RFR(XXS): 8227117: normal interpreter table is not restored after single stepping with TLH

Daniel D. Daugherty daniel.daugherty at oracle.com
Thu Jul 4 02:04:59 UTC 2019


Robbin recently discovered this issue with Thread Local Handshakes. Since
he's not available at the moment, I'm handling the issue:

     JDK-8227117 normal interpreter table is not restored after single 
stepping with TLH

When using Thread Local Handshakes, the normal interpreter table is
not restored after single stepping. This issue is caused by the
VM_ChangeSingleStep VM-op relying on SafepointSynchronize::end() to
restore the normal interpreter table for the "off" case.

Prior to Thread Local Handshakes, this was a valid assumption to make.
SafepointSynchronize::end() has been refactored into
disarm_safepoint() and it only calls Interpreter::ignore_safepoints()
on the global safepoint branch. That matches up with the call to
Interpreter::notice_safepoints() that is also on the global safepoint

The solution is for the VM_ChangeSingleStep VM-op for the "off" case
to call Interpreter::ignore_safepoints() directly.

Here's the webrev URL:


The fix is just a small addition to VM_ChangeSingleStep::doit():

    if (_on) {
+  } else {
+    Interpreter::ignore_safepoints();

Everything else is just new logging support for future debugging of
interpreter table management and single stepping.

Tested this fix with Mach5 Tier[1-3] on the standard Oracle platforms.
Mach5 Tier[4-6] on standard Oracle platforms is running now.

Thanks, in advance, for questions, comments or suggestions.


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