1 Executor.execute
public interface Executor {
在将来的某个时间执行给定的可运行的任务。该可运行的任务可以在新线程、池线程或调用线程中执行，由Executor实现决定。
参数： command–可运行的任务
投掷： RejectedExecutionException–如果无法接受执行此任务
NullPointerException–如果命令为空
void execute(Runnable command);
}
2 ExecutorService.shutdown
public interface ExecutorService extends Executor {
1、停止接收新的submit的任务；
2、已经提交的任务（包括正在跑的和队列中等待的）,会继续执行完成；
3、等到第2步完成后，才真正停止；
void shutdown();
}
实例如下：
public class ThreadPoolExecutorCloseTest {
public static void main(String[] args) {
ExecutorService executorService = new ThreadPoolExecutor(10,
20,
30,
TimeUnit.SECONDS,
new ArrayBlockingQueue<>(1),
Thread::new,
new ThreadPoolExecutor.AbortPolicy());
IntStream.range(0, 20).boxed().forEach(i -> {
executorService.execute(() -> {
try {
TimeUnit.SECONDS.sleep(10);
System.out.println(Thread.currentThread().getName() + " [ " + i + " ] finish done.");
} catch (InterruptedException e) {
e.printStackTrace();
}
});
});
/**
* 1、停止接收新的submit的任务；
* 2、已经提交的任务（包括正在跑的和队列中等待的）会继续执行完成；
* 3、等到第2步完成后，才真正停止；
*/
executorService.shutdown();
System.out.println("==============over==============");
}
}
线程真正停止了！
==============over==============
Thread-15 [ 16 ] finish done.
Thread-9 [ 9 ] finish done.
Thread-16 [ 17 ] finish done.
Thread-7 [ 7 ] finish done.
Thread-12 [ 13 ] finish done.
Thread-5 [ 5 ] finish done.
Thread-4 [ 4 ] finish done.
Thread-3 [ 3 ] finish done.
Thread-1 [ 1 ] finish done.
Thread-11 [ 12 ] finish done.
Thread-6 [ 6 ] finish done.
Thread-17 [ 18 ] finish done.
Thread-10 [ 11 ] finish done.
Thread-13 [ 14 ] finish done.
Thread-18 [ 19 ] finish done.
Thread-8 [ 8 ] finish done.
Thread-14 [ 15 ] finish done.
Thread-2 [ 2 ] finish done.
Thread-0 [ 0 ] finish done.
Thread-12 [ 10 ] finish done.
Process finished with exit code 0
3 ExecutorService.awaitTermination
当前线程阻塞，直到：
1、等所有已提交的任务（包括正在跑的和队列中等待的）执行完；
2、或者 等超时时间到了（timeout 和 TimeUnit设定的时间）；
3、或者 线程被中断，抛出InterruptedException
然后会监测 ExecutorService 是否已经关闭，返回true（shutdown请求后所有任务执行完毕）或false（已超时）
boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException;
示例如下：
public class ThreadPoolExecutorCloseTest {
public static void main(String[] args) throws InterruptedException {
ExecutorService executorService = new ThreadPoolExecutor(10,
20,
30,
TimeUnit.SECONDS,
new ArrayBlockingQueue<>(1),
Thread::new,
new ThreadPoolExecutor.AbortPolicy());
IntStream.range(0, 20).boxed().forEach(i -> {
executorService.execute(() -> {
try {
TimeUnit.SECONDS.sleep(10);
System.out.println(Thread.currentThread().getName() + " [ " + i + " ] finish done.");
} catch (InterruptedException e) {
e.printStackTrace();
}
});
});
executorService.shutdown();
/**
* 当前线程阻塞，直到：
* 1、等所有已提交的任务（包括正在跑的和队列中等待的）执行完
* 2、或者 等超时时间到了（timeout 和 TimeUnit设定的时间）
* 3、或者 线程被中断，抛出InterruptedException
* 然后会监测 ExecutorService 是否已经关闭，返回true（shutdown请求后所有任务执行完毕）或false（已超时）
*/
boolean b = executorService.awaitTermination(30, TimeUnit.SECONDS);
System.out.println(b);
System.out.println("==============over==============");
}
线程真正停止！
Thread-16 [ 17 ] finish done.
Thread-0 [ 0 ] finish done.
Thread-14 [ 15 ] finish done.
Thread-13 [ 14 ] finish done.
Thread-7 [ 7 ] finish done.
Thread-3 [ 3 ] finish done.
Thread-2 [ 2 ] finish done.
Thread-5 [ 5 ] finish done.
Thread-1 [ 1 ] finish done.
Thread-17 [ 18 ] finish done.
Thread-11 [ 12 ] finish done.
Thread-12 [ 13 ] finish done.
Thread-10 [ 11 ] finish done.
Thread-18 [ 19 ] finish done.
Thread-9 [ 9 ] finish done.
Thread-6 [ 6 ] finish done.
Thread-8 [ 8 ] finish done.
Thread-15 [ 16 ] finish done.
Thread-4 [ 4 ] finish done.
Thread-13 [ 10 ] finish done.
true
==============over==============
Process finished with exit code 0
4 shutdownNow()
停止接收新任务，原来的任务停止执行
1、跟 shutdown() 一样，先停止接收新submit的任务；
2、忽略队列里等待的任务；
3、尝试将正在执行的任务interrupt中断；
4、返回未执行的任务列表 — new ArrayBlockingQueue<>(8)
说明：它试图终止线程的方法是通过调用 Thread.interrupt() 方法来实现的，这种方法的作用有限，如果线程中没有sleep 、wait、Condition、定时锁等应用, interrupt() 方法是无法中断当前的线程的。所以，shutdownNow() 并不代表线程池就一定立即就能退出，它也可能必须要等待所有正在执行的任务都执行完成了才能退出。但是大多数时候是能立即退出的。
public class ThreadPoolExecutorCloseTest {
public static void main(String[] args) {
ExecutorService executorService = new ThreadPoolExecutor(10,
20,
30,
TimeUnit.SECONDS,
new ArrayBlockingQueue<>(8),
Thread::new,
new ThreadPoolExecutor.AbortPolicy());
IntStream.range(0, 20).boxed().forEach(i -> {
executorService.execute(() -> {
try {
TimeUnit.SECONDS.sleep(10);
System.out.println(Thread.currentThread().getName() + " [ " + i + " ] finish done.");
} catch (InterruptedException e) {
// e.printStackTrace();
}
});
});
shutdownNow(executorService);
System.out.println("==============over==============");
}
private static void shutdownNow(ExecutorService executorService) {
List<Runnable> runnableList = Lists.newArrayList();
try {
runnableList = executorService.shutdownNow();
} catch (Exception e) {
e.printStackTrace();
}
System.out.println(runnableList.size());
}
8
==============over==============
Process finished with exit code 0
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。
| shutdown | shutdownNow |
|---|---|
| shutdown调用的是advanceRunState(SHUTDOWN) | shutdownNow调用的是(STOP) |
| shutdown调用的是中断空闲的Workers | shutdownNow调用的是中断所有的Workers |
| shutdownNow会把所有任务队列中的任务取出来，返回一个任务列表 |
advanceRunState区别:
/**
* 从运行的状态过渡到targetState
* 如果当前已经大于了targetState，就什么都不做。
*/
private void advanceRunState(int targetState) {
for (;;) {
int c = ctl.get();
if (runStateAtLeast(c, targetState) ||
ctl.compareAndSet(c, ctlOf(targetState, workerCountOf(c))))
break;
}
}
targetState参数的使用值只有两个：SHUTDOWN与STOP
SHUTDOWN值为0
STOP值为1<<29 = 2^29
假设传的参数是SHUTDOWN：
ctlOf(targetState, workerCountOf©) = workerCountOf© > 0，一般就是线程池的个数
假设传的参数是STOP： 2^29:
ctlOf(targetState, workerCountOf©) = 2^29 + 2 , 为STOP状态
5 长时间未运行完的线程处理
package com.thread.excutor;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.stream.IntStream;
public class ThreadPoolExecutorLongTimeTest {
public static void main(String[] args) {
ExecutorService executorService = new ThreadPoolExecutor(10,
20,
30,
TimeUnit.SECONDS,
new ArrayBlockingQueue<>(8),
Thread::new,
new ThreadPoolExecutor.AbortPolicy());
IntStream.range(0, 10).boxed().forEach(item -> {
executorService.submit(() -> {
while (true) {
}
});
});
try {
executorService.shutdown();
executorService.awaitTermination(5, TimeUnit.SECONDS);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
System.out.println("===============over================");
}
}
线程池一直活着，无法停止！
package com.thread.excutor;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.stream.IntStream;
public class ThreadPoolExecutorLongTimeTest {
public static void main(String[] args) {
ExecutorService executorService = new ThreadPoolExecutor(10,
20,
30,
TimeUnit.SECONDS,
new ArrayBlockingQueue<>(8),
target -> {
Thread thread = new Thread(target);
thread.setDaemon(true);
return thread;
},
new ThreadPoolExecutor.AbortPolicy());
IntStream.range(0, 10).boxed().forEach(item -> {
executorService.submit(() -> {
while (true) {
}
});
});
try {
executorService.shutdown();
executorService.awaitTermination(5, TimeUnit.SECONDS); // 最多的期待时间
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
System.out.println("===============over================");
}
}
ok！设置守护线程的手段！
