RFR: 8072701: resume001 failed due to ERROR: timeout for waiting for a BreakpintEvent [v3]

[Chris Plummer]

On Fri, 12 Jul 2024 02:44:28 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Chris Plummer has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix copyright and jcheck error
>
> test/hotspot/jtreg/vmTestbase/nsk/jdi/ThreadReference/resume/resume001.java line 382:
> 
>> 380:             if (expresult != returnCode0) {
>> 381:                 vm.resume();
>> 382:                 vm.resume();  // for case error when both VirtualMachine and the thread2 were suspended
> 
> Pre-existing but I don't understand the comment. Why would you need 2 `vm.resume()` here? If `thread2` was suspended directly don't you need a `thread2.resume()`?

First just to clarify a general JDI feature about thread suspending and resuming. You can undo a ThreadReference.suspend() or a thread suspended as the result of an event by dong a vm.resume(). This is documented in the JDI API spec, which talks about suspendCounts and how various APIs and event delivery affect them.

I was  tempted to clean up these vm.resume() calls but opted not to. The point being made in the comment is that worse case thread2 was suspended by a breakpoint or thread2.suspend() and all threads were suspended by a vm.resume() (meaning thread2 could have a suspendCount of 2). Two vm.resumes() take are done to make sure thread2 gets resumed under this situation. However, one of the vm.resume calls could instead be a thread2.resume(). Doing two vm.resume() calls was probably just laziness by the original  authors. It works though.

However, by my accounting at any failure point thread2 never has a suspendCount > 1, so really just one vm.resume() would be enough.

The original code did these two vm.resume() calls unconditionally, but they are not needed if there was no error.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20088#discussion_r1675243246