Code Review 7021010: java/lang/Thread/ThreadStateTest.java fails intermittently

[David Holmes]

Sorry for the delay on this ...

I concur with Mandy that using arrive() the thread must always be 
RUNNABLE or the expected next state. Hence the new check is ok.

With the new synchronization (and perhaps even the old) it seems to me 
that here:

         private void setState(int newState) {
             switch (state) {
                 case BLOCKED:
                     while (state == BLOCKED) {
                         goSleep(20);
                     }
                     state = newState;
                     break;

the sleep loop is unnecessary as after setting the new state the main 
thread will call arriveAndAwaitAdvance.

Also here:

                 try {
                        Thread.sleep(1000000);
                  } catch (InterruptedException e) {
                        // finish sleeping
                        interrupted();
                  }

the interrupted() call is redundant as the interrupt state is already 
cleared when the IE is thrown.

Cheers,
David


David Holmes said the following on 06/22/11 20:05:
> Mandy,
> 
> I need to study the test in more detail to see exactly how the thread is 
> supposed to change state and in what order. I'm not yet convinced that 
> arrive() in place of arriveAndAwaitAdvance() doesn't introduce races.
> 
> David
> 
> Mandy Chung said the following on 06/22/11 13:18:
>>  On 6/21/11 7:12 PM, Chris Hegarty wrote:
>>> [...]
>>>
>>> > I'm not sure the extra check in checkThreadState that the thread must
>>> > be RUNNABLE is valid. What if you are transitioning the thread from a
>>> > blocked to non-blocked state, you may still see it blocked on the
>>> > first call to getState.
>>>
>>> > L130-116: I agree with David that this test is not needed.
>>> > Like the RuntimeException listed in ProblemList.txt shows
>>> > that the target thread is in WAITING state but expected to
>>> > be RUNNABLE.
>>>
>>> The main thread executes goBlocked, goWaiting, goTimedWaiting, etc. 
>>> These methods set the state and then wait for the phaser to advance. 
>>> The phaser will not advance until MyThread triggers it, at which 
>>> point the thread should either be RUNNABLE or the expected state, 
>>> right? Or have I missed something?
>>>
>> With the change from calling arriveAndAwaitAdvance to calling arrive, 
>> I think you're probably right that the thread should either be 
>> RUNNABLE or the expected state.  If calling arriveAndAwaitAdvance, the 
>> thread delays and waits for the main thread to arrive.  The main 
>> thread may see that the target thread is in a state waiting for phaser 
>> to advance (depending on the implementation).
>>
>>> I added this extra check since we are now relaxing the check for the 
>>> expected state. I just thought it would be more correct than allowing 
>>> any state, but if you feel it too strict ( or still incorrect ) I can 
>>> remove it.
>>>
>>
>> With the change to call arrive, it seems fine to keep this check.  I'd 
>> like to get David's opinion on this.
>>
>>> > I also don't understand why you moved the terminated check to after
>>> > the join() - if the thread is failing to terminate then the join(),
>>> > which is  untimed, will simply not return and the test will hang
>>> > until timed-out  by the harness.
>>>
>>> > L98: Are you seeing some timing issue if you keep this
>>> > checkThreadState
>>> >     before the join and thus you moved it after the join?
>>>
>>> No timing issue. I did this for simplicity, given that the state 
>>> should be TERMINATED when join returns. Either way MyThread.run must 
>>> complete before the threads state will be set to TERMINATED. Invoking 
>>> checkThreadState before that point just seems more likely encounter 
>>> retries. I'm ok with either, just let me know if you want it reverted 
>>> back to the original.
>>>
>> The thread could move to TERMINATED state once it completes execution 
>> and while the main thread is not yet notified.  Since there is no 
>> timing issue and MyThread is calling arrive rather than 
>> arriveAndAwaitsAdvance, I would say keep the checkThreadState call 
>> before the join.
>>
>>> > I also don't think the use of the Phaser is appropriate here as you
>>> > are actually delaying the thread from making the state change. In the
>>> > original code the target thread signals the main thread that it is
>>> > about to go to state X and continues to advance to state X (modulo
>>> > preemption etc). But with the Phaser the target thread indicates it
>>> > is about to go to state X and then waits for the main thread -
>>> > consequently it is more likely that when the main thread calls
>>> > checkThreadState that the target has not yet reached the desired
>>> > state and so the main thread will have
>>> > to loop. This isn't incorrect it just seems to me that in the "wrong"
>>> > configuration the test may not take a lot longer in relative terms.
>>> > Maybe the additional clarity is worth it though ...
>>>
>>> When MyThread invokes arriveAndAwaitAdvance, then it should be the 
>>> final party to arrive and therefore "probably" shouldn't wait. But 
>>> you raise a good point, myThread should really just invoke 
>>> phaser.arrive() rather that arriveAndAwaitAdvance.
>>>
>>> Updated Webrev:
>>>   http://cr.openjdk.java.net/~chegar/7021010/jdk8.webrev.01/webrev/
>> Looks good.  Thanks for fixing this timing issue.
>> Mandy