On 15/09/2017 8:17 PM, Alan Bateman wrote:
On 15/09/2017 02:47, David Holmes wrote:
Hi Adam,
I am still very much torn over this one. I think the idea of
print-and-exit flags for a potentially hosted library like the JVM is
just wrong - we should never have done that, but we did. Fixing that
by moving the flags to the launcher is far from trivial**. Endorsing
and encouraging these sorts of flag by adding JNI support seems to be
sending the wrong message.
** I can envisage a "help xxx" Dcmd that can read back the info from
the VM. The launcher can send the Dcmd, print the output and exit. The
launcher would not need to know what the xxx values mean, but would
have to intercept the existing ones.
Another option is just to be aware of these flags (are there more than
jdwp and Xlog?) and deal with them specially in your custom launcher -
either filter them out and ignore them, or else launch the VM in its
own process to respond to them.
Any changes to the JNI specification need to go through the CSR process.
Yes, it would require an update to the JNI spec, also a change to the
JVM TI spec where Agent_OnLoad returning a non-0 value is specified to
terminates the VM. The name and value needs discussion too, esp. as the
JNI spec uses negative values for failure.
In any case, I'm also torn over this one as it's a corner case that is
only interesting for custom launchers that load agents with options that
print usage messages. It wouldn't be hard to have the Agent_OnLoad
specify a printf hook that the agent could use for output although there
are complications with agents such as JDWP that also announce their
transport end point. Beyond that there is still the issue of the custom
launcher that would need to know to destroy the VM without reporting an
error.
So what happened to the more meaty part to this which is fixing the
various cases in HotSpot that terminate the process during
initialization? I would expect some progress could be made on those
cases while trying to decide whether to rev the JNI and JVM TI specs to
cover the help case.
Trying to eliminate the vm_exit_during_initialization paths in hotspot
is a huge undertaking IMHO.
David
-Alan
