基本方法学习
线程池是我们经常使用的工具,也是面试必问的知识点,那么如何优雅的关闭线程池那?
线程池相信大家都使用过,但是使用完成之后如何关闭线程池大家真的未必真的会使用。有人可能会说调用shutdown
或者shutdownNow
就可以了,真的有那么简单吗?如果你关闭线程池的姿势不正确,最严重的情况会导致线程一直存在系统中。
-
shutDown:通知线程池启动有序关闭,执行线程池之前已经提交的任务,但是不再接受新的任务。调用shutDown后再提交任务将会抛出
RejectedExecutionException
异常。 -
shutDownNow:尝试立即停止所有已经提交的任务,并会返回正在等待执行(未执行)的任务列表。shutDownNow通过向线程池中的线程发送一个中断请求而中止线程,如果线程池中运行了会抛出
InterruptedException
的程序,将会抛出一个InterruptedException
。如过这个线程不能响应中断那么可能永远无法被终止。 -
isTerminated:所有的任务都被关闭返回true,否则返回false。只有调用了shutDown或者shutDownNow,
isTerminated
才可能为true。 -
awaitTermination(long timeout, TimeUnit unit) throws InterruptedException:阻塞当前线程直到
- 所有任务执行完毕
- 或者超时
- 或者当前线程被中断
如果所有任务都关闭,则返回true,否则返回false。
优雅关闭线程池的正确姿势
- step1:执行shutdown方法,等待所有任务执行完毕并拒绝新任务的提交。
- step2:执行awaitTermination(long timeout,TimeUnit unit),指定超时时间,判断是是否已经关闭所有任务,防止线程永远无法关闭。
- step3:如果step2返回fasle,或者被中断。调用shutDownNow方法立即关闭线程池所有任务。
dubbo关闭线程池工具类学习
public class ExecutorUtil {
private static final Logger logger = LoggerFactory.getLogger(ExecutorUtil.class);
private static final ThreadPoolExecutor shutdownExecutor = new ThreadPoolExecutor(0, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>(100),
new NamedThreadFactory("Close-ExecutorService-Timer", true));
public static boolean isTerminated(Executor executor) {
if (executor instanceof ExecutorService) {
if (((ExecutorService) executor).isTerminated()) {
return true;
}
}
return false;
}
/**
* Use the shutdown pattern from:
* https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html
* @param executor the Executor to shutdown
* @param timeout the timeout in milliseconds before termination
*/
public static void gracefulShutdown(Executor executor, int timeout) {
if (!(executor instanceof ExecutorService) || isTerminated(executor)) {
return;
}
final ExecutorService es = (ExecutorService) executor;
try {
// Disable new tasks from being submitted
es.shutdown();
} catch (SecurityException ex2) {
return;
} catch (NullPointerException ex2) {
return;
}
try {
// Wait a while for existing tasks to terminate
if (!es.awaitTermination(timeout, TimeUnit.MILLISECONDS)) {
es.shutdownNow();
}
} catch (InterruptedException ex) {
es.shutdownNow();
Thread.currentThread().interrupt();
}
if (!isTerminated(es)) {
newThreadToCloseExecutor(es);
}
}
public static void shutdownNow(Executor executor, final int timeout) {
if (!(executor instanceof ExecutorService) || isTerminated(executor)) {
return;
}
final ExecutorService es = (ExecutorService) executor;
try {
es.shutdownNow();
} catch (SecurityException ex2) {
return;
} catch (NullPointerException ex2) {
return;
}
try {
es.awaitTermination(timeout, TimeUnit.MILLISECONDS);
} catch (InterruptedException ex) {
Thread.currentThread().interrupt();
}
if (!isTerminated(es)) {
newThreadToCloseExecutor(es);
}
}
private static void newThreadToCloseExecutor(final ExecutorService es) {
if (!isTerminated(es)) {
shutdownExecutor.execute(new Runnable() {
@Override
public void run() {
try {
for (int i = 0; i < 1000; i++) {
es.shutdownNow();
if (es.awaitTermination(10, TimeUnit.MILLISECONDS)) {
break;
}
}
} catch (InterruptedException ex) {
Thread.currentThread().interrupt();
} catch (Throwable e) {
logger.warn(e.getMessage(), e);
}
}
});
}
}
}