Java的四种线程池

发表于 | 分类于 |

Java通过Executors提供了四种线程池：

  • newCachedThreadPool创建一个可缓存线程池，如果线程池长度超过处理需要，可灵活回收空闲线程，若无可回收，则新建线程。 
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    package test;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    public class ThreadPoolExecutorTest {
     public static void main(String[] args) {
      ExecutorService cachedThreadPool = Executors.newCachedThreadPool();
      for (int i = 0; i < 10; i++) {
       final int index = i;
       try {
        Thread.sleep(index * 1000);
       } catch (InterruptedException e) {
        e.printStackTrace();
       }
       cachedThreadPool.execute(new Runnable() {
        public void run() {
         System.out.println(index);
        }
       });
      }
     }
    }

线程池为无限大，当执行第二个任务时第一个任务已经完成，会复用执行第一个任务的线程，而不用每次新建线程.

  • newFixedThreadPool创建一个定长线程池，可控制线程最大并发数，超过的线程会在队列中等待。
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    package test;  
    import java.util.concurrent.ExecutorService;  
    import java.util.concurrent.Executors;  
    public class ThreadPoolExecutorTest {  
     public static void main(String[] args) {  
      ExecutorService fixedThreadPool = Executors.newFixedThreadPool(3);  
      for (int i = 0; i < 10; i++) {  
       final int index = i;  
       fixedThreadPool.execute(new Runnable() {  
        public void run() {  
         try {  
          System.out.println(index);  
          Thread.sleep(2000);  
         } catch (InterruptedException e) {  
          e.printStackTrace();  
         }  
        }  
       });  
      }  
     }  
    }

因为线程池大小为3，每个任务输出index后sleep 2秒，所以没两秒打印3个数字。

  • newScheduledThreadPool创建一个定长线程池，支持定时及周期性任务执行。
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    package test;  
    import java.util.concurrent.Executors;  
    import java.util.concurrent.ScheduledExecutorService;  
    import java.util.concurrent.TimeUnit;  
    public class ThreadPoolExecutorTest {  
     public static void main(String[] args) {  
      ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);  
      scheduledThreadPool.schedule(new Runnable() {  
       public void run() {  
        System.out.println("delay 3 seconds");  
       }  
      }, 3, TimeUnit.SECONDS);  
     }  
    }

表示延迟3秒执行。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
package test;  
import java.util.concurrent.Executors;  
import java.util.concurrent.ScheduledExecutorService;  
import java.util.concurrent.TimeUnit;  
public class ThreadPoolExecutorTest {  
 public static void main(String[] args) {  
  ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);  
  scheduledThreadPool.scheduleAtFixedRate(new Runnable() {  
   public void run() {  
    System.out.println("delay 1 seconds, and excute every 3 seconds");  
   }  
  }, 1, 3, TimeUnit.SECONDS);  
 }  
}

表示延迟1秒后每3秒执行一次。

  • newSingleThreadExecutor创建一个单线程化的线程池，它只会用唯一的工作线程来执行任务，保证所有的任务按照指定顺序（FIFO，LIFO,优先级）执行。
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    package test;  
    import java.util.concurrent.ExecutorService;  
    import java.util.concurrent.Executors;  
    public class ThreadPoolExecutorTest {  
     public static void main(String[] args) {  
      ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();  
      for (int i = 0; i < 10; i++) {  
       final int index = i;  
       singleThreadExecutor.execute(new Runnable() {  
        public void run() {  
         try {  
          System.out.println(index);  
          Thread.sleep(2000);  
         } catch (InterruptedException e) {  
          e.printStackTrace();  
         }  
        }  
       });  
      }  
     }  
    }

顺序执行每个任务。