );        return t;     } }

 

5.2 設置優先級屬性

最高優先級 MaxPriorityThreadFactory.java

package com.zj.concurrency.executors.factory; import java.util.concurrent.ThreadFactory;   public class MaxPriorityThreadFactory implements ThreadFactory {     public Thread newThread(Runnable r) {        Thread t = new Thread(r);        t.setPriority(Thread. MAX_PRIORITY );        return t;     } }

最低優先級 MinPriorityThreadFactory.java

package com.zj.concurrency.executors.factory; import java.util.concurrent.ThreadFactory;   public class MinPriorityThreadFactory implements ThreadFactory {     public Thread newThread(Runnable r) {        Thread t = new Thread(r);        t.setPriority(Thread. MIN_PRIORITY );        return t;     } }

 

5.3 啓動帶有屬性設置的線程

ExecFromFactory.java

package com.zj.concurrency.executors; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import com.zj.concurrency.executors.factory.DaemonThreadFactory; import com.zj.concurrency.executors.factory.MaxPriorityThreadFactory; import com.zj.concurrency.executors.factory.MinPriorityThreadFactory;   public class ExecFromFactory {     public static void main(String[] args) throws Exception {        ExecutorService defaultExec = Executors.newCachedThreadPool();        ExecutorService daemonExec = Executors               .newCachedThreadPool( new DaemonThreadFactory());        ExecutorService maxPriorityExec = Executors               .newCachedThreadPool( new MaxPriorityThreadFactory());        ExecutorService minPriorityExec = Executors               .newCachedThreadPool( new MinPriorityThreadFactory());        for ( int i = 0; i < 10; i++)            daemonExec.execute( new MyThread(i));        for ( int i = 10; i < 20; i++)            if (i == 10)               maxPriorityExec.execute( new MyThread(i));            else if (i == 11)               minPriorityExec. execute(new MyThread(i));            else               defaultExec.execute( new MyThread(i));     } }

結果：

Create Thread-0

Create Thread-1

Create Thread-2

Create Thread-3

Thread-0 run 1 time(s)

Thread-0 run 2 time(s)

Thread-1 run 1 time(s)

Thread-1 run 2 time(s)

Thread-2 run 1 time(s)

Thread-2 run 2 time(s)

Create Thread-4

Thread-4 run 1 time(s)

Thread-4 run 2 time(s)

Create Thread-5

Thread-5 run 1 time(s)

Thread-5 run 2 time(s)

Create Thread-6

Create Thread-7

Thread-7 run 1 time(s)

Thread-7 run 2 time(s)

Create Thread-8

Thread-8 run 1 time(s)

Thread-8 run 2 time(s)

Create Thread-9

Create Thread-10

Thread-10 run 1 time(s)

Thread-10 run 2 time(s)

Create Thread-11

Thread-9 run 1 time(s)

Thread-9 run 2 time(s)

Thread-6 run 1 time(s)

Thread-6 run 2 time(s)

Thread-3 run 1 time(s)

Thread-3 run 2 time(s)

Create Thread-12

Create Thread-13

Create Thread-14

Thread-12 run 1 time(s)

Thread-12 run 2 time(s)

Thread-13 run 1 time(s)

Thread-13 run 2 time(s)

Create Thread-15

Thread-15 run 1 time(s)

Thread-15 run 2 time(s)

Create Thread-16

Thread-16 run 1 time(s)

Thread-16 run 2 time(s)

Create Thread-17

Create Thread-18

Create Thread-19

Thread-14 run 1 time(s)

Thread-14 run 2 time(s)

Thread-17 run 1 time(s)

Thread-17 run 2 time(s)

Thread-18 run 1 time(s)

Thread-18 run 2 time(s)

Thread-19 run 1 time(s)

Thread-19 run 2 time(s)

Thread-11 run 1 time(s)

Thread-11 run 2 time(s)