在Java中使用超时调用阻塞方法是否有一种标准的好方法?我希望能够做到:
// call something.blockingMethod();
// if it hasn't come back within 2 seconds, forget it
如果这是有道理的。
感谢。
答案 0 :(得分:130)
你可以使用Executor:
ExecutorService executor = Executors.newCachedThreadPool();
Callable<Object> task = new Callable<Object>() {
public Object call() {
return something.blockingMethod();
}
};
Future<Object> future = executor.submit(task);
try {
Object result = future.get(5, TimeUnit.SECONDS);
} catch (TimeoutException ex) {
// handle the timeout
} catch (InterruptedException e) {
// handle the interrupts
} catch (ExecutionException e) {
// handle other exceptions
} finally {
future.cancel(true); // may or may not desire this
}
如果future.get
在5秒内没有返回,则会抛出TimeoutException
。可以在TimeUnit
中以秒,分钟,毫秒或任何可用单位配置超时。
有关详细信息,请参阅JavaDoc。
答案 1 :(得分:9)
您可以将呼叫包裹在FutureTask
中,并使用get()的超时版本。
请参阅http://java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/FutureTask.html
答案 2 :(得分:3)
There is also an AspectJ solution for that with jcabi-aspects library.
@Timeable(limit = 30, unit = TimeUnit.MINUTES)
public Soup cookSoup() {
// Cook soup, but for no more than 30 minutes (throw and exception if it takes any longer
}
It can't get more succinct, but you have to depend on AspectJ and introduce it in your build lifecycle, of course.
There is an article explaining it further: Limit Java Method Execution Time
答案 3 :(得分:2)
另见Guava的TimeLimiter在幕后使用Executor。
答案 4 :(得分:1)
Thread thread = new Thread(new Runnable() {
public void run() {
something.blockingMethod();
}
});
thread.start();
thread.join(2000);
if (thread.isAlive()) {
thread.stop();
}
注意,不推荐使用stop,更好的选择是设置一些volatile布尔标志,在blockingMethod()里面检查并退出,如下所示:
import org.junit.*;
import java.util.*;
import junit.framework.TestCase;
public class ThreadTest extends TestCase {
static class Something implements Runnable {
private volatile boolean stopRequested;
private final int steps;
private final long waitPerStep;
public Something(int steps, long waitPerStep) {
this.steps = steps;
this.waitPerStep = waitPerStep;
}
@Override
public void run() {
blockingMethod();
}
public void blockingMethod() {
try {
for (int i = 0; i < steps && !stopRequested; i++) {
doALittleBit();
}
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
}
public void doALittleBit() throws InterruptedException {
Thread.sleep(waitPerStep);
}
public void setStopRequested(boolean stopRequested) {
this.stopRequested = stopRequested;
}
}
@Test
public void test() throws InterruptedException {
final Something somethingRunnable = new Something(5, 1000);
Thread thread = new Thread(somethingRunnable);
thread.start();
thread.join(2000);
if (thread.isAlive()) {
somethingRunnable.setStopRequested(true);
thread.join(2000);
assertFalse(thread.isAlive());
} else {
fail("Exptected to be alive (5 * 1000 > 2000)");
}
}
}
答案 5 :(得分:1)
试试这个。更简单的解决方案保证if block在时间限制内没有执行。该过程将终止并抛出异常。
try {
TimeoutBlock timeoutBlock = new TimeoutBlock(10 * 60 * 1000);//set timeout in milliseconds
Runnable block=new Runnable() {
@Override
public void run() {
//TO DO write block of code
}
};
timeoutBlock.addBlock(block);// execute the runnable block
} catch (Throwable e) {
//catch the exception here . Which is block didn't execute within the time limit
}
示例:
{{1}}
答案 6 :(得分:1)
人们尝试以多种方式实现这一点真的很棒。但事实是,没有办法。
大多数开发人员都将尝试将阻塞调用放在另一个线程中,并设置一个将来的计时器。但是Java中没有办法从外部停止线程,更不用说一些非常具体的情况了,例如Thread.sleep()和Lock.lockInterruptably()方法,这些方法显式地处理线程中断。
所以实际上您只有3个通用选项:
将阻塞调用放在新线程上,如果时间到了,您就继续前进,让该线程挂起。在这种情况下,您应确保将线程设置为Daemon线程。这样,线程将不会阻止您的应用程序终止。
使用非阻塞Java API。因此,例如对于网络,请使用NIO2并使用非阻塞方法。要从控制台读取,请在阻止等之前使用Scanner.hasNext()。
如果阻塞调用不是IO,而是逻辑,则可以重复检查Thread.isInterrupted()
以检查它是否在外部中断,并在该线程上进行另一个线程调用thread.interrupt()
。阻塞线程
会真正地了解这些基础知识。它实际上讨论了这些特定的限制和场景,以及如何在其中一场讲座中探讨这些限制和场景。
我个人尝试在不使用阻塞调用的情况下进行编程。例如,有一些工具包,例如Vert.x,可以非常轻松,高效地以非阻塞方式异步执行IO,而无需进行IO操作。
我希望对您有帮助
答案 7 :(得分:0)
假设blockingMethod
只是睡了一些毫秒:
public void blockingMethod(Object input) {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
我的解决方案是使用wait()
和synchronized
,如下所示:
public void blockingMethod(final Object input, long millis) {
final Object lock = new Object();
new Thread(new Runnable() {
@Override
public void run() {
blockingMethod(input);
synchronized (lock) {
lock.notify();
}
}
}).start();
synchronized (lock) {
try {
// Wait for specific millis and release the lock.
// If blockingMethod is done during waiting time, it will wake
// me up and give me the lock, and I will finish directly.
// Otherwise, when the waiting time is over and the
// blockingMethod is still
// running, I will reacquire the lock and finish.
lock.wait(millis);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
所以你可以替换
something.blockingMethod(input)
到
something.blockingMethod(input, 2000)
希望它有所帮助。
答案 8 :(得分:0)
您需要一个circuit breaker实现,就像GitHub上failsafe项目中的实现一样。
答案 9 :(得分:0)
我在这里给您完整的代码。您可以使用您的方法来代替我要调用的方法:
public class NewTimeout {
public String simpleMethod() {
return "simple method";
}
public static void main(String[] args) {
ExecutorService executor = Executors.newSingleThreadScheduledExecutor();
Callable<Object> task = new Callable<Object>() {
public Object call() throws InterruptedException {
Thread.sleep(1100);
return new NewTimeout().simpleMethod();
}
};
Future<Object> future = executor.submit(task);
try {
Object result = future.get(1, TimeUnit.SECONDS);
System.out.println(result);
} catch (TimeoutException ex) {
System.out.println("Timeout............Timeout...........");
} catch (InterruptedException e) {
// handle the interrupts
} catch (ExecutionException e) {
// handle other exceptions
} finally {
executor.shutdown(); // may or may not desire this
}
}
}
答案 10 :(得分:0)
在阻塞队列的特殊情况下:
通用 java.util.concurrent.SynchronousQueue
有一个带有超时参数的 poll
方法。