Question

I have a program with 2 process java : processA and processB ( 2 process java.exe not 2 threads).
i use code block below from process A to invoke processB this code is wrapped in RunTask class below

public class RunTask implements Callable<Object> {

private String runParams;

public String getRunParams() {
    return runParams;
}

public void setRunParams(String runParams) {
    this.runParams = runParams;
}

@Override
public Object call() throws Exception {
    try {
        //System.out.println("run:" + runParams);
        Process procB = Runtime.getRuntime().exec("java -jar processB.jar);
        DataInputStream ls_in = new DataInputStream(procB.getInputStream());
        String ls_str;
        while ((ls_str = ls_in.readLine()) != null) {
            System.out.println(ls_str);
        }

    } catch (Exception exp) {
        exp.printStackTrace();
    }
    return null;
}
}

and Main class i use executor

   ExecutorService eservice = Executors.newSingleThreadExecutor();
        while (1 == 1) {
            String stringParams = getFilesNeedToImportAsString();
            if (stringParams.trim().isEmpty()) {
                long l1 = System.currentTimeMillis() - l;
                System.out.println("all time" + l1 / 1000);
                System.exit(100);
            }
            RunTask runTask = new RunTask();
            runTask.setRunParams(SystemInfo.RUN_COMMAND + stringParams);
            Future<Object> objectFuture = eservice.submit(runTask);
            while (!objectFuture.isDone()) {
                System.out.println("waiting the task running");
                Thread.sleep(500);
            }
        }

But when an exception occurred on processB both processes (processA,processB) seem be halted this is code run on processB

public Object call() {
    try {
        MutationResult result = mutator.execute();
        return "ok";
    } catch (Exception exp) {
        exp.printStackTrace();
        System.out.println("error on " + Thread.currentThread().getName() + "failed begin retry " + (++retryCount));
        call();
        System.out.println(retryCount + " completed");
        return "ok";
    }

}

if i run processB stand alone (by command line) it’s never happen, or when this problem occured i use taskmanager to kill proceesA (callee), processB continue to run

Please any one give me the solution for this problem !!

Answer 1

You wait on objectFuture isDone method to complete. According to the documentation:

isDone: Returns true if this task completed. Completion may be due to
normal termination, an exception, or cancellation — in all of these
cases, this method will return true

Looking at the code in processB when an exception occurs you execute call() again recursively. I understand that you do this as a error retry mechanism but this is a really bad idea for two main reasons:
– If the exception persists you will end up getting a StackOverflowException.
– None of the conditions for isDone will be met.

A better alternative will be defining a maximum number of retries and try executing mutator.execute(). If the error persists then throw and exception and finish execution.

Another option would be to wait to processB to finish for a maximum time after which you cancel the execution of the task by calling objectFuture.cancel(true).

A couple of comments on processA: On RunTask you don’t use runParams which seem to be some files that need to be imported as string. Also, you use readLine() on DataInputStream which is a deprecated method. Instead use an InputStream (e.g. BufferedInputStream) wrapped in an InputStreamReader and then wrapped in a BufferedReader – then call readLine() on the BufferedReader.