Java多线程4 初识线程池
2018-11-27 本文已影响20人
香沙小熊
前言
Java为什么引入线程池？
创建线程示例
new Thread(new Runnable() {
@Override
public void run() {
}
}).start();
new Thread的弊端
- 每次new Thread新建对象性能差。
- 线程缺乏统一管理，可能无限制新建线程，相互之间竞争，及可能占用过多系统资源导致死机或oom。
- 缺乏更多功能，如定时执行、定期执行、线程中断。
相比new Thread，Java提供的四种线程池的好处在于：
- 重用存在的线程，减少对象创建、消亡的开销，性能佳。
- 可有效控制最大并发线程数，提高系统资源的使用率，同时避免过多资源竞争，避免堵塞。
- 提供定时执行、定期执行、单线程、并发数控制等功能。
1.Java四种线程池
Java通过Executors提供四种线程池，分别为：
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。
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。
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。
newScheduledThreadPool 创建一个定长线程池，支持定时及周期性任务执行。
1.1 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。
public class ThreadPoolTest {
public static void main(String[] args) {
//固定线程池
ExecutorService threadPool = Executors.newFixedThreadPool(3);
for (int i = 1; i < 10; i++) {
int finalI = i;
threadPool.execute(new Runnable() {
@Override
public void run() {
for (int j = 1; j < 10; j++) {
try {
Thread.sleep(20);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + " is looping of " + j + " for task of " + finalI
);
}
}
});
}
}
}
pool-1-thread-3 is looping of 1 for task of 3
pool-1-thread-2 is looping of 1 for task of 2
pool-1-thread-1 is looping of 1 for task of 1
pool-1-thread-3 is looping of 2 for task of 3
pool-1-thread-1 is looping of 2 for task of 1
pool-1-thread-2 is looping of 2 for task of 2
pool-1-thread-3 is looping of 3 for task of 3
pool-1-thread-1 is looping of 3 for task of 1
pool-1-thread-2 is looping of 3 for task of 2
pool-1-thread-3 is looping of 4 for task of 3
pool-1-thread-2 is looping of 4 for task of 2
pool-1-thread-1 is looping of 4 for task of 1
pool-1-thread-1 is looping of 5 for task of 1
pool-1-thread-2 is looping of 5 for task of 2
pool-1-thread-3 is looping of 5 for task of 3
pool-1-thread-1 is looping of 6 for task of 1
pool-1-thread-3 is looping of 6 for task of 3
pool-1-thread-2 is looping of 6 for task of 2
pool-1-thread-1 is looping of 7 for task of 1
pool-1-thread-3 is looping of 7 for task of 3
pool-1-thread-2 is looping of 7 for task of 2
pool-1-thread-1 is looping of 8 for task of 1
pool-1-thread-3 is looping of 8 for task of 3
pool-1-thread-2 is looping of 8 for task of 2
pool-1-thread-1 is looping of 9 for task of 1
pool-1-thread-2 is looping of 9 for task of 2
pool-1-thread-3 is looping of 9 for task of 3
pool-1-thread-1 is looping of 1 for task of 4
pool-1-thread-2 is looping of 1 for task of 5
pool-1-thread-3 is looping of 1 for task of 6
pool-1-thread-1 is looping of 2 for task of 4
pool-1-thread-2 is looping of 2 for task of 5
pool-1-thread-3 is looping of 2 for task of 6
pool-1-thread-1 is looping of 3 for task of 4
pool-1-thread-2 is looping of 3 for task of 5
pool-1-thread-3 is looping of 3 for task of 6
pool-1-thread-3 is looping of 4 for task of 6
pool-1-thread-1 is looping of 4 for task of 4
pool-1-thread-2 is looping of 4 for task of 5
pool-1-thread-3 is looping of 5 for task of 6
pool-1-thread-1 is looping of 5 for task of 4
pool-1-thread-2 is looping of 5 for task of 5
pool-1-thread-2 is looping of 6 for task of 5
pool-1-thread-1 is looping of 6 for task of 4
pool-1-thread-3 is looping of 6 for task of 6
pool-1-thread-2 is looping of 7 for task of 5
pool-1-thread-3 is looping of 7 for task of 6
pool-1-thread-1 is looping of 7 for task of 4
pool-1-thread-1 is looping of 8 for task of 4
pool-1-thread-3 is looping of 8 for task of 6
pool-1-thread-2 is looping of 8 for task of 5
pool-1-thread-3 is looping of 9 for task of 6
pool-1-thread-2 is looping of 9 for task of 5
pool-1-thread-1 is looping of 9 for task of 4
pool-1-thread-2 is looping of 1 for task of 8
pool-1-thread-1 is looping of 1 for task of 9
pool-1-thread-3 is looping of 1 for task of 7
pool-1-thread-1 is looping of 2 for task of 9
pool-1-thread-2 is looping of 2 for task of 8
pool-1-thread-3 is looping of 2 for task of 7
pool-1-thread-1 is looping of 3 for task of 9
pool-1-thread-2 is looping of 3 for task of 8
pool-1-thread-3 is looping of 3 for task of 7
pool-1-thread-1 is looping of 4 for task of 9
pool-1-thread-2 is looping of 4 for task of 8
pool-1-thread-3 is looping of 4 for task of 7
pool-1-thread-2 is looping of 5 for task of 8
pool-1-thread-3 is looping of 5 for task of 7
pool-1-thread-1 is looping of 5 for task of 9
pool-1-thread-2 is looping of 6 for task of 8
pool-1-thread-1 is looping of 6 for task of 9
pool-1-thread-3 is looping of 6 for task of 7
pool-1-thread-3 is looping of 7 for task of 7
pool-1-thread-1 is looping of 7 for task of 9
pool-1-thread-2 is looping of 7 for task of 8
pool-1-thread-3 is looping of 8 for task of 7
pool-1-thread-1 is looping of 8 for task of 9
pool-1-thread-2 is looping of 8 for task of 8
pool-1-thread-3 is looping of 9 for task of 7
pool-1-thread-2 is looping of 9 for task of 8
pool-1-thread-1 is looping of 9 for task of 9
定长线程池的大小最好根据系统资源进行设置。如Runtime.getRuntime().availableProcessors()
1.2 newFixedThreadPool
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。
public class ThreadPoolTest {
public static void main(String[] args) {
//固定线程池
ExecutorService threadPool = Executors.newSingleThreadExecutor();
for (int i = 1; i < 10; i++) {
int finalI = i;
threadPool.execute(new Runnable() {
@Override
public void run() {
for (int j = 1; j < 10; j++) {
try {
Thread.sleep(20);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + " is looping of " + j + " for task of " + finalI
);
}
}
});
}
}
}
pool-1-thread-1 is looping of 1 for task of 1
pool-1-thread-1 is looping of 2 for task of 1
pool-1-thread-1 is looping of 3 for task of 1
pool-1-thread-1 is looping of 4 for task of 1
pool-1-thread-1 is looping of 5 for task of 1
pool-1-thread-1 is looping of 6 for task of 1
pool-1-thread-1 is looping of 7 for task of 1
pool-1-thread-1 is looping of 8 for task of 1
pool-1-thread-1 is looping of 9 for task of 1
pool-1-thread-1 is looping of 1 for task of 2
pool-1-thread-1 is looping of 2 for task of 2
pool-1-thread-1 is looping of 3 for task of 2
pool-1-thread-1 is looping of 4 for task of 2
pool-1-thread-1 is looping of 5 for task of 2
pool-1-thread-1 is looping of 6 for task of 2
pool-1-thread-1 is looping of 7 for task of 2
pool-1-thread-1 is looping of 8 for task of 2
pool-1-thread-1 is looping of 9 for task of 2
pool-1-thread-1 is looping of 1 for task of 3
pool-1-thread-1 is looping of 2 for task of 3
pool-1-thread-1 is looping of 3 for task of 3
pool-1-thread-1 is looping of 4 for task of 3
pool-1-thread-1 is looping of 5 for task of 3
pool-1-thread-1 is looping of 6 for task of 3
pool-1-thread-1 is looping of 7 for task of 3
pool-1-thread-1 is looping of 8 for task of 3
pool-1-thread-1 is looping of 9 for task of 3
pool-1-thread-1 is looping of 1 for task of 4
pool-1-thread-1 is looping of 2 for task of 4
pool-1-thread-1 is looping of 3 for task of 4
pool-1-thread-1 is looping of 4 for task of 4
pool-1-thread-1 is looping of 5 for task of 4
pool-1-thread-1 is looping of 6 for task of 4
pool-1-thread-1 is looping of 7 for task of 4
pool-1-thread-1 is looping of 8 for task of 4
pool-1-thread-1 is looping of 9 for task of 4
pool-1-thread-1 is looping of 1 for task of 5
pool-1-thread-1 is looping of 2 for task of 5
pool-1-thread-1 is looping of 3 for task of 5
pool-1-thread-1 is looping of 4 for task of 5
pool-1-thread-1 is looping of 5 for task of 5
pool-1-thread-1 is looping of 6 for task of 5
pool-1-thread-1 is looping of 7 for task of 5
pool-1-thread-1 is looping of 8 for task of 5
pool-1-thread-1 is looping of 9 for task of 5
pool-1-thread-1 is looping of 1 for task of 6
pool-1-thread-1 is looping of 2 for task of 6
pool-1-thread-1 is looping of 3 for task of 6
pool-1-thread-1 is looping of 4 for task of 6
pool-1-thread-1 is looping of 5 for task of 6
pool-1-thread-1 is looping of 6 for task of 6
pool-1-thread-1 is looping of 7 for task of 6
pool-1-thread-1 is looping of 8 for task of 6
pool-1-thread-1 is looping of 9 for task of 6
pool-1-thread-1 is looping of 1 for task of 7
pool-1-thread-1 is looping of 2 for task of 7
pool-1-thread-1 is looping of 3 for task of 7
pool-1-thread-1 is looping of 4 for task of 7
pool-1-thread-1 is looping of 5 for task of 7
pool-1-thread-1 is looping of 6 for task of 7
pool-1-thread-1 is looping of 7 for task of 7
pool-1-thread-1 is looping of 8 for task of 7
pool-1-thread-1 is looping of 9 for task of 7
pool-1-thread-1 is looping of 1 for task of 8
pool-1-thread-1 is looping of 2 for task of 8
pool-1-thread-1 is looping of 3 for task of 8
pool-1-thread-1 is looping of 4 for task of 8
pool-1-thread-1 is looping of 5 for task of 8
pool-1-thread-1 is looping of 6 for task of 8
pool-1-thread-1 is looping of 7 for task of 8
pool-1-thread-1 is looping of 8 for task of 8
pool-1-thread-1 is looping of 9 for task of 8
pool-1-thread-1 is looping of 1 for task of 9
pool-1-thread-1 is looping of 2 for task of 9
pool-1-thread-1 is looping of 3 for task of 9
pool-1-thread-1 is looping of 4 for task of 9
pool-1-thread-1 is looping of 5 for task of 9
pool-1-thread-1 is looping of 6 for task of 9
pool-1-thread-1 is looping of 7 for task of 9
pool-1-thread-1 is looping of 8 for task of 9
pool-1-thread-1 is looping of 9 for task of 9
结果依次输出，相当于顺序执行各个任务。
现行大多数GUI程序都是单线程的。Android中单线程可用于数据库操作，文件操作，应用批量安装，应用批量删除等不适合并发但可能IO阻塞性及影响UI线程响应的操作。
1.3 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
public class ThreadPoolTest {
public static void main(String[] args) {
//固定线程池
ExecutorService threadPool = Executors.newCachedThreadPool();
for (int i = 1; i < 10; i++) {
int finalI = i;
threadPool.execute(new Runnable() {
@Override
public void run() {
for (int j = 1; j < 10; j++) {
try {
Thread.sleep(20);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + " is looping of " + j + " for task of " + finalI
);
}
}
});
}
}
}
pool-1-thread-2 is looping of 1 for task of 2
pool-1-thread-1 is looping of 1 for task of 1
pool-1-thread-8 is looping of 1 for task of 8
pool-1-thread-9 is looping of 1 for task of 9
pool-1-thread-6 is looping of 1 for task of 6
pool-1-thread-3 is looping of 1 for task of 3
pool-1-thread-7 is looping of 1 for task of 7
pool-1-thread-4 is looping of 1 for task of 4
pool-1-thread-5 is looping of 1 for task of 5
pool-1-thread-6 is looping of 2 for task of 6
pool-1-thread-5 is looping of 2 for task of 5
pool-1-thread-2 is looping of 2 for task of 2
pool-1-thread-1 is looping of 2 for task of 1
pool-1-thread-7 is looping of 2 for task of 7
pool-1-thread-8 is looping of 2 for task of 8
pool-1-thread-3 is looping of 2 for task of 3
pool-1-thread-9 is looping of 2 for task of 9
pool-1-thread-4 is looping of 2 for task of 4
pool-1-thread-5 is looping of 3 for task of 5
pool-1-thread-9 is looping of 3 for task of 9
pool-1-thread-1 is looping of 3 for task of 1
pool-1-thread-2 is looping of 3 for task of 2
pool-1-thread-8 is looping of 3 for task of 8
pool-1-thread-3 is looping of 3 for task of 3
pool-1-thread-7 is looping of 3 for task of 7
pool-1-thread-6 is looping of 3 for task of 6
pool-1-thread-4 is looping of 3 for task of 4
pool-1-thread-2 is looping of 4 for task of 2
pool-1-thread-6 is looping of 4 for task of 6
pool-1-thread-4 is looping of 4 for task of 4
pool-1-thread-7 is looping of 4 for task of 7
pool-1-thread-1 is looping of 4 for task of 1
pool-1-thread-9 is looping of 4 for task of 9
pool-1-thread-3 is looping of 4 for task of 3
pool-1-thread-5 is looping of 4 for task of 5
pool-1-thread-8 is looping of 4 for task of 8
pool-1-thread-6 is looping of 5 for task of 6
pool-1-thread-9 is looping of 5 for task of 9
pool-1-thread-5 is looping of 5 for task of 5
pool-1-thread-8 is looping of 5 for task of 8
pool-1-thread-3 is looping of 5 for task of 3
pool-1-thread-1 is looping of 5 for task of 1
pool-1-thread-7 is looping of 5 for task of 7
pool-1-thread-4 is looping of 5 for task of 4
pool-1-thread-2 is looping of 5 for task of 2
pool-1-thread-6 is looping of 6 for task of 6
pool-1-thread-2 is looping of 6 for task of 2
pool-1-thread-4 is looping of 6 for task of 4
pool-1-thread-7 is looping of 6 for task of 7
pool-1-thread-3 is looping of 6 for task of 3
pool-1-thread-1 is looping of 6 for task of 1
pool-1-thread-5 is looping of 6 for task of 5
pool-1-thread-8 is looping of 6 for task of 8
pool-1-thread-9 is looping of 6 for task of 9
pool-1-thread-4 is looping of 7 for task of 4
pool-1-thread-3 is looping of 7 for task of 3
pool-1-thread-5 is looping of 7 for task of 5
pool-1-thread-1 is looping of 7 for task of 1
pool-1-thread-9 is looping of 7 for task of 9
pool-1-thread-8 is looping of 7 for task of 8
pool-1-thread-7 is looping of 7 for task of 7
pool-1-thread-6 is looping of 7 for task of 6
pool-1-thread-2 is looping of 7 for task of 2
pool-1-thread-9 is looping of 8 for task of 9
pool-1-thread-5 is looping of 8 for task of 5
pool-1-thread-7 is looping of 8 for task of 7
pool-1-thread-1 is looping of 8 for task of 1
pool-1-thread-3 is looping of 8 for task of 3
pool-1-thread-4 is looping of 8 for task of 4
pool-1-thread-8 is looping of 8 for task of 8
pool-1-thread-6 is looping of 8 for task of 6
pool-1-thread-2 is looping of 8 for task of 2
pool-1-thread-5 is looping of 9 for task of 5
pool-1-thread-2 is looping of 9 for task of 2
pool-1-thread-4 is looping of 9 for task of 4
pool-1-thread-6 is looping of 9 for task of 6
pool-1-thread-8 is looping of 9 for task of 8
pool-1-thread-3 is looping of 9 for task of 3
pool-1-thread-1 is looping of 9 for task of 1
pool-1-thread-7 is looping of 9 for task of 7
pool-1-thread-9 is looping of 9 for task of 9
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。
1.4 newScheduledThreadPool
public class ThreadPoolTest {
public static void main(String[] args) {
System.out.println("init");
Executors.newScheduledThreadPool(3).schedule(
new Runnable() {
@Override
public void run() {
System.out.println("Done");
}
}, 3, TimeUnit.SECONDS
);
}
}
init
Done
表示延迟3秒执行。
定期执行
public class ThreadPoolTest {
public static void main(String[] args) {
Executors.newScheduledThreadPool(3).scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
System.out.println("每三秒执行一次");
}
},2,3,TimeUnit.SECONDS);
}
}
每三秒执行一次
每三秒执行一次
每三秒执行一次
每三秒执行一次
省略...
2 关闭线程池
shutdown()
public class ThreadPoolTest {
public static void main(String[] args) {
//固定线程池
ExecutorService threadPool = Executors.newFixedThreadPool(3);
//缓存线程池 池中的线程数量
//ExecutorService threadPool = Executors.newCachedThreadPool();
//单个线程
//ExecutorService threadPool = Executors.newSingleThreadExecutor();
for (int i = 1; i < 10; i++) {
int finalI = i;
threadPool.execute(new Runnable() {
@Override
public void run() {
for (int j = 1; j < 10; j++) {
try {
Thread.sleep(20);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + " is looping of " + j + " for task of " + finalI
);
}
}
});
}
threadPool.shutdown();
}
}
pool-1-thread-1 is looping of 1 for task of 1
pool-1-thread-2 is looping of 1 for task of 2
pool-1-thread-3 is looping of 1 for task of 3
pool-1-thread-1 is looping of 2 for task of 1
pool-1-thread-3 is looping of 2 for task of 3
pool-1-thread-2 is looping of 2 for task of 2
pool-1-thread-1 is looping of 3 for task of 1
pool-1-thread-2 is looping of 3 for task of 2
pool-1-thread-3 is looping of 3 for task of 3
pool-1-thread-1 is looping of 4 for task of 1
pool-1-thread-3 is looping of 4 for task of 3
pool-1-thread-2 is looping of 4 for task of 2
pool-1-thread-3 is looping of 5 for task of 3
pool-1-thread-1 is looping of 5 for task of 1
pool-1-thread-2 is looping of 5 for task of 2
pool-1-thread-3 is looping of 6 for task of 3
pool-1-thread-1 is looping of 6 for task of 1
pool-1-thread-2 is looping of 6 for task of 2
pool-1-thread-3 is looping of 7 for task of 3
pool-1-thread-1 is looping of 7 for task of 1
pool-1-thread-2 is looping of 7 for task of 2
pool-1-thread-3 is looping of 8 for task of 3
pool-1-thread-1 is looping of 8 for task of 1
pool-1-thread-2 is looping of 8 for task of 2
pool-1-thread-1 is looping of 9 for task of 1
pool-1-thread-3 is looping of 9 for task of 3
pool-1-thread-2 is looping of 9 for task of 2
pool-1-thread-1 is looping of 1 for task of 4
pool-1-thread-3 is looping of 1 for task of 5
pool-1-thread-2 is looping of 1 for task of 6
pool-1-thread-1 is looping of 2 for task of 4
pool-1-thread-3 is looping of 2 for task of 5
pool-1-thread-2 is looping of 2 for task of 6
pool-1-thread-1 is looping of 3 for task of 4
pool-1-thread-3 is looping of 3 for task of 5
pool-1-thread-2 is looping of 3 for task of 6
pool-1-thread-1 is looping of 4 for task of 4
pool-1-thread-3 is looping of 4 for task of 5
pool-1-thread-2 is looping of 4 for task of 6
pool-1-thread-3 is looping of 5 for task of 5
pool-1-thread-1 is looping of 5 for task of 4
pool-1-thread-2 is looping of 5 for task of 6
pool-1-thread-3 is looping of 6 for task of 5
pool-1-thread-1 is looping of 6 for task of 4
pool-1-thread-2 is looping of 6 for task of 6
pool-1-thread-3 is looping of 7 for task of 5
pool-1-thread-1 is looping of 7 for task of 4
pool-1-thread-2 is looping of 7 for task of 6
pool-1-thread-3 is looping of 8 for task of 5
pool-1-thread-1 is looping of 8 for task of 4
pool-1-thread-2 is looping of 8 for task of 6
pool-1-thread-3 is looping of 9 for task of 5
pool-1-thread-1 is looping of 9 for task of 4
pool-1-thread-2 is looping of 9 for task of 6
pool-1-thread-1 is looping of 1 for task of 8
pool-1-thread-2 is looping of 1 for task of 9
pool-1-thread-3 is looping of 1 for task of 7
pool-1-thread-1 is looping of 2 for task of 8
pool-1-thread-2 is looping of 2 for task of 9
pool-1-thread-3 is looping of 2 for task of 7
pool-1-thread-1 is looping of 3 for task of 8
pool-1-thread-2 is looping of 3 for task of 9
pool-1-thread-3 is looping of 3 for task of 7
pool-1-thread-1 is looping of 4 for task of 8
pool-1-thread-2 is looping of 4 for task of 9
pool-1-thread-3 is looping of 4 for task of 7
pool-1-thread-2 is looping of 5 for task of 9
pool-1-thread-3 is looping of 5 for task of 7
pool-1-thread-1 is looping of 5 for task of 8
pool-1-thread-2 is looping of 6 for task of 9
pool-1-thread-3 is looping of 6 for task of 7
pool-1-thread-1 is looping of 6 for task of 8
pool-1-thread-2 is looping of 7 for task of 9
pool-1-thread-3 is looping of 7 for task of 7
pool-1-thread-1 is looping of 7 for task of 8
pool-1-thread-3 is looping of 8 for task of 7
pool-1-thread-1 is looping of 8 for task of 8
pool-1-thread-2 is looping of 8 for task of 9
pool-1-thread-3 is looping of 9 for task of 7
pool-1-thread-1 is looping of 9 for task of 8
pool-1-thread-2 is looping of 9 for task of 9
shutdownNow
public class ThreadPoolTest {
public static void main(String[] args) {
//固定线程池
ExecutorService threadPool = Executors.newFixedThreadPool(3);
//缓存线程池 池中的线程数量
//ExecutorService threadPool = Executors.newCachedThreadPool();
//单个线程
//ExecutorService threadPool = Executors.newSingleThreadExecutor();
for (int i = 1; i < 10; i++) {
int finalI = i;
threadPool.execute(new Runnable() {
@Override
public void run() {
for (int j = 1; j < 10; j++) {
try {
Thread.sleep(20);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + " is looping of " + j + " for task of " + finalI
);
}
}
});
}
threadPool.shutdownNow();
}
}
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at ThreadPoolTest$1.run(ThreadPoolTest.java:23)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.InterruptedException: sleep interrupted
pool-1-thread-3 is looping of 1 for task of 3
at java.lang.Thread.sleep(Native Method)
at ThreadPoolTest$1.run(ThreadPoolTest.java:23)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
pool-1-thread-2 is looping of 1 for task of 2
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at ThreadPoolTest$1.run(ThreadPoolTest.java:23)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
pool-1-thread-1 is looping of 1 for task of 1
pool-1-thread-3 is looping of 2 for task of 3
pool-1-thread-1 is looping of 2 for task of 1
pool-1-thread-2 is looping of 2 for task of 2
pool-1-thread-2 is looping of 3 for task of 2
pool-1-thread-1 is looping of 3 for task of 1
pool-1-thread-3 is looping of 3 for task of 3
pool-1-thread-2 is looping of 4 for task of 2
pool-1-thread-3 is looping of 4 for task of 3
pool-1-thread-1 is looping of 4 for task of 1
pool-1-thread-2 is looping of 5 for task of 2
pool-1-thread-1 is looping of 5 for task of 1
pool-1-thread-3 is looping of 5 for task of 3
pool-1-thread-1 is looping of 6 for task of 1
pool-1-thread-2 is looping of 6 for task of 2
pool-1-thread-3 is looping of 6 for task of 3
pool-1-thread-1 is looping of 7 for task of 1
pool-1-thread-3 is looping of 7 for task of 3
pool-1-thread-2 is looping of 7 for task of 2
pool-1-thread-1 is looping of 8 for task of 1
pool-1-thread-3 is looping of 8 for task of 3
pool-1-thread-2 is looping of 8 for task of 2
pool-1-thread-3 is looping of 9 for task of 3
pool-1-thread-2 is looping of 9 for task of 2
pool-1-thread-1 is looping of 9 for task of 1
2.1 shutdown和shutdownNow的区别
shutdown只是将线程池的状态设置为SHUTWDOWN状态，正在执行的任务会继续执行下去，没有被执行的则中断。而shutdownNow则是将线程池的状态设置为STOP，正在执行的任务则被停止，没被执行任务的则返回。
2.3 源码分析shutdown和shutdownNow
1.shutdown源码
public void shutdown() {
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
checkShutdownAccess();
advanceRunState(SHUTDOWN);
interruptIdleWorkers();
onShutdown(); // hook for ScheduledThreadPoolExecutor
} finally {
mainLock.unlock();
}
tryTerminate();
}
2.shutdownNow源码
public List<Runnable> shutdownNow() {
List<Runnable> tasks;
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
checkShutdownAccess();
advanceRunState(STOP);
interruptWorkers();
tasks = drainQueue();
} finally {
mainLock.unlock();
}
tryTerminate();
return tasks;
}
从源码可以很清晰的看出两者的区别，shutdown使用了以后会置状态为SHUTDOWN，而shutdownNow为STOP。此外，shutdownNow会返回任务列表。
2.3 线程状态知识延伸
在ThreadPoolExecutor中定义了关于线程状态的几个变量如下：
// runState is stored in the high-order bits
private static final int RUNNING = -1 << COUNT_BITS;
private static final int SHUTDOWN = 0 << COUNT_BITS;
private static final int STOP = 1 << COUNT_BITS;
private static final int TIDYING = 2 << COUNT_BITS;
private static final int TERMINATED = 3 << COUNT_BITS;
1.当创建线程池后，初始时，线程池处于RUNNING状态，此时线程池中的任务为0；
2.如果调用了shutdown()方法，则线程池处于SHUTDOWN状态，此时线程池不能够接受新的任务，它会等待所有任务执行完毕；
3.如果调用了shutdownNow()方法，则线程池处于STOP状态，此时线程池不能接受新的任务，并且会去尝试终止正在执行的任务；
4.当所有的任务已终止，ctl记录的”任务数量”为0，线程池会变为TIDYING状态。接着会执行terminated()函数。
5.线程池处在TIDYING状态时，执行完terminated()之后，就会由 TIDYING -> TERMINATED，线程池被设置为TERMINATED状态。
总结
线程池的作用：
线程池作用就是限制系统中执行线程的数量。
根据系统的环境情况，可以自动或手动设置线程数量，达到运行的最佳效果；少了浪费了系统资源，多了造成系统拥挤效率不高。用线程池控制线程数量，其他线程排队等候。一个任务执行完毕，再从队列的中取最前面的任务开始执行。若队列中没有等待进程，线程池的这一资源处于等待。当一个新任务需要运行时，如果线程池 中有等待的工作线程，就可以开始运行了；否则进入等待队列。
为什么要用线程池:
1.减少了创建和销毁线程的次数，每个工作线程都可以被重复利用，可执行多个任务。
2.可以根据系统的承受能力，调整线程池中工作线线程的数目，防止因为消耗过多的内存，而把服务器累趴下(每个线程需要大约1MB内存，线程开的越多，消耗的内存也就越大，最后死机)。
