I'm trying to write a thread that I can delegate testing and evolution of a robot to while I sort the existing chromosomes by fitness in the main thread. Below is the initial fitness method. What I want to do here is to have each genome tested by a robotHandler as the tests are 30 - 40 seconds long. I will only be running one of these threads at any given time.
Currently I seem to get caught in the wait() section of the intialFitness method. This is my first attempt at multithreading so any help as to how to debug the problem or if someone can spot the issue that would be fantastic
The RobotInterface class is just a testing class at the moment, I have commented out the log4j and sleep declarations to try and rule these out (Incidentally log4j was not logging anything in the thread if that helps)
public synchronized ArrayList<Genome> initialFitness( ArrayList<Genome> population)
{
for ( int i = 0; i < population.size(); i++ )
{
candidateTest = new CandidateTest(population.get(i));
Thread robotHandler = new Thread(new RobotInterface( candidateTest));
while(! (candidateTest.finishedYet() ))
{
try
{
wait();
}
catch (InterruptedException e)
{
logger.debug("The initialFitness method was interrupted, this shouldn't happen");
}
}
population.set(i, candidateTest.getCandidate());
}
return population;
}
import org.apache.log4j.Logger;
import org.apache.log4j.PropertyConfigurator;
import java.util.Random;
The RobotInterface Class
public class RobotInterface implements Runnable
{
// create a serial connection
// transmit a string and check for response
// wait for evaluation
// take evaluation
private CandidateTest candidate;
private Random rng = new Random();
//protected static Logger logger = Logger.getLogger("Thread" + Thread.currentThread().getName());
public RobotInterface(CandidateTest test)
{
this.candidate = test;
//PropertyConfigurator.configure("log4j.properties");
}
public void evaluate (Genome genome)
{
//send to robot and return fitness
genome.setFitness(rng.nextDouble());
//logger.debug("fitness is " + genome.getFitness());
try
{
//logger.debug("Thread sleeping for 4 seconds");
//Thread.sleep(4000);
}
catch(Exception E)
{
}
}
public void run()
{
//logger.debug("entering run of Robot Interface");
//logger.debug("Send Genome via serial and wait for a response");
Genome testSubject = candidate.getCandidate();
evaluate(testSubject);
candidate.finished();
notifyAll();
}
}
The CandidateTest Class
public class CandidateTest
{
private volatile Genome candidate;
private volatile boolean testFinished = false;
public CandidateTest(Genome g)
{
candidate = g;
}
public synchronized Genome getCandidate()
{
return candidate;
}
public synchronized void finished()
{
testFinished = true;
}
public synchronized boolean finishedYet()
{
return testFinished;
}
}
First, you are not starting the robotHandler thread. So your main thread gets to wait() and then no other thread ever comes along to notify it.
Second, you call wait() on whatever class initialFitness belongs to, but you call notifyAll() on RobotInterface. So RobotInterface will notify everyone who is waiting on it (nobody) and your main code will continue to wait. You need to call notifyAll() on the same object on which you called wait().
I suggest
synchronized(candidateTest) {
candidateTest.wait();
}
and
candidateTest.notify();
Never seen where the Thread is started. Try:
Thread robotHandler = new Thread(new RobotInterface( candidateTest)).start();
so your notifyAll() is never called
Nathanial hit the nail on the head but I would suggest using the java.util.concurrent package if you are just getting started with concurrency in Java. Found a nice beginners article on DZone for you: http://java.dzone.com/articles/lazy-developers-introduction
using JConsole it seems i get a deadlock situation when 2 threads try to modify this object.
package com.steven.concurrent.assignment2.memoryallocator;
/*
* This seems to deadlock... cant see why though.
*/
public class MemAllocMonitor implements IMemoryAllocator {
private final int MAX_FREE = 50;
private int freePages = MAX_FREE;
//I think this would work, without even the need for sync blocks.....
// But only in the situaion where i would not have to check the bounds of the updates. If it was just modification, this would be
// fine....
//private volatile int freePages = 50;
public MemAllocMonitor(int pages){
assert(pages < MAX_FREE);
this.freePages = pages;
}
public MemAllocMonitor(){
}
#Override
public synchronized void request(int number) {
if(number < 0)
throw new IllegalArgumentException();
while(freePages - number < 0) {
System.out.println("No space....waiting...");
try {
this.wait();
} catch (Exception e) {}
}
freePages -= number;
System.out.println("Requested : " + number + " remaining " + freePages);
this.notifyAll();
}
#Override
public synchronized void release(int number) {
if(number < 0)
throw new IllegalArgumentException();
while(freePages + number > MAX_FREE) {
System.out.println("page table full....would be " + (number + freePages) );
try {
this.wait();
} catch (Exception e) {}
}
freePages += number;
System.out.println("Released : " + number + " remaining " + freePages);
this.notifyAll();
}
#Override
public int getFreePages() {
return freePages;
}
}
This object is accessed via a simple wrapper that implements runnable, and calls either method as shown below.
package com.steven.concurrent.assignment2.memoryallocator;
import concurrent.RandomGenerator;
import concurrent.Time;
public class MemAllocRequester implements Runnable, MemoryAllocatorAction{
private IMemoryAllocator memoryAllocator;
private volatile boolean shutdown = false;;
public MemAllocRequester(IMemoryAllocator memAlloc){
this.memoryAllocator = memAlloc;
}
#Override
public void run() {
while(!shutdown){
Time.delay(500);
memoryAllocator.request(RandomGenerator.integer(0, 30));
}
}
public void ShutDown(){
this.shutdown = true;
}
}
and
package com.steven.concurrent.assignment2.memoryallocator;
import concurrent.RandomGenerator;
import concurrent.Time;
public class MemAllocReleaser implements Runnable, MemoryAllocatorAction{
private IMemoryAllocator memoryAllocator;
private volatile boolean shutdown = false;;
public MemAllocReleaser(IMemoryAllocator memAlloc){
this.memoryAllocator = memAlloc;
}
#Override
public void run() {
while(!shutdown){
Time.delay(500);
memoryAllocator.release(RandomGenerator.integer(0, 30));
}
}
public void ShutDown(){
this.shutdown = true;
}
}
It is started off as such...
package com.steven.concurrent.assignment2.memoryallocator;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class MemAllocMain {
public static void main(String[] args){
ExecutorService executor = Executors.newFixedThreadPool(10);
//IMemoryAllocator memoryAllocator = new MemAllocSemaphore();
IMemoryAllocator memoryAllocator = new MemAllocMonitor();
System.out.println("Starting app with " + memoryAllocator.getFreePages() + " pages...");
Thread t1 = new Thread(new MemAllocRequester(memoryAllocator));
Thread t2 = new Thread(new MemAllocReleaser(memoryAllocator));
t1.setName("MEMORY REQUESTER £££££££££££££££££££");
t2.setName("MEMORY RELEASER £££££££££££££££££££");
executor.submit(t1);
executor.submit(t2);
}
}
I have implemented a solution using the semaphore class, but for some reason this is causing trouble using the default java monitor solution. It runs for about 30 seconds, then both threads go into their waiting state, even though the lock should be enforced.
The problem is that both threads are hitting the upper and lower bounds (50 and 0 respectively) at the same time. Both examples below highlight the deadlock.
Scenario 1
request(29) - freePages=21
request(30) - under 0 so waits
release(30) - over 50 so waits : deadlock
Scenario 2
request(29) - freePages=21
release(30) - over 50 so waits
request(30) - under 0 so waits : deadlock
I am not sure what the exact requirements are for the homework problem but you need to revisit the release and request methods. I see two viable solutions:
Change the release method so that it only releases up to MAX_FREE but will still return
Change the release method so that it can release a subset of the amount requested, notifyAll, reenter the wait so it can release the remaining amount.
Also, you are kind of using the ExecutionService wrong. The ExecutionService is what creates the Threads so there is no reason for you to create the threads like you are doing.
Thread t1 = new Thread(new MemAllocRequester(memoryAllocator));
Thread t2 = new Thread(new MemAllocReleaser(memoryAllocator));
The threads you are creating will actually never be 'started' as Threads. It is still working for you because the ExecutionService threads will call your Thread.run() which will call MemAlloc*.run(). i.e. your t1 and t2 threads just pass the run() call along and provide no value.
Your MemAllocRequester and MemAllocReleaser are Runnables so just pass those into the ExecutionService directly.
executor.submit(new MemAllocRequester(memoryAllocator));
executor.submit(new MemAllocReleaser(memoryAllocator));
I am supposed to process images in a multithreaded mode using Java. I may having varying number of images where as my number of threads are fixed. I have to process all the images using the fixed set of threads.
I am just stuck up on how to do it, I had a look ThreadExecutor and BlockingQueues etc...I am still not clear. What I am doing is,
- Get the images and add them in a LinkedBlockingQueue which has runnable code of the image processor.
- Create a threadpoolexecutor for which one of the arguements is the LinkedBlockingQueue earlier.
- Iterate through a for loop till the queue size and do a threadpoolexecutor.execute(linkedblockingqueue.poll).
- all i see is it processes only 100 images which is the minimum thread size passed in LinkedBlockingQueue size.
I see I am seriously wrong in my understanding somewhere, how do I process all the images in sets of 100(threads) until they are all done? Any examples or psuedocodes would be highly helpful
Thanks!
J
Here is a sample class that I wrote. The whole thing runs standalone and prints a number from 1 to 100 each from a ThreadPool. Pretty much all you need to do is update the Request class to pass in what you want and to re-implement ImageProcessor.
package com.rch.test;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
public class Executor
{
/**
* Class to encapsulate a request
*
* #author romain
*/
static class Request
{
String someText;
Request(String someText)
{
this.someText = someText;
}
public String getSomeText()
{
return someText;
}
}
/**
* Creates a Thread that listens on a queue to process messages
*
* #author romain
*/
static class ServerThread implements Runnable
{
private BlockingQueue<Request> queue = new LinkedBlockingQueue<Request>();
boolean stop = false;
/**
* Does all the work
*/
#Override
public void run()
{
ExecutorService pool = Executors.newFixedThreadPool(3);
try
{
while (!stop)
{
Request req = queue.poll(1000L, TimeUnit.MILLISECONDS);
if (req != null)
{
Runnable runnable = new Executor.ImageProcessor(req);
pool.execute(runnable);
}
}
}
catch (InterruptedException ie)
{
System.out.println("Log something here");
}
finally
{
pool.shutdown();
}
}
/**
* Accepts a message on the queue
* #param request
*/
public void accept(Request request)
{
queue.add(request);
}
public void stopProcessing()
{
stop = true;
}
}
/**
* class to do the actual work
* #author romain
*/
static class ImageProcessor implements Runnable
{
String someText;
ImageProcessor(Request req)
{
this.someText = req.getSomeText();
}
#Override
public void run()
{
System.out.println(someText);
// Process Image here
}
}
/**
* Test Harness
* #param args
*/
public static void main(String[] args)
{
// Initialize
ServerThread processor = new ServerThread();
Thread aThread = new Thread(processor);
aThread.start();
// Wait for Thread to start
try
{
Thread.sleep(500L);
}
catch (InterruptedException e1)
{
e1.printStackTrace();
}
for (int i = 0; i < 100; i++)
{
String text = "" + i;
Request aRequest = new Request(text);
processor.accept(aRequest);
}
// Give it enough time to finish
try
{
Thread.sleep(500L);
}
catch (InterruptedException e1)
{
e1.printStackTrace();
}
// Tell the thread to finish processing
processor.stopProcessing();
// Wait for the Thread to complete
try
{
aThread.join();
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
}
You can think of each processing operation being a 'task'. Place these tasks in a single queue, and have each thread consuming a task from this thread each time they complete a task.
Sun's tutorials is really good so i will just post the link Defining and Starting a Thread
Quote:
Threads are sometimes called lightweight processes. Both processes and threads provide an execution environment, but creating a new thread requires fewer resources than creating a new process.
Threads exist within a process — every process has at least one. Threads share the process's resources, including memory and open files. This makes for efficient, but potentially problematic, communication.
while(que is not empty)
start new set of image-processing-thread
I want to run a thread for some fixed amount of time. If it is not completed within that time, I want to either kill it, throw some exception, or handle it in some way. How can it be done?
One way of doing it as I figured out from this thread
is to use a TimerTask inside the run() method of the Thread.
Are there any better solutions for this?
EDIT: Adding a bounty as I needed a clearer answer. The ExecutorService code given below does not address my problem. Why should I sleep() after executing (some code - I have no handle over this piece of code)? If the code is completed and the sleep() is interrupted, how can that be a timeOut?
The task that needs to be executed is not in my control. It can be any piece of code. The problem is this piece of code might run into an infinite loop. I don't want that to happen. So, I just want to run that task in a separate thread. The parent thread has to wait till that thread finishes and needs to know the status of the task (i.e whether it timed out or some exception occured or if its a success). If the task goes into an infinite loop, my parent thread keeps on waiting indefinitely, which is not an ideal situation.
Indeed rather use ExecutorService instead of Timer, here's an SSCCE:
package com.stackoverflow.q2275443;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
public class Test {
public static void main(String[] args) throws Exception {
ExecutorService executor = Executors.newSingleThreadExecutor();
Future<String> future = executor.submit(new Task());
try {
System.out.println("Started..");
System.out.println(future.get(3, TimeUnit.SECONDS));
System.out.println("Finished!");
} catch (TimeoutException e) {
future.cancel(true);
System.out.println("Terminated!");
}
executor.shutdownNow();
}
}
class Task implements Callable<String> {
#Override
public String call() throws Exception {
Thread.sleep(4000); // Just to demo a long running task of 4 seconds.
return "Ready!";
}
}
Play a bit with the timeout argument in Future#get() method, e.g. increase it to 5 and you'll see that the thread finishes. You can intercept the timeout in the catch (TimeoutException e) block.
Update: to clarify a conceptual misunderstanding, the sleep() is not required. It is just used for SSCCE/demonstration purposes. Just do your long running task right there in place of sleep(). Inside your long running task, you should be checking if the thread is not interrupted as follows:
while (!Thread.interrupted()) {
// Do your long running task here.
}
There isn't a 100% reliable way to do this for any old task. The task has to be written with this ability in mind.
Core Java libraries like ExecutorService cancel asynchronous tasks with interrupt() calls on the worker thread. So, for example, if the task contains some sort of loop, you should be checking its interrupt status on each iteration. If the task is doing I/O operations, they should be interruptible too—and setting that up can be tricky. In any case, keep in mind that code has to actively check for interrupts; setting an interrupt doesn't necessarily do anything.
Of course, if your task is some simple loop, you can just check the current time at each iteration and give up when a specified timeout has elapsed. A worker thread isn't needed in that case.
Consider using an instance of ExecutorService. Both invokeAll() and invokeAny() methods are available with a timeout parameter.
The current thread will block until the method completes (not sure if this is desirable) either because the task(s) completed normally or the timeout was reached. You can inspect the returned Future(s) to determine what happened.
Assuming the thread code is out of your control:
From the Java documentation mentioned above:
What if a thread doesn't respond to Thread.interrupt?
In some cases, you can use application specific tricks. For example,
if a thread is waiting on a known socket, you can close the socket to
cause the thread to return immediately. Unfortunately, there really
isn't any technique that works in general. It should be noted that in
all situations where a waiting thread doesn't respond to
Thread.interrupt, it wouldn't respond to Thread.stop either. Such
cases include deliberate denial-of-service attacks, and I/O operations
for which thread.stop and thread.interrupt do not work properly.
Bottom Line:
Make sure all threads can be interrupted, or else you need specific knowledge of the thread - like having a flag to set. Maybe you can require that the task be given to you along with the code needed to stop it - define an interface with a stop() method. You can also warn when you failed to stop a task.
BalusC said:
Update: to clarify a conceptual misunderstanding, the sleep() is not required. It is just used for SSCCE/demonstration purposes. Just do your long running task right there in place of sleep().
But if you replace Thread.sleep(4000); with for (int i = 0; i < 5E8; i++) {} then it doesn't compile, because the empty loop doesn't throw an InterruptedException.
And for the thread to be interruptible, it needs to throw an InterruptedException.
This seems like a serious problem to me. I can't see how to adapt this answer to work with a general long-running task.
Edited to add: I reasked this as a new question: [ interrupting a thread after fixed time, does it have to throw InterruptedException? ]
I created a helper class just for this some time ago. Works great:
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
/**
* TimeOut class - used for stopping a thread that is taking too long
* #author Peter Goransson
*
*/
public class TimeOut {
Thread interrupter;
Thread target;
long timeout;
boolean success;
boolean forceStop;
CyclicBarrier barrier;
/**
*
* #param target The Runnable target to be executed
* #param timeout The time in milliseconds before target will be interrupted or stopped
* #param forceStop If true, will Thread.stop() this target instead of just interrupt()
*/
public TimeOut(Runnable target, long timeout, boolean forceStop) {
this.timeout = timeout;
this.forceStop = forceStop;
this.target = new Thread(target);
this.interrupter = new Thread(new Interrupter());
barrier = new CyclicBarrier(2); // There will always be just 2 threads waiting on this barrier
}
public boolean execute() throws InterruptedException {
// Start target and interrupter
target.start();
interrupter.start();
// Wait for target to finish or be interrupted by interrupter
target.join();
interrupter.interrupt(); // stop the interrupter
try {
barrier.await(); // Need to wait on this barrier to make sure status is set
} catch (BrokenBarrierException e) {
// Something horrible happened, assume we failed
success = false;
}
return success; // status is set in the Interrupter inner class
}
private class Interrupter implements Runnable {
Interrupter() {}
public void run() {
try {
Thread.sleep(timeout); // Wait for timeout period and then kill this target
if (forceStop) {
target.stop(); // Need to use stop instead of interrupt since we're trying to kill this thread
}
else {
target.interrupt(); // Gracefully interrupt the waiting thread
}
System.out.println("done");
success = false;
} catch (InterruptedException e) {
success = true;
}
try {
barrier.await(); // Need to wait on this barrier
} catch (InterruptedException e) {
// If the Child and Interrupter finish at the exact same millisecond we'll get here
// In this weird case assume it failed
success = false;
}
catch (BrokenBarrierException e) {
// Something horrible happened, assume we failed
success = false;
}
}
}
}
It is called like this:
long timeout = 10000; // number of milliseconds before timeout
TimeOut t = new TimeOut(new PhotoProcessor(filePath, params), timeout, true);
try {
boolean sucess = t.execute(); // Will return false if this times out
if (!sucess) {
// This thread timed out
}
else {
// This thread ran completely and did not timeout
}
} catch (InterruptedException e) {}
I think you should take a look at proper concurrency handling mechanisms (threads running into infinite loops doesn't sound good per se, btw). Make sure you read a little about the "killing" or "stopping" Threads topic.
What you are describing,sound very much like a "rendezvous", so you may want to take a look at the CyclicBarrier.
There may be other constructs (like using CountDownLatch for example) that can resolve your problem (one thread waiting with a timeout for the latch, the other should count down the latch if it has done it's work, which would release your first thread either after a timeout or when the latch countdown is invoked).
I usually recommend two books in this area: Concurrent Programming in Java and Java Concurrency in Practice.
In the solution given by BalusC, the main thread will stay blocked for the timeout period. If you have a thread pool with more than one thread, you will need the same number of additional thread that will be using Future.get(long timeout,TimeUnit unit) blocking call to wait and close the thread if it exceeds the timeout period.
A generic solution to this problem is to create a ThreadPoolExecutor Decorator that can add the timeout functionality. This Decorator class should create as many threads as ThreadPoolExecutor has, and all these threads should be used only to wait and close the ThreadPoolExecutor.
The generic class should be implemented like below:
import java.util.List;
import java.util.concurrent.*;
public class TimeoutThreadPoolDecorator extends ThreadPoolExecutor {
private final ThreadPoolExecutor commandThreadpool;
private final long timeout;
private final TimeUnit unit;
public TimeoutThreadPoolDecorator(ThreadPoolExecutor threadpool,
long timeout,
TimeUnit unit ){
super( threadpool.getCorePoolSize(),
threadpool.getMaximumPoolSize(),
threadpool.getKeepAliveTime(TimeUnit.MILLISECONDS),
TimeUnit.MILLISECONDS,
threadpool.getQueue());
this.commandThreadpool = threadpool;
this.timeout=timeout;
this.unit=unit;
}
#Override
public void execute(Runnable command) {
super.execute(() -> {
Future<?> future = commandThreadpool.submit(command);
try {
future.get(timeout, unit);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
} catch (ExecutionException | TimeoutException e) {
throw new RejectedExecutionException(e);
} finally {
future.cancel(true);
}
});
}
#Override
public void setCorePoolSize(int corePoolSize) {
super.setCorePoolSize(corePoolSize);
commandThreadpool.setCorePoolSize(corePoolSize);
}
#Override
public void setThreadFactory(ThreadFactory threadFactory) {
super.setThreadFactory(threadFactory);
commandThreadpool.setThreadFactory(threadFactory);
}
#Override
public void setMaximumPoolSize(int maximumPoolSize) {
super.setMaximumPoolSize(maximumPoolSize);
commandThreadpool.setMaximumPoolSize(maximumPoolSize);
}
#Override
public void setKeepAliveTime(long time, TimeUnit unit) {
super.setKeepAliveTime(time, unit);
commandThreadpool.setKeepAliveTime(time, unit);
}
#Override
public void setRejectedExecutionHandler(RejectedExecutionHandler handler) {
super.setRejectedExecutionHandler(handler);
commandThreadpool.setRejectedExecutionHandler(handler);
}
#Override
public List<Runnable> shutdownNow() {
List<Runnable> taskList = super.shutdownNow();
taskList.addAll(commandThreadpool.shutdownNow());
return taskList;
}
#Override
public void shutdown() {
super.shutdown();
commandThreadpool.shutdown();
}
}
The above decorator can be used as below:
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class Main {
public static void main(String[] args){
long timeout = 2000;
ThreadPoolExecutor threadPool = new ThreadPoolExecutor(3, 10, 0, TimeUnit.MILLISECONDS, new SynchronousQueue<>(true));
threadPool = new TimeoutThreadPoolDecorator( threadPool ,
timeout,
TimeUnit.MILLISECONDS);
threadPool.execute(command(1000));
threadPool.execute(command(1500));
threadPool.execute(command(2100));
threadPool.execute(command(2001));
while(threadPool.getActiveCount()>0);
threadPool.shutdown();
}
private static Runnable command(int i) {
return () -> {
System.out.println("Running Thread:"+Thread.currentThread().getName());
System.out.println("Starting command with sleep:"+i);
try {
Thread.sleep(i);
} catch (InterruptedException e) {
System.out.println("Thread "+Thread.currentThread().getName()+" with sleep of "+i+" is Interrupted!!!");
return;
}
System.out.println("Completing Thread "+Thread.currentThread().getName()+" after sleep of "+i);
};
}
}
I post you a piece of code which show a way how to solve the problem.
As exemple I'm reading a file.
You could use this method for another operation, but you need to implements the kill() method so that the main operation will be interrupted.
hope it helps
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
/**
* Main class
*
* #author el
*
*/
public class Main {
/**
* Thread which perform the task which should be timed out.
*
* #author el
*
*/
public static class MainThread extends Thread {
/**
* For example reading a file. File to read.
*/
final private File fileToRead;
/**
* InputStream from the file.
*/
final private InputStream myInputStream;
/**
* Thread for timeout.
*/
final private TimeOutThread timeOutThread;
/**
* true if the thread has not ended.
*/
boolean isRunning = true;
/**
* true if all tasks where done.
*/
boolean everythingDone = false;
/**
* if every thing could not be done, an {#link Exception} may have
* Happens.
*/
Throwable endedWithException = null;
/**
* Constructor.
*
* #param file
* #throws FileNotFoundException
*/
MainThread(File file) throws FileNotFoundException {
setDaemon(false);
fileToRead = file;
// open the file stream.
myInputStream = new FileInputStream(fileToRead);
// Instantiate the timeout thread.
timeOutThread = new TimeOutThread(10000, this);
}
/**
* Used by the {#link TimeOutThread}.
*/
public void kill() {
if (isRunning) {
isRunning = false;
if (myInputStream != null) {
try {
// close the stream, it may be the problem.
myInputStream.close();
} catch (IOException e) {
// Not interesting
System.out.println(e.toString());
}
}
synchronized (this) {
notify();
}
}
}
/**
* The task which should be timed out.
*/
#Override
public void run() {
timeOutThread.start();
int bytes = 0;
try {
// do something
while (myInputStream.read() >= 0) {
// may block the thread.
myInputStream.read();
bytes++;
// simulate a slow stream.
synchronized (this) {
wait(10);
}
}
everythingDone = true;
} catch (IOException e) {
endedWithException = e;
} catch (InterruptedException e) {
endedWithException = e;
} finally {
timeOutThread.kill();
System.out.println("-->read " + bytes + " bytes.");
isRunning = false;
synchronized (this) {
notifyAll();
}
}
}
}
/**
* Timeout Thread. Kill the main task if necessary.
*
* #author el
*
*/
public static class TimeOutThread extends Thread {
final long timeout;
final MainThread controlledObj;
TimeOutThread(long timeout, MainThread controlledObj) {
setDaemon(true);
this.timeout = timeout;
this.controlledObj = controlledObj;
}
boolean isRunning = true;
/**
* If we done need the {#link TimeOutThread} thread, we may kill it.
*/
public void kill() {
isRunning = false;
synchronized (this) {
notify();
}
}
/**
*
*/
#Override
public void run() {
long deltaT = 0l;
try {
long start = System.currentTimeMillis();
while (isRunning && deltaT < timeout) {
synchronized (this) {
wait(Math.max(100, timeout - deltaT));
}
deltaT = System.currentTimeMillis() - start;
}
} catch (InterruptedException e) {
// If the thread is interrupted,
// you may not want to kill the main thread,
// but probably yes.
} finally {
isRunning = false;
}
controlledObj.kill();
}
}
/**
* Start the main task and wait for the end.
*
* #param args
* #throws FileNotFoundException
*/
public static void main(String[] args) throws FileNotFoundException {
long start = System.currentTimeMillis();
MainThread main = new MainThread(new File(args[0]));
main.start();
try {
while (main.isRunning) {
synchronized (main) {
main.wait(1000);
}
}
long stop = System.currentTimeMillis();
if (main.everythingDone)
System.out.println("all done in " + (stop - start) + " ms.");
else {
System.out.println("could not do everything in "
+ (stop - start) + " ms.");
if (main.endedWithException != null)
main.endedWithException.printStackTrace();
}
} catch (InterruptedException e) {
System.out.println("You've killed me!");
}
}
}
Regards
Here is my really simple to use helper class to run or call piece of Java code :-)
This is based on the excellent answer from BalusC
package com.mycompany.util.concurrent;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
/**
* Calling {#link Callable#call()} or Running {#link Runnable#run()} code
* with a timeout based on {#link Future#get(long, TimeUnit))}
* #author pascaldalfarra
*
*/
public class CallableHelper
{
private CallableHelper()
{
}
public static final void run(final Runnable runnable, int timeoutInSeconds)
{
run(runnable, null, timeoutInSeconds);
}
public static final void run(final Runnable runnable, Runnable timeoutCallback, int timeoutInSeconds)
{
call(new Callable<Void>()
{
#Override
public Void call() throws Exception
{
runnable.run();
return null;
}
}, timeoutCallback, timeoutInSeconds);
}
public static final <T> T call(final Callable<T> callable, int timeoutInSeconds)
{
return call(callable, null, timeoutInSeconds);
}
public static final <T> T call(final Callable<T> callable, Runnable timeoutCallback, int timeoutInSeconds)
{
ExecutorService executor = Executors.newSingleThreadExecutor();
try
{
Future<T> future = executor.submit(callable);
T result = future.get(timeoutInSeconds, TimeUnit.SECONDS);
System.out.println("CallableHelper - Finished!");
return result;
}
catch (TimeoutException e)
{
System.out.println("CallableHelper - TimeoutException!");
if(timeoutCallback != null)
{
timeoutCallback.run();
}
}
catch (InterruptedException e)
{
e.printStackTrace();
}
catch (ExecutionException e)
{
e.printStackTrace();
}
finally
{
executor.shutdownNow();
executor = null;
}
return null;
}
}
The following snippet will start an operation in a separate thread, then wait for up to 10 seconds for the operation to complete. If the operation does not complete in time, the code will attempt to cancel the operation, then continue on its merry way. Even if the operation cannot be cancelled easily, the parent thread will not wait for the child thread to terminate.
ExecutorService executorService = getExecutorService();
Future<SomeClass> future = executorService.submit(new Callable<SomeClass>() {
public SomeClass call() {
// Perform long-running task, return result. The code should check
// interrupt status regularly, to facilitate cancellation.
}
});
try {
// Real life code should define the timeout as a constant or
// retrieve it from configuration
SomeClass result = future.get(10, TimeUnit.SECONDS);
// Do something with the result
} catch (TimeoutException e) {
future.cancel(true);
// Perform other error handling, e.g. logging, throwing an exception
}
The getExecutorService() method can be implemented in a number of ways. If you do not have any particular requirements, you can simply call Executors.newCachedThreadPool() for thread pooling with no upper limit on the number of threads.
One thing that I've not seen mentioned is that killing threads is generally a Bad Idea. There are techniques for making threaded methods cleanly abortable, but that's different to just killing a thread after a timeout.
The risk with what you're suggesting is that you probably don't know what state the thread will be in when you kill it - so you risk introducing instability. A better solution is to make sure your threaded code either doesn't hang itself, or will respond nicely to an abort request.
Great answer by BalusC's:
but Just to add that the timeout itself does not interrupt the thread itself. even if you are checking with while(!Thread.interrupted()) in your task. if you want to make sure thread is stopped you should also make sure future.cancel() is invoked when timeout exception is catch.
package com.stackoverflow.q2275443;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
public class Test {
public static void main(String[] args) throws Exception {
ExecutorService executor = Executors.newSingleThreadExecutor();
Future<String> future = executor.submit(new Task());
try {
System.out.println("Started..");
System.out.println(future.get(3, TimeUnit.SECONDS));
System.out.println("Finished!");
} catch (TimeoutException e) {
//Without the below cancel the thread will continue to live
// even though the timeout exception thrown.
future.cancel();
System.out.println("Terminated!");
}
executor.shutdownNow();
}
}
class Task implements Callable<String> {
#Override
public String call() throws Exception {
while(!Thread.currentThread.isInterrupted()){
System.out.println("Im still running baby!!");
}
}
}
I think the answer mainly depends on the task itself.
Is it doing one task over and over again?
Is it necessary that the timeout interrupts a currently running task immediately after it expires?
If the first answer is yes and the second is no, you could keep it as simple as this:
public class Main {
private static final class TimeoutTask extends Thread {
private final long _timeoutMs;
private Runnable _runnable;
private TimeoutTask(long timeoutMs, Runnable runnable) {
_timeoutMs = timeoutMs;
_runnable = runnable;
}
#Override
public void run() {
long start = System.currentTimeMillis();
while (System.currentTimeMillis() < (start + _timeoutMs)) {
_runnable.run();
}
System.out.println("execution took " + (System.currentTimeMillis() - start) +" ms");
}
}
public static void main(String[] args) throws Exception {
new TimeoutTask(2000L, new Runnable() {
#Override
public void run() {
System.out.println("doing something ...");
try {
// pretend it's taking somewhat longer than it really does
Thread.sleep(100);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
}
}).start();
}
}
If this isn't an option, please narrow your requirements - or show some code.
I was looking for an ExecutorService that can interrupt all timed out Runnables executed by it, but found none. After a few hours I created one as below. This class can be modified to enhance robustness.
public class TimedExecutorService extends ThreadPoolExecutor {
long timeout;
public TimedExecutorService(int numThreads, long timeout, TimeUnit unit) {
super(numThreads, numThreads, 0L, TimeUnit.MILLISECONDS, new ArrayBlockingQueue<Runnable>(numThreads + 1));
this.timeout = unit.toMillis(timeout);
}
#Override
protected void beforeExecute(Thread thread, Runnable runnable) {
Thread interruptionThread = new Thread(new Runnable() {
#Override
public void run() {
try {
// Wait until timeout and interrupt this thread
Thread.sleep(timeout);
System.out.println("The runnable times out.");
thread.interrupt();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
interruptionThread.start();
}
}
Usage:
public static void main(String[] args) {
Runnable abcdRunnable = new Runnable() {
#Override
public void run() {
System.out.println("abcdRunnable started");
try {
Thread.sleep(20000);
} catch (InterruptedException e) {
// logger.info("The runnable times out.");
}
System.out.println("abcdRunnable ended");
}
};
Runnable xyzwRunnable = new Runnable() {
#Override
public void run() {
System.out.println("xyzwRunnable started");
try {
Thread.sleep(20000);
} catch (InterruptedException e) {
// logger.info("The runnable times out.");
}
System.out.println("xyzwRunnable ended");
}
};
int numThreads = 2, timeout = 5;
ExecutorService timedExecutor = new TimedExecutorService(numThreads, timeout, TimeUnit.SECONDS);
timedExecutor.execute(abcdRunnable);
timedExecutor.execute(xyzwRunnable);
timedExecutor.shutdown();
}
Now , l meet a issue like this. It happens to decode picture. The process of decode takes too much time that the screen keep black. l add a time controler: when the time is too long, then pop up from the current Thread.
The following is the diff:
ExecutorService executor = Executors.newSingleThreadExecutor();
Future<Bitmap> future = executor.submit(new Callable<Bitmap>() {
#Override
public Bitmap call() throws Exception {
Bitmap bitmap = decodeAndScaleBitmapFromStream(context, inputUri);// do some time consuming operation
return null;
}
});
try {
Bitmap result = future.get(1, TimeUnit.SECONDS);
} catch (TimeoutException e){
future.cancel(true);
}
executor.shutdown();
return (bitmap!= null);
I had the same problem. So i came up with a simple solution like this.
public class TimeoutBlock {
private final long timeoutMilliSeconds;
private long timeoutInteval=100;
public TimeoutBlock(long timeoutMilliSeconds){
this.timeoutMilliSeconds=timeoutMilliSeconds;
}
public void addBlock(Runnable runnable) throws Throwable{
long collectIntervals=0;
Thread timeoutWorker=new Thread(runnable);
timeoutWorker.start();
do{
if(collectIntervals>=this.timeoutMilliSeconds){
timeoutWorker.stop();
throw new Exception("<<<<<<<<<<****>>>>>>>>>>> Timeout Block Execution Time Exceeded In "+timeoutMilliSeconds+" Milli Seconds. Thread Block Terminated.");
}
collectIntervals+=timeoutInteval;
Thread.sleep(timeoutInteval);
}while(timeoutWorker.isAlive());
System.out.println("<<<<<<<<<<####>>>>>>>>>>> Timeout Block Executed Within "+collectIntervals+" Milli Seconds.");
}
/**
* #return the timeoutInteval
*/
public long getTimeoutInteval() {
return timeoutInteval;
}
/**
* #param timeoutInteval the timeoutInteval to set
*/
public void setTimeoutInteval(long timeoutInteval) {
this.timeoutInteval = timeoutInteval;
}
}
Guarantees that if block didn't execute within the time limit. the process will terminate and throws an exception.
example :
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
}