Java线程池创建简单理解
发布者 : 管理员-Adler | 发布时间 : 2019-01-17 19:16:36文章号 : 21 | 阅读量 : 5+1 | AAW值(?) : 0.00 (仅供参考)
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class cachethreadpool {
public static void main (String[] args) {
ExecutorService es = Executors.newFixedThreadPool(3);
int setup = 1;
for (int i = 0; i < setup; i++) { //for循环开始
final int index = i;
setup++;
es.execute(new Runnable() {
@Override
public void run() {
try {
System.out.println(index);
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
} //for循环结束
}
}
(个人理解)步骤:
1. //新建ExecutorService(线程池)
ExecutorService es = new Executors.newFixedThreadPool(3); //线程池大小为3,所以创建三个线程
2. //用ExecutorService的execute方法执行线程池中的线程
es.execute(new Runnable() { //新建Runnable
@Override
public void run() { //重写run方法(Runnable)
try{
System.out.println(index);
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});//好像还挺简单的…
深入理解
import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class cachethreadpool { public static void main (String[] args) { ExecutorService es = Executors.newFixedThreadPool(3); Prints pts = new Prints(1); while (true) { es.execute(pts); } /*Prints pts = new Prints(1); pts.run();*/ } } class Prints implements Runnable { int thnum; public Prints(int thnum) { this.thnum = thnum; } public void run() { Long time; Long time2; Long time3; time = System.currentTimeMillis(); for (int i = 0; i < 20; i++) { try { System.out.println("线程" + thnum + " NO." + i); Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } time2 = System.currentTimeMillis(); time3 = time2 - time; System.out.println(time3); } }
注意:给es.execute加了一个for循环,实际上在执行
ExecutorService es = Executors.newFixedThreadPool(3);
的时候,es就已经开始多线程线程了,而execute实际上可以指定执行很多个Runnable任务(class),只有一个限制,就是一个周期只能运行3个。
修改一下代码,再次运行尝试:
import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class cachethreadpool { public static void main (String[] args) { ExecutorService es = Executors.newFixedThreadPool(3); Prints pts = new Prints(1); Prints2 pts2 = new Prints2(2); while (true) { es.execute(pts); es.execute(pts2); } /*Prints pts = new Prints(1); pts.run();*/ } } class Prints implements Runnable { int thnum; public Prints(int thnum) { this.thnum = thnum; } public void run() { Long time; Long time2; Long time3; time = System.currentTimeMillis(); for (int i = 0; i < 20; i++) { try { System.out.println("线程" + thnum + " NO." + i); Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } time2 = System.currentTimeMillis(); time3 = time2 - time; System.out.println(time3); } } class Prints2 implements Runnable { int thnum; public Prints2(int thnum) { this.thnum = thnum; } public void run() { Long time; Long time2; Long time3; time = System.currentTimeMillis(); for (int i = 0; i < 20; i++) { try { System.out.println("线程" + thnum + " NO." + i); Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } time2 = System.currentTimeMillis(); time3 = time2 - time; System.out.println(time3); } }
运行结果:
线程2 NO.0
线程1 NO.0
线程1 NO.0
线程1 NO.1
线程1 NO.1
线程2 NO.1
线程1 NO.2
线程2 NO.2
线程1 NO.2
线程1 NO.3
线程1 NO.3
线程2 NO.3
注意:运行结果每1秒会出现3个(因为有个sleep),而按照什么顺序执行实际上是看pts和pts2两个线程哪个先抢到cpu的资源。
其它线程池…
Java通过Executors提供四种线程池,分别为:
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。弹性线程池,无上限线程数(但要小心因为线程太多而导致的崩溃)
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。 推荐,一次只能运行特定数量的线程
newScheduledThreadPool 创建一个定长线程池,支持定时及周期性任务执行。
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,保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行。