RFR: JDK-8215550: Debugger does not work after reattach

[Chris Plummer]

Hi Gary,

When the "exit" or "quit" is done, aren't all threads resumed at that 
point, and shouldn't that result in the command loop being unblocked?

thanks,

Chris

On 1/29/19 8:09 AM, Gary Adams wrote:
> Significant protections are put in place to protect the commandLoop
> from multiple events that that have a suspend-all policy. The
> commandLoop uses a special block variable to ensure only
> a VirtualMachine or ThreadReference call to resume() will unblock
> the commandLoop. See
>
>   src/jdk.jdwp.agent/share/native/libjdwp/eventHelper.c
>
> In this particular bug report, the user was stopped at a breakpoint
> when they sent the "exit" command. The same effect can be produced
> with a "quit" command or any killing of the debugger process.
>
> When the second session is started the commandLoop is still blocked,
> so a new breakpoint will never be dequeued from the commandQueue.
>
> The proposed workaround will ensure the commandLoop is unblocked
> when a new session is started.
>
>   Issue: https://bugs.openjdk.java.net/browse/JDK-8215550
>   Webrev: http://cr.openjdk.java.net/~gadams/8215550/webrev.00/
>
> All testing has been done by manually replicating the reported
> command sequences. I'll see if an existing breakpoint test can be
> enhanced to cover this scenario.