I have multiple threads calling an API. API opens a socket which doesn't have timeout set on it. However, I have timeout set on future.get()..If socket is kept open forever does future's timeout come in action and get out of the processing of task which calls an API ?
The Future.get will throw a TimeoutException when the timeout expires.
Yet, the underlying task will keep executing unless you have a way to interrupt it. It can be for instance by closing the socket if you have access to it or by any mechanism that the API provides.
You can try to interrupt the execution but it is up to code to catch the interruption (via Thread.interrupted()) so it may have no effect depending on the underlying task implementation:
try {
Future<R> future = // ...
} catch (TimeoutException e) {
// ...
future.cancel(true); // try to interrupt
}
Related
I have a java-program which runs on a schedule and fetches some data from external sources via RFC calls. The RFC calls are threaded and shall be canceled after 60 seconds. This is how I do it:
Future<String> future = executor.submit(new MyCallable());
try {
future.get(60, TimeUnit.SECONDS);
} catch (TimeoutException e) {
future.cancel(true);
}
This worked for a long time until I came accross a situation, where the external RFC call became stuck and future.cancel(true) was unable to interrupt the thread-execution. So my java-program never finished and continued running until I manually canceled the corresponding process within the external system.
My question now is, how can one guarantee the code to finish in any situation? I saw that stopping the thread is depreciated.
Would it be a good idea to do sth like this?
try {
future.get(60, TimeUnit.SECONDS);
} catch (TimeoutException e) {
future.cancel(true);
if(!future.isDone()){
System.exit(1);
}
}
Thanks for any ideas on this.
Cheers, Jooo
I believe that there's no way in Java to just kill off a thread if during execution not implemented InterruptedException . If the thread is executing, it just sets a flag and it's up to the thread to notice it. if the thread is waiting or sleeping, it will throw an InterruptedException.
No need to check after every line, of course, but methods which can take a long time to execute are responsible for properly handling interrupts
kill the process in which the thread is running. (E.g., call System.exit(int).)
I am trying to use a Third Party Internal Library which is processing a given request. Unfortunately it is synchronous in nature. Also I have no control on the code for the same. Basically it is a function call. This function seems to a bit erratic in behavior. Sometimes this function takes 10 ms to complete processing and sometimes it takes up to 300 secs to process the request.
Can you suggest me a way to write a wrapper around this function so that it would throw an interrupted exception if the function does not complete processing with x ms/secs. I can live with not having the results and continue processing, but cannot tolerate a 3 min delay.
PS: This function internally sends an update to another system using JMS and waits for that system to respond and sends apart from some other calculations.
Can you suggest me a way to write a wrapper around this function so that it would throw an interrupted exception if the function does not complete processing with x ms/secs.
This is not possible. InterruptException only gets thrown by specific methods. You can certainly call thread.stop() but this is deprecated and not recommended for a number of reasons.
A better alternative would be for your code to wait for the response for a certain amount of time and just abandon the call if doesn't work. For example, you could submit a Callable to a thread pool that actually makes the call to the "Third Party Internal Library". Then your main code would do a future.get(...) with a specific timeout.
// allows 5 JMS calls concurrently, change as necessary or used newCachedThreadPool()
ExecutorService threadPool = Executors.newFixedThreadPool(5);
...
// submit the call to be made in the background by thread-pool
Future<Response> future = threadPool.submit(new Callable<Response>() {
public Response call() {
// this damn call can take 3 to 3000ms to complete dammit
return thirdPartyInternalLibrary.makeJmsRequest();
}
});
// wait for some max amount of time
Response response = null;
try {
response = future.get(TimeUnit.MILLISECONDS, 100);
} catch (TimeoutException te) {
// log that it timed out and continue or throw an exception
}
The problem with this method is that you might spawn a whole bunch of threads waiting for the library to respond to the remote JMS query that you would not have a lot of control over.
No easy solution.
This will throw a TimeoutException if the lambda doesn't finish in the time allotted:
CompletableFuture.supplyAsync(() -> yourCall()).get(1, TimeUnit.SECONDS)
Being that this is 3rd party you cannot modify the code. As such you will need to do two things
Launch the execution in a new thread.
Wait for execution in current thread, with timeout.
One possible way would be to use a Semaphore.
final Semaphore semaphore = new Semaphore(0);
Thread t = new Thread(new Runnable() {
#Override
public void run() {
// do work
semaphore.release();
}
});
t.start();
try {
semaphore.tryAcquire(1, TimeUnit.SECONDS); // Whatever your timeout is
} catch (InterruptedException e) {
// handle cleanup
}
The above method is gross, I would suggest instead updateing your desing to use a dedicated worker queue or RxJava with a timeout if possible.
I am having difficulty trying to correctly program my application in the way I want it to behave.
Currently, my application (as a Java Servlet) will query the database for a list of items to process. For every item in the list, it will submit an HTTP Post request. I am trying to create a way where I can stop this processing (and even terminate the HTTP Post request in progress) if the user requests. There can be simultaneous threads that are separately processing different queries. Right now, I will stop processing in all threads.
My current attempt involves implementing the database query and HTTP Post in a Callable class. Then I submit the Callable class via the Executor Service to get a Future object.
However, in order properly to stop the processing, I need to abort the HTTP Post and close the database's Connection, Statement and ResultSet - because the Future.cancel() will not do this for me. How can I do this when I call cancel() on the Future object? Do I have to store a List of Arrays that contains the Future object, HttpPost, Connection, Statement, and ResultSet? This seems overkill - surely there must be a better way?
Here is some code I have right now that only aborts the HttpPost (and not any database objects).
private static final ExecutorService pool = Executors.newFixedThreadPool(10);
public static Future<HttpClient> upload(final String url) {
CallableTask ctask = new CallableTask();
ctask.setFile(largeFile);
ctask.setUrl(url);
Future<HttpClient> f = pool.submit(ctask); //This will create an HttpPost that posts 'largefile' to the 'url'
linklist.add(new tuple<Future<HttpClient>, HttpPost>(f, ctask.getPost())); //storing the objects for when I cancel later
return f;
}
//This method cancels all running Future tasks and aborts any POSTs in progress
public static void cancelAll() {
System.out.println("Checking status...");
for (tuple<Future<HttpClient>, HttpPost> t : linklist) {
Future<HttpClient> f = t.getFuture();
HttpPost post = t.getPost();
if (f.isDone()) {
System.out.println("Task is done!");
} else {
if (f.isCancelled()) {
System.out.println("Task was cancelled!");
} else {
while (!f.isDone()) {
f.cancel(true);
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("!Aborting Post!");
try {
post.abort();
} catch (Exception ex) {
System.out.println("Aborted Post, swallowing exception: ");
ex.printStackTrace();
}
}
}
}
}
}
Is there an easier way or a better design? Right now I terminate all processing threads - in the future, I would like to terminate individual threads.
I think keeping a list of all the resources to be closed is not the best approach. In your current code, it seems that the HTTP request is initiated by the CallableTask but the closing is done by somebody else. Closing resources is the responsibility of the one who opened it, in my opinion.
I would let CallableTask to initiate the HTTP request, connect to database and do it's stuff and, when it is finished or aborted, it should close everything it opened. This way you have to keep track only the Future instances representing your currently running tasks.
I think your approach is correct. You would need to handle the rollback yourself when you are canceling the thread
cancel() just calls interrupt() for already executing thread. Have a look here
http://docs.oracle.com/javase/tutorial/essential/concurrency/interrupt.html:
As it says
An interrupt is an indication to a thread that it should stop what it
is doing and do something else. It's up to the programmer to decide
exactly how a thread responds to an interrupt, but it is very common
for the thread to terminate.
Interrupted thread would throw InterruptedException
when a thread is waiting, sleeping, or otherwise paused for a long
time and another thread interrupts it using the interrupt() method in
class Thread.
So you need to explicitly code for scenarios such as you mentioned in executing thread where there is a possible interruption.
i have a thread that is connecting to a url to obtaining some data.
Sometimes the method httpConnection.connect(); taked too munch time to get the response, and i want to limit the loading dialog of this connection thread to 5 seg.
I tryed adding timeouts into the code, but it doesn't work!!
URL formattedUrl = new URL(url);
URLConnection connection = formattedUrl.openConnection();
connection.setConnectTimeout(5000);
connection.setReadTimeout(5000);
HttpURLConnection httpConnection = (HttpURLConnection) connection;
httpConnection.setAllowUserInteraction(false);
httpConnection.setInstanceFollowRedirects(true);
httpConnection.setRequestMethod("GET");
httpConnection.setConnectTimeout(5000);
httpConnection.setReadTimeout(5000);
httpConnection.connect();
So, i must stop the connect method and the thread when 5000 seconds have passed or when the used has pressed the back key on the phone.
How can this be achieved? i can't find info about doing this work in android with a url connection thread.
thanks
The timeout settings on URLConnection are not sufficient to provide the timeout control desired. The reason being is:
setConnectTimeout() sets the timeout for just establishing a connection with the server. So, a timeout will only be triggered if when opening the connection, the connection can not be established in the prescribed amount of time.
setReadTimeount() sets the timeout for reading available data. For this, a timeout will only be triggered if any, single read operation blocks for longer than the set amount of time. So, it is quite possible even on a slow connection that each read operation never approaches the timeout threshold but, the total amount of time to read all the data is quite lengthly.
One solution to apply a timeout to the entire read unit of work, is to use the concurrency capabilities found in Java 5 and beyond. In particular, the use of an ExecutorService and Future should be sufficient.
Runnable task = new Runnable() {
public void run() {
// original code to read data from a URL
}
};
ExecutorService executor = Executors.newSingleThreadExecutor(); // or any other implementation
Future<?> future = executor.submit(task);
try {
future.get(5, TimeUnit.SECONDS); // wait 5 seconds for task to complete
// success
} catch (TimeoutException ex) {
// handle timeout
} finally {
executor.shutdownNow(); // cleanup
}
Brent Worden's answer is on the right track. But there is a problem with his solution. If the task timeout kicks in, the thread that called future.get will get an exception as expected. However, the worker thread that was executing the Runnable.run() method may still be stuck waiting for the connect or read to complete.
Solving this is difficult. As far as I'm aware, the only reliable way to unjam a thread that is waiting on a socket connect or socket stream read or write is to call close() on the Socket object. And the problem with using that approach (here) is that the standard HttpUrlConnection object doesn't expose the Socket object.
My recommendation would be to use the Apache Http client libraries. This question explains how to abort a request if you use HttpClient: Cancel an HttpClient request
You only need to invoke the URLConnection.setConnectTimeout(millis) to achieve what you asking. If the specified timeout expires a SocketTimeoutException is thrown.
try {
HttpURLConnection con = (HttpURLConnection) new URL(url).openConnection();
con.setConnectTimeout(5000); //set timeout to 5 seconds
} catch (java.net.SocketTimeoutException e) {
//DO SOMETHING
} catch (java.io.IOException e) {
//DO SOMETHING
}
It's worth noting that it says the following:
Some non-standard implmentation of this method may ignore the
specified timeout. To see the connect timeout set, please call
getConnectTimeout().
You can't, the process which the thread belongs to will end if you stop the thread.
I have a server thread with this code:
public void run() {
try {
ServerSocket server;
EneaLog.printLog("Server is running.");
server = new ServerSocket(this.portnumber);
while (true) {
new EneaServerConnection(server.accept(), this.project,stopped).start();
if (stopped) {
EneaLog.printLog("Server safe-shutdown completed.");
EneaLog.printLog("Hi!");
server.close();
return;
}
}
} catch (IOException ex) {
Logger.getLogger(EneaServer.class.getName()).log(Level.SEVERE, null, ex);
project.getExceptionHandler().handler(ex);
}
}
and a shutdown method like this:
public void shutdown() {
EneaLog.printLog("Server shutdown NOW!");
stopped = true;
}
I want that shutdown can unblock thread that are waiting on server.accept() otherwise I must wait for connection before server shutdown.
I can't do server.close() in shutdown() because I must signal to registered client that server is coming down.
Any ideas?
I try to design my code so that it can be "shutdown" with an interrupt. Mainly, this is because the Executor framework in Java's concurrency package uses interrupt to cancel running tasks. Also, the "shutdown" task doesn't have to know any internals of the task being killed.
However, a call to accept will not respond to an interrupt unless it is created from a ServerSocketChannel. A server created with a ServerSocket constructor will ignore interrupts, and I haven't found a way to reconfigure this.
If you can't change the code that creates the server, arrange for another thread to call close on the server socket. This will also raise an exception in thread blocked on accept, regardless of the method used to create the server socket.
This turns out to be a really big pain when using SSL. A JSSE socket is not created from an InterruptibleChannel, and won't respond to a simple interrupt on the thread.
I just noticed that the question says that the server can't be closed without notifying the client. Successfully interrupting a socket results in its closure.
On a call to accept this shouldn't be a problem, since the client is not connected if the server socket is blocked in accept. That should only be an issue for Socket instances, that represent current connections.
If that doesn't satisfy the notification requirements, a rework to use NIO's ServerSocketChannel in non-blocking mode may be necessary.
You should be able to close the socket from another thread.
Neither interrupt (that's dependent on interrupt points in the same way cancellation is dependent on cancellation points) nor close will do it (accept does not responsed to closing its file descriptor). You'll have to communicate with the accept (try sendto, with a shutdown notification) to notify it to not continue accepting. At least this is the case on linux; don't know what it's like on other platforms.
I've been faced to the same problem. My working solutions consists into closing the ServerSocket object (serverSocket.close()) ; doing this will cause the accept() method to throw a SocketException, which is what you want to do.
Vincent
Have you tried Thread.interrupt() ?
If this thread is blocked in an I/O
operation upon an interruptible
channel then the channel will be
closed, the thread's interrupt status
will be set, and the thread will
receive a ClosedByInterruptException.
If this thread is blocked in a
Selector then the thread's interrupt
status will be set and it will return
immediately from the selection
operation, possibly with a non-zero
value, just as if the selector's
wakeup method were invoked.