Java 四种线程池的使用
通过Executors提供四中线程池,分别如下
newCachedThreadPool:创建一个可缓存线程池,若线程长度超过处理需要,可灵活回收空闲线程,若无可回收线程,则新建线程;
newFixedThreadPool:创建一个定长线程池,可控制线程最大并发数,超出的线程会在队列中等待;
newScheduledThreadPool:创建一个定长线程池,定时及支持周期执行任务;
newSingleThreadExecutor:创建一个单例化线程池,他会用唯一工作线程来执行任务,保证任务按照指定顺序(FIFO,LIFO优先级)来执行
1)newCachedThreadpool
线程池为无限大,当执行第二个任务时第一个已完成,会重复使用执行第一个任务的线程,而不用每次新建一个线程
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); } }); } } }
2)newFixedThreadPool
因为线程池大小为3,每个任务输出index后sleep2s,所以每2s打印3个数字
定长线程池的大小最好根据系统资源进行设置,如Runtime.getRuntime().availableProcessors()
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(); } } }); } } }
3)newScheduledThreadPool
延迟3s执行
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); } }
定期执行示例,---延迟1s后每3s执行一次
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); } }
4)newSingleThreadExecutor;
结果依次输出,相当于各执行各的任务,
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(); } } }); } } }