钩子方法的优点:
beforeExecute(Thread, Runnable)
和 afterExecute(Runnable, Throwable)
在执行每项任务之前和之后调用的
beforeExecute(Thread, Runnable
)和afterExecute(Runnable, Throwable)
方法。这些可以用来操纵执行环境;例如,重新初始化ThreadLocals,收集统计信息或添加日志条目
我正在使用自定义ThreadPoolExecutor
来处理未捕获的异常。我可以在try{} catch{}
和Runnable
中添加Callable
块,但假设您无法强制开发人员在相关的Runnable
和Callable任务中添加这些块。
此CustomThreadPoolExecutor
覆盖afterExecute
中的ThreadPoolExecutor
()方法,如下所示(我已将变量b值指定为零以模拟算术异常。
import java.util.concurrent.*;
import java.util.*;
class CustomThreadPoolExecutor extends ThreadPoolExecutor {
public CustomThreadPoolExecutor() {
super(1,10,60,TimeUnit.SECONDS,new ArrayBlockingQueue<Runnable>(1000));
}
protected void afterExecute(Runnable r, Throwable t) {
super.afterExecute(r, t);
if (t == null && r instanceof Future<?>) {
try {
Object result = ((Future<?>) r).get();
System.out.println(result);
} catch (CancellationException ce) {
t = ce;
} catch (ExecutionException ee) {
t = ee.getCause();
} catch (InterruptedException ie) {
Thread.currentThread().interrupt(); // ignore/reset
}
}
if (t != null)
t.printStackTrace();
}
}
public class CustomThreadPoolExecutorDemo{
public static void main(String args[]){
System.out.println("creating service");
//ExecutorService service = Executors.newFixedThreadPool(10);
CustomThreadPoolExecutor service = new CustomThreadPoolExecutor();
service.submit(new Runnable(){
public void run(){
int a=4, b = 0;
System.out.println("a and b="+a+":"+b);
System.out.println("a/b:"+(a/b));
System.out.println("Thread Name in Runnable after divide by zero:"+Thread.currentThread().getName());
}
});
service.shutdown();
}
}
由于submit()
隐藏了框架中的异常,因此我重写了afterExecute()
方法来捕获异常。
在此方法中,我使用以下语句添加了阻塞调用
Object result = ((Future<?>) r).get();
目前我有10个队列容量为1000的线程。假设我的Runnable
需要5秒才能完成。
通过覆盖afterExecute
()方法,我是否会产生任何性能开销或使用此方法的任何缺点?
答案 0 :(得分:1)
更好的解决方案,坚持从submit()
返回的Future,然后您可以在主线程中处理异常,而不是黑客执行程序为您打印出来。
另一种选择是使用一个公共基础Runnable来实现你想要的异常处理,例如:
public abstract class BaseRunnable implements Runnable {
public final run() {
try {
runImpl();
} catch(Throwable t) {
t.printStackTrace();
}
}
protected abstract runImpl() throws Exception;
}
答案 1 :(得分:1)
不,你的阻止调用不会带来开销,因为任务已经完成执行并且status >= NORMAL
正如您在void runWorker(Worker w)
beforeExecute(wt, task);
Throwable thrown = null;
try {
task.run();
} catch (RuntimeException x) {
thrown = x; throw x;
} catch (Error x) {
thrown = x; throw x;
} catch (Throwable x) {
thrown = x; throw new Error(x);
} finally {
afterExecute(task, thrown);
}