Name: rlT66838 Date: 04/10/2000


java version "1.3.0rc2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0rc2-Y)

An interrupted thread appears not to be able to produce output through
System.err and System.out. This remains the case while the 'interrupted' flag is
set. Once the 'interrupted' flag has been cleared (either by a call to
Thread.interrupted or to an 'interruptable' method such as Thread.sleep), the
thread produces output normally.

Below is a Java class that demonstrates the problem.'java InterruptBug yes' runs
a thread which is (immediately) interrupted. 'java InterruptBug no' runs a
thread which is not interrupted. In both cases the thread repeatedly (once every
second, for five seconds) checks and prints the outcome of 'isInterrupted()'.
After that, it does the same for 'interrupted()'.

The 'no' version will produce correct output during the full ten seconds.
However the 'yes' version will buffer its output during the first five or six
seconds. Then, after clearing the 'interrupted' flag, the buffered output is
printed, followed by the remaining output.

Output of the 'no version':

bash-2.00$ java InterruptBug no
not interrupting
isInterrupted: false
isInterrupted: false
isInterrupted: false
isInterrupted: false
isInterrupted: false
interrupted: false
interrupted: false
interrupted: false
interrupted: false
interrupted: false

Output of the 'yes' version:

bash-2.00$ java InterruptBug yes
interrupting
isInterrupted: true
isInterrupted: true
isInterrupted: true
isInterrupted: true
isInterrupted: true
interrupted: true
interrupted: false
interrupted: false
interrupted: false
interrupted: false

Note that the 'yes' output shown above is correct. However there is a delay,
which is incorrect.

public class InterruptBug implements Runnable
{
  public static void main (String[] args)
  {
     if (args.length != 1) {
       System.err.println ("Usage: InterruptBug [yes|no]");
       return;
     }
     boolean do_interrupt = "yes".equals (args [0]);

     Thread t = new Thread (new InterruptBug());
     t.start();
     if (do_interrupt) {
       System.out.println ("interrupting");
       t.interrupt();
     }
     else
       System.out.println ("not interrupting");
  }

  public void run()
  {
    // for five seconds, repeatedly check the 'interrupted' flag
    for (int j = 0; j < 5; j++) {
      sleep (1000);
      if (Thread.currentThread().isInterrupted())
        System.out.println ("isInterrupted: true");
      else
        System.out.println ("isInterrupted: false");
    }

    // for five seconds, repeatedly check and clear the 'interrupted' flag
    for (int j = 0; j < 5; j++) {
      sleep (1000);
      if (Thread.interrupted())
        System.out.println ("interrupted: true");
      else
        System.out.println ("interrupted: false");
    }
  }

  /** Sleep without using Thread.sleep. */
  private static void sleep (long millis)
  {
    long end_time = System.currentTimeMillis() + millis;
    while (System.currentTimeMillis() < end_time)
      ;
  }
}
(Review ID: 103479)
======================================================================

Name: yy116575 Date: 02/15/2001

Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0)
Java HotSpot(TM) Client VM (build 1.3.0, mixed mode)


Calling System.out.println clears the interrupted flag for the thread.

The following example code has the following output:

Before => true
After => false

public class junk {
  public static void main(String[] args) {
    try {
      Thread.currentThread().interrupt();
      boolean keepInterrupted = Thread.currentThread().isInterrupted();

      System.out.println(); // This blank line disappears.
      System.out.println("Before => " + keepInterrupted);
      System.out.println("After => " + Thread.currentThread().isInterrupted());

    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}
(Review ID: 117079)
======================================================================

In the first test case, if the output is flushed then it appears immediately
but that seems to clear the interrupted status:
> java InterruptBug yes
interrupting
isInterrupted: true
isInterrupted: false
isInterrupted: false
isInterrupted: false
isInterrupted: false
interrupted: false
interrupted: false
interrupted: false
interrupted: false
interrupted: false

This doesn't occur on Linux.

michael.mccloskey@eng 2001-04-03