Saxon

Thanks for the clear test case.

When the iterator is closed, the idea is that the whole chain of underlying iterators should be closed, and eventually the iterator that reads from the provider thread signals the provider thread to close. But within the chain of underlying iterators is a ContextMappingIterator, which supports a construct such as A!B where there are two nested iterators, one for A and one for B. The iterator for A is being closed, but that for B is not, and it is the iterator for B that is connected to the provider thread.

Fixed by a patch to ContextMappingIterator.close().

Note: MappingIterator gets this right, it's only ContextMappingIterator that gets it wrong.

The same problem is present in 9.6 and I have applied the patch there also.

Bug fix applied in the Saxon 9.7.0.2 maintenance release

Thank you for taking care of this.

Meanwhile I have retested with Saxon 9.7.0.2. Though it does not happen in each iteration any more, there is still a chance of some thread being left over. The number varies in repeated executions of the test.

I have modified my test (now ThreadCountTest2) to show the stack traces of the left-over threads, and they all look the same:

number of threads increased from 6 to 8
  Thread-1791
    sun.misc.Unsafe.park(Native Method)
    java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    java.util.concurrent.ArrayBlockingQueue.put(ArrayBlockingQueue.java:353)
    com.saxonica.ee.stream.PushToPull$QueueWriter.write(PushToPull.java:63)
    com.saxonica.ee.stream.PushToPull$Provider.run(PushToPull.java:95)
    java.lang.Thread.run(Thread.java:745)
  Thread-1793
    sun.misc.Unsafe.park(Native Method)
    java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    java.util.concurrent.ArrayBlockingQueue.put(ArrayBlockingQueue.java:353)
    com.saxonica.ee.stream.PushToPull$QueueWriter.write(PushToPull.java:63)
    com.saxonica.ee.stream.PushToPull$Provider.run(PushToPull.java:95)
    java.lang.Thread.run(Thread.java:745)