I have some method with render() name and I want to call it asynchronously and set timeout to that async call.
when timeout will finish I need to stop async call.
I tried such code but it doesn't stop async call after timeout
Future<File> fileFuture = null;
try {
fileFuture = executor.getThreadPoolExecutor()
.submit(() -> render());
return fileFuture.get(10,TimeUnit.SECONDS);
} catch (TimeoutException e) {
fileFuture.cancel(true);
throw new MyTimeOutException(e);
}
}
How can I do this in Java?
And also It will be better that it will be done by Java java concurrent package.
And I want to add that I use Spring Boot and please write if there is any solution by Spring.
When you call fileFuture.cancel(true), Java will send an interrupt to the thread that is running render(). However, this by itself does not automatically stop the render task. You need to check for the interrupt from within render() and stop if an interrupt is detected.
Without looking at the implementation for render(), it's hard to say where exactly within the method you should check for it, but as a rule you should check for interrupts periodically during a long-running task. Here's an example:
public void render() {
for (int i = 0; i < inputs.length; i++) { // some long running task
heavyCrunch(inputs[i]);
if (Thread.interrupted()) { // returns true if an interrupt has been received
// We've been interrupted: no more crunching.
return;
}
}
}
You can read the full Oracle guide on interrupts here
Note that even with this solution, your render() method won't stop immediately when you call cancel() - there will be a lag between when cancel() is called and render() checks for interrupts. The more frequently you check for interrupts, the smaller this lag will be.
Related
inside a Spring web application I have a scheduled task that is called every five minutes.
#Scheduled(fixedDelay = 300000)
public void importDataTask()
{
importData(); //db calls, file manipulations, etc..
}
Usually the task runs smoothly for days, but sometimes happens that the example method importaData()will not terminate, so importDataTask()will not be called again and everything will be blocked until I restart the application.
The question is: is there a feasibile method to be sure that a method will not be indefinitely blocked (waybe waiting for a resource, or something else)?
The question is: is there a feasibile method to be sure that a method
will not be indefinitely blocked (waybe waiting for a resource, or
something else)?
If the scheduling cannot be planned at a precise regular interval, you should maybe not use a fixed delay but use two conditions : delay + last execution done.
You could schedule a task which checks if the two conditions are met and if it the case, you run the important processing. Otherwise, it waits for the next schedule.
In this way, you should not be blocked. You could wait for some time if the task exceeds the fixed delay. If it is a problem because the fixed delay is often exceeded, you should probably not use a fixed delay or so you should increase sensitively it in order that it is less common.
Here an example (writing without editor. Sorry if any mistake) :
private boolean isLastImportDataTaskFinished;
#Scheduled(fixedDelay = 300000)
public void importDataTaskManager(){
if (isLastImportDataTaskFinished()){
new Thread(new ImportantDataProcessing())).start();
}
else{
// log the problem if you want
}
}
private isLastImportDataTaskFinished(){
// to retrieve this information, you can do as you want : use a variable
// in this class or a data in database,file...
// here a simple implementation
return isLastImportDataTaskFinished;
}
Runnable class :
public class ImportantDataProcessing implements Runnable{
public void run(){
importData(); //db calls, file manipulations, etc..
}
}
Comment:
But if I run it as a thread how can I kill it if I find it's exceeding
the time limit since I don't have any reference to it (in the idea of
using a second task to determine the stuck state)?
You can use an ExecutorService (you have a question about it here : How to timeout a thread).
Here a very simple example :
ExecutorService executor = Executors.newSingleThreadExecutor();
Future future = executor.submit(new ImportantDataProcessing());
try {
future.get(100, TimeUnit.SECONDS);
}
catch (InterruptedException e) {
e.printStackTrace();
}
catch (ExecutionException e) {
e.printStackTrace();
}
catch (TimeoutException e) {
// the timeout to handle but other exceptions should be handled :)
e.printStackTrace();
}
executor.shutdown();
If interesting information may be returned by ImportantDataProcessing processing , you can use a task instead of a runnable instance to type the future.
Firstly, sure. There are many feasibile methods to remind you if the process is blocked, such as log/message/email which embed in you code.
Secondly, it is decided by if you want it block or not. If block is not you intention, new thread or timeout may be you choice.
I create a Thread like the following code. This Thread will send the POST request.(The code is not yet written , so I didn't post the detail code of Thread )
final Runnable Update_Value = new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
**// It will send the POST request to the Server**
}
};
I use the new Thread(Update_Value).start(); to run the Thread.
And I use new Thread(Update_Value).interrupt(); to interrupt the Thread.
1. If I use new Thread(Update_Value).start(); to run the Thread.
2 How to interrupt the Thread when I using new Thread(Update_Value).start(); ?
3 Is the thread close when App close if I didn't close it ?
Sorry about my English...Thanks in advance.
If you use new Thread each time, the two calls create two different threads; they don't act on the same thread.
The interrupt() method does not stop the thread. Rather, it tells the thread to take a look at any interrupt flags that may also have been set, such as a shutdown flag. The thread itself must contain code to check for interrupts and to check for flags such as shutdown flags.
interrupt method is used to send an interrupt signal to a running thread. Calling on a new thread does not make sense.
To properly handle the interrupt signal, your thread code should catch InterruptedException. Something like this:
try {
// do thread task
} catch (InterruptedException e) {
// interrupted: if required do something on interrupt or simply return
return;
}
I am using the Java ExecutorService framework to submit callable tasks for execution.
These tasks communicate with a web service and a web service timeout of 5 mins is applied.
However I've seen that in some cases the timeout is being ignored and thread 'hangs' on an API call - hence, I want to cancel all the tasks that take longer than say, 5 mins.
Currently, I have a list of futures and I iterate through them and call future.get until all tasks are complete. Now, I've seen that the future.get overloaded method takes a timeout and throws a timeout when the task doesnt complete in that window. So I thought of an approach where I do a future.get() with timeout and in case of TimeoutException I do a future.cancel(true) to make sure that this task is interrupted.
My main questions
1. Is the get with a timeout the best way to solve this issue?
2. Is there the possibility that I'm waiting with the get call on a task that hasnt yet been placed on the thread pool(isnt an active worker). In that case I may be terminating a thread that, when it starts may actually complete within the required time limit?
Any suggestions would be deeply appreciated.
Is the get with a timeout the best way to solve this issue?
This will not suffice. For instance, if your task is not designed to response to interruption, it will keep on running or be just blocked
Is there the possibility that I'm waiting with the get call on a task that hasnt yet been placed on the thread pool(isnt an active worker). In that case I may be terminating a thread that, when it starts may actually complete within the required time limit?
Yes, You might end up cancelling as task which is never scheduled to run if your thread-pool is not configured properly
Following code snippet could be one of the way you can make your task responsive to interruption when your task contains Non-interruptible Blocking. Also it does not cancel the task which are not scheduled to run. The idea here is to override interrupt method and close running tasks by say closing sockets, database connections etc. This code is not perfect and you need to make changes as per requirements, handle exceptions etc.
class LongRunningTask extends Thread {
private Socket socket;
private volatile AtomicBoolean atomicBoolean;
public LongRunningTask() {
atomicBoolean = new AtomicBoolean(false);
}
#Override
public void interrupt() {
try {
//clean up any resources, close connections etc.
socket.close();
} catch(Throwable e) {
} finally {
atomicBoolean.compareAndSet(true, false);
//set the interupt status of executing thread.
super.interrupt();
}
}
public boolean isRunning() {
return atomicBoolean.get();
}
#Override
public void run() {
atomicBoolean.compareAndSet(false, true);
//any long running task that might hang..for instance
try {
socket = new Socket("0.0.0.0", 5000);
socket.getInputStream().read();
} catch (UnknownHostException e) {
} catch (IOException e) {
} finally {
}
}
}
//your task caller thread
//map of futures and tasks
Map<Future, LongRunningTask> map = new HashMap<Future, LongRunningTask>();
ArrayList<Future> list = new ArrayList<Future>();
int noOfSubmittedTasks = 0;
for(int i = 0; i < 6; i++) {
LongRunningTask task = new LongRunningTask();
Future f = execService.submit(task);
map.put(f, task);
list.add(f);
noOfSubmittedTasks++;
}
while(noOfSubmittedTasks > 0) {
for(int i=0;i < list.size();i++) {
Future f = list.get(i);
LongRunningTask task = map.get(f);
if (task.isRunning()) {
/*
* This ensures that you process only those tasks which are run once
*/
try {
f.get(5, TimeUnit.MINUTES);
noOfSubmittedTasks--;
} catch (InterruptedException e) {
} catch (ExecutionException e) {
} catch (TimeoutException e) {
//this will call the overridden interrupt method
f.cancel(true);
noOfSubmittedTasks--;
}
}
}
}
execService.shutdown();
Is the get with a timeout the best way to solve this issue?
Yes it is perfectly fine to get(timeout) on a Future object, if the task that the future points to is already executed it will return immediately. If the task is yet to be executed or is being executed then it will wait until timeout and is a good practice.
Is there the possibility that I'm waiting with the get call on a task
that hasnt yet been placed on the thread pool(isnt an active worker)
You get Future object only when you place a task on the thread pool so it is not possible to call get() on a task without placing it on thread pool. Yes there is a possibility that the task has not yet been taken by a free worker.
The approach that you are talking about is ok. But most importantly before setting a threshold on the timeout you need to know what is the perfect value of thread pool size and timiout for your environment. Do a stress testing which will reveal whether the no of worker threads that you configured as part of Threadpool is fine or not. And this may even reduce the timeout value. So this test is most important i feel.
Timeout on get is perfectly fine but you should add to cancel the task if it throws TimeoutException. And if you do the above test properly and set your thread pool size and timeout value to ideal than you may not even need to cancel tasks externally (but you can have this as backup). And yes sometimes in canceling a task you may end up canceling a task which is not yet picked up by the Executor.
You can of course cancel a Task by using
task.cancel(true)
It is perfectly legal. But this will interrupt the thread if it is "RUNNING".
If the thread is waiting to acquire an intrinsic lock then the "interruption" request has no effect other than setting the thread's interrupted status. In this case you cannot do anything to stop it. For the interruption to happen, the thread should come out from the "blocked" state by acquiring the lock it was waiting for (which may take more than 5 mins). This is a limitation of using "intrinsic locking".
However you can use explicit lock classes to solve this problem. You can use "lockInterruptibly" method of the "Lock" interface to achieve this. "lockInterruptibly" will allow the thread to try to acquire a lock while remaining responsive to the interruption. Here is a small example to achieve that:
public void workWithExplicitLock()throws InterruptedException{
Lock lock = new ReentrantLock();
lock.lockInterruptibly()();
try {
// work with shared object state
} finally {
lock.unlock();
}
}
I have tried many different ways to immediately stop a task which is started using an ExecutorService, with no luck.
Future<Void> future = executorService.submit(new Callable<Void>(
public Void call () {
... do many other things here..
if(Thread.currentThread.isInterrupted()) {
return null;
}
... do many other things here..
if(Thread.currentThread.isInterrupted()) {
return null;
}
}
));
if(flag) { // may be true and directly cancel the task
future.cancel(true);
}
Sometimes I need to cancel the task immediately after it is started, you may be curious why I want to do this, well you may imagine a senario that a user accidentally hits the "Download" button to start a "Download Task" and he immediately wants to cancel the action because it was just an accidental click.
The problem is that after calling future.cancel(true), the task is not stopped and Thread.currentThread.isInterrupted() still returns false and I have no way to know the task was stopped from inside the call() method.
I am thinking of setting a flag like cancelled=true after calling future.cancel(true) and checking that flag constantly in the call() method, I think this is a hack and the code could be very ugly because the user can start many tasks at the same moment.
Is there a more elegant way of achieving what I want?
EDIT:
This really drives me mad. I have spent almost a day on this problem now. I will try to explain a little bit more for the problem I am facing.
I do the following to start 5 tasks, each task will start 5 threads to download a file. and then I stop all 5 tasks immediately. For all of the method calls below, i start a thread(ExecutorService.submit(task)) to make it asynchronous as you can tell from the suffixes of the methods.
int t1 = startTaskAysnc(task1);
int t2 = startTaskAysnc(task2);
int t3 = startTaskAysnc(task3);
int t4 = startTaskAysnc(task4);
int t5 = startTaskAysnc(task5);
int stopTaskAysnc(t1);
int stopTaskAysnc(t2);
int stopTaskAysnc(t3);
int stopTaskAysnc(t4);
int stopTaskAysnc(t5);
in startTaskAysnc(), I simply initiate a socket connection to remote server to get the size of the file(and this certainly is gonna take some time), after successfully getting the fileSize, I will start 5 threads to download different parts of the file. like the following(the code is simplified to make it more easy to follow):
public void startTaskAsync(DownloadTask task) {
Future<Void> future = executorService.submit(new Callable<Void>(
public Void call () {
// this is a synchronous call
int fileSize = getFileSize();
System.out.println(Thread.currentThread.isInterrupted());
....
Future<Void> futures = new Future<Void>[5];
for (int i = 0; i < futures.length; ++i) {
futures[i] = executorService.submit(new Callable<Void>(){...});
}
for (int i = 0; i < futures.length; ++i) {
futures[i].get(); // wait for it to complete
}
}
));
synchronized (mTaskMap) {
mTaskMap.put(task.getId(), future);
}
}
public void stopTaskAysnc(int taskId) {
executorService.execute(new Runnable(){
Future<Void> future = mTaskMap.get(taskId);
future.cancel(true);
});
}
I noticed a weird behavior that after I called stopTaskAsync() for all 5 tasks, there would always be at least one task that got stopped(i.e. Thread.currentThread.isInterrupted() return true), and the other 4 tasks kept running.
And I have tried your suggestions by setting an UncaughtExceptionHandler, but nothing comes out from that.
EDIT:
The problem was solved in this link: Can't stop a task which is started using ExecutorService
Well, the javadoc of Future.cancel(boolean) says that:
If the task has already started, then the mayInterruptIfRunning
parameter determines whether the thread executing this task should be
interrupted in an attempt to stop the task.
so it's quite certain that the thread that executes the task is interrupted. What could have happened is that one of the
... do many other things here..
is accidentally clearing the Thread's interrupted status without performing the desired
handling. If you'll put a breakpoint in Thread.interrupt() you might catch the criminal.
Another option I can think of is that the task terminates before capturing the interrupt, either because it's completed or thrown some uncaught exception. Call Future.get() to determine that. Anyway, as asdasd mentioned, it is a good practice to set an UncaughtExceptionHandler.
What you're doing is very dangerous: you're using a thread pool to execute tasks (which I'll call downloaders), and the same thread pool to execute tasks which
wait for the downloaders to finish (which I'll call controllers)
or ask the controllers to stop
This means that if the core number of threads is reached after the controller has started, the downloaders will be put in the queue of the thread pool, and the controller thread will never finish. Similarly, if the core number of threads is reached when you execute the cancelling task, this cancelling task will be put in the queue, and won't execute until some other task is finished.
You should probably use a thread pool for downloaders, another one for controllers, and the current thread to cancel the controllers.
I think you'll find solution here. The main point is that cancel method raises InterruptedException. Please check if your thread is still running after cancellation? Are you sure that you didn't try to interrupt finished thread? Are you sure that your thread didn't fail with any other Exception? Try to set up UncaughtExceptionHandler.
I am running a thread whose main action is to call on a proxy using a blocking function , and wait for it to give it something.
I've used the known pattern of a volatile boolean and the Interruption , but I'm not sure it will work: When I tried to add a catch block for InterruptedException , I get the error:
Unreachable catch block for InterruptedException. This exception is never thrown from the try statement body
So if I'm never going to get anInterruptedException, this means I'll never get out of the blocking action - thus will never stop.
I'm a bit puzzled. Any idea?
public void run() {
Proxy proxy = ProxyFactory.generateProxy();
Source source;
while (!isStopped) {
try {
source = proxy.getPendingSources();
scheduleSource(source);
} catch (Exception e) {
log.error("UnExpected Exception caught while running",e);
}
}
}
public void stop() {
this.isStopped = true;
Thread.currentThread().interrupt();
}
First, you don't really need a separate flag (if you do, use an AtomicBoolean), just check Thread.currentThread().isInterrupted() as your while condition.
Second, your stop method won't work because it won't interrupt the correct thread. If another thread calls stop, the code uses Thread.currentThread() which means the calling thread will be interrupted, not the running one.
Finally, what is the blocking method? Is it scheduleSource()? If that method doesn't throw InterruptedException, you won't be able to catch it.
Try the following:
private final AtomicReference<Thread> currentThread = new AtomicReference<Thread>();
public void run() {
Proxy proxy = ProxyFactory.generateProxy();
Source source;
currentThread.set(Thread.currentThread());
while (!Thread.currentThread().isInterrupted()) {
try {
source = proxy.getPendingSources();
scheduleSource(source);
} catch (Exception e) {
log.error("UnExpected Exception caught while running", e);
}
}
}
public void stop() {
currentThread.get().interrupt();
}
Only a few, well-defined "blocking methods" are interruptible. If a thread is interrupted, a flag is set, but nothing else will happen until the thread reaches one of these well-defined interruption points.
For example, read() and write() calls are interruptible if they are invoked on streams created with a InterruptibleChannel. If a Socket is used as the starting point, calling interrupt() on a Thread blocked in the read has no effect. Note that if a blocking I/O operation is interrupted successfully, the underlying channel is closed.
Another large class of interruptible operations are those thrown by various blocking operations on classes in the java.util.concurrent packages. Of course, the original wait() method is interruptible as well.
Blocking methods can be identified by looking for a throws InterruptedException in their method signatures. They should be well-documented too, to describe any side-effects of interruption.
You can write an interruptible method of your own, but it has to be composed of interruptible lower-level operations itself.
ok, people, don't kill me over this.
I experimented with Thread.stop() for fun, to kick thread out of a blocking action, catch ThreadDeath, keep target thread alive, and move on.
It seems working. The world isn't ending. But I'm just saying. You are responsible for you own doing. Why am I rapping?
You stop method is calling interrupt on the wrong thread. Thread.currentThread() is the thread that is interrupting, not being interrupted.
How are you calling stop from the executing thread?
If you call stop() from another thread, you'll kill it, not the thread running in the try/catch block.