RFR: 8368625: com/sun/net/httpserver/ServerStopTerminationTest.java fails intermittently in tier7

[Daniel Fuchs]

On Tue, 7 Oct 2025 15:50:30 GMT, Mark Sheppard <msheppar at openjdk.org> wrote:

>> I believe that increasing the timeout might help, as it seems to be happening due to the machine load. I'm going to make a pr increasing the timeout to 20 from 5 (similar to what it was when timeout factor was 4).
>
> The extending of the stop duration may not have the desired effect of eliminating what appears to be a race condition in the test
> 
> One of the recorded failures is  for the temporal condition
> 
>         // The shutdown should take at least as long as the exchange duration
>         if (elapsed < exchangeDuration.toNanos()) {
>             fail("HttpServer.stop terminated before exchange completed");
>         }
> 
> This is a somewhat dubious constraint and can’t always be met
> 
> The test assumes that the participating threads are all actively executing simultaneously, which may not be true
> They may be scheduled to run rather than actually running.
> 
> Restating the objective of the test
> Objective: to ensure that the stop request is not processed while there are extant exchanges 
> 
> Potential race scenario:
> 
> Server started creates exchange which waits for a signal to complete
> 
> Exchange completion thread starts waits for 1 seconds before it can signal exchange to compete — the complete signal will be thus invoked sometime after 1 second depending on OS thread scheduling
> 
> Main thread continues and invokes a stop which has a max wait time of 5 seconds  for extant exchanges to complete — so max completion time of stop is 5 seconds ++ i.e. could be slightly longer than 5 seconds again subject to OS scheduling
> 
> Temporal condition imposed by test
> 
>         // The shutdown should take at least as long as the exchange duration
>         if (elapsed < exchangeDuration.toNanos()) {
>             fail("HttpServer.stop terminated before exchange completed");
>         }
> 
>         // The delay should not have expired
>         if (elapsed >= delayDuration.toNanos()) { 
>             fail("HttpServer.stop terminated after delay expired");
>         }
> 
> 1. States elapsed time of stop should be less than the duration of the exchange exchangeDuration. BUT exchangeDuration is not the
> duration of the exchange completion. Rather, it is the time delay before the exchange thread is signalled to complete. 
> The actual completion of the exchange may be sometime later, again depending on OS thread scheduling.
> 
> Second condition is that the elapsed time of the stop should be less than or equal to the stop delay. BUT if the full timeout for the 
> stop expires as per
> 
> server.stop will wait a max of N (5) seconds before terminating as per
> 
>         try {
>             // waiting for the duration of the delay, unless released before
>             finishedLatch.await(delay, TimeUnit.SECONDS);
> 
>         } catch (InterruptedExceptio...

I believe Mark is right - there is an issue with the timing logic in this method. The virtual thread that sleeps before calling complete.countDown() may finish sleeping and call countDown() before server.stop() is called. Good analysis @msheppar !

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PR Comment: https://git.openjdk.org/jdk/pull/27670#issuecomment-3381344845