RFR: 8289765: JDI EventSet/resume/resume008 failed with "ERROR: suspendCounts don't match for : VirtualThread-unparker"

[Kevin Walls]

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On Fri, 3 Mar 2023 18:16:25 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> The test failure is caused by the arrival of unexpected ThreadStartEvents, which mess up the debugger side. The events are for threads we normally only see getting created when using virtual threads, such as carrier threads and the VirtualThread-unparker thread. Theoretically this issue could happen without virtual threads due to other VM threads starting up such as Common-Cleaner, but we haven't seen it fail for that reason yet.
> 
> The test is testing proper thread suspension for ThreadStartEvent using each of the 3 suspension policy types. The debuggee creates a sequence of 3 debuggee threads, each one's timing coordinated with some complicated synchronization with the debugger using breakpoints and the setting of fields in the debuggee (and careful placement of suspend/resume in the debugger). The ThreadStartRequests that the debugger sets up always use a "count filter" of 1, which means the requests are good for delivering exactly 1 ThreadStartEvent, and any that come after the first will get filtered out. So when an an unexpected ThreadStartEvent arrives for something like a carrier thread, this prematurely moves the debugger on to the next step, and the synchronization with the debuggee gets messed up.
> 
> The first step in fixing this test was to remove the count filter, so the request can handle any number of ThreadStartEvents.
> 
> The next step was then fixing the test library code in EventHandler.java so it would filter out any undesired ThreadStartEvents, so the test just ends up getting one event, and always for the thread it is expecting. There are a few parts to this. One is improving EventFilters.filter() to filter out more threads that tend to be created during VM startup, including carrier threads and the VirtualThread-unparker thread.
> 
> It was necessary to add some calls EventFilters.filter() from EventHandler. This was done by adding a ThreadStartEvent listener for the "spurious" thread starts (those the test debuggee does not create). This listener is added by waitForRequestedEventCommon(), which is indirectly called by the test when is calls waitForRequestedEventSet().
> 
> There is a also 2nd place where the ThreadStartEvent listener for "spurious" threads is needed. It is now also installed with the default listeners that are always in place. It is needed when the test is not actually waiting for a ThreadStartEvent, but is waiting for a BreakpointEvent. waitForRequestedEventCommon() is not used in this case (so none of its listeners are installed), but the default listeners are always in place and can be used to filter these ThreadStartEvents. Note this filter will also be in place when calling waitForRequestedEventCommon(), but we can't realy on it when waitForRequestedEventCommon() is used for ThreadStartEvents because the spurious ThreadStartEvent will be seen and returned before we ever get to the default filter. So we actually end up with this ThreadStartEvent listener installed twice during  waitForRequestedEventCommon().
> 
> I did a bit of cleanup on the test, mostly renaming of threads and ThreadStartRequests so they are easier to match up with the iteration # we use in both the debuggee and debugger (0, 1, and 2). The only real change in the test itself is removing the filter count, and verifying that the ThreadStartEvent is for the expected thread.

test/hotspot/jtreg/vmTestbase/nsk/jdi/EventSet/resume/resume008.java line 150:

> 148:                     return;
> 149:                 }
> 150:             }

Not your typo here, but just below on line 157 now there's the "propety" spelling error which was in the failure logs.

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PR: https://git.openjdk.org/jdk/pull/12861