On Sat, 18 Mar 2023 00:22:54 GMT, Chris Plummer <cjplum...@openjdk.org> wrote:
>> The debuggee main method creates two threads and then starts them:
>>
>>
>> public static void main(String[] args) {
>> System.out.println("Howdy!");
>> Thread t1 = TestScaffold.newThread(new InvokeHangTarg(), name1);
>> Thread t2 = TestScaffold.newThread(new InvokeHangTarg(), name2);
>>
>> t1.start();
>> t2.start();
>> }
>>
>>
>> These threads will hit breakpoints which the debugger handles and issues an
>> invoke on the breakpoint thread. The threads run until they generate 100
>> breakpoints. There is an issue when these two threads are virtual threads.
>> Virtual threads are daemon threads. That means the JVM can exit while they
>> are still running. The above main() method is not waiting for these two
>> threads to exit, so main() exits immediately and the JVM starts the shutdown
>> process. It first must wait for all non-daemon threads to exit, but there
>> are none, so the JVM exits right away before the two threads are completed.
>> The end result of this early exit is that sometimes the invoke done by the
>> debugger never completes because the JVM has already issued a VMDeath event
>> and the debuggee has been disconnected.
>>
>> When these two threads are platform threads, the JVM has to wait until they
>> complete before it exits, so they will always complete. The fix for virtual
>> threads is to do a join with t1 and t2. This forces the main() method to
>> block until they have completed.
>
> Chris Plummer has updated the pull request incrementally with three
> additional commits since the last revision:
>
> - fix spelling error
> - add comment
> - minor formatting fix
Thumbs up. Thanks for adding the comment.
One possible nit typo...
test/jdk/com/sun/jdi/InvokeHangTest.java line 65:
> 63: try {
> 64: // The join ensures that the test completes before we exit
> main(). If we are using
> 65: // virtual threads, they are always daemon threads, and
> therefor the JVM will exit
nit typo: s/therefor/therefore/
-------------
Marked as reviewed by dcubed (Reviewer).
PR: https://git.openjdk.org/jdk/pull/13068
