Hello,
Please review the following fix for JDK12:
http://cr.openjdk.java.net/~cjplummer/8199811/webrev.00
https://bugs.openjdk.java.net/browse/JDK-8199811
The root of the problem is that there is no code in the solaris or
windows AttachListener support that ensures that the listener is done
being initialized before attaching and attempting to enqueue the first
command. The enqueue operation fails when is sees that the listener is
not attached yet.
I was able to force this failure to happen every time by adding a 10
second sleep in attach_listener_thread_entry() just before the call to
AttachListener::set_initialized(). This did not cause macosx or linux to
fail, but did make solaris fail (failures had not been noted previously)
and windows to fail (failures previously had been observed, but very
rarely).
The proposed fix is to have the enqueue code sleep for up to 20 seconds
(in 1 second intervals) waiting for initialization to be complete. I
found this fixed the problem, even with the 10 second sleep in
attach_listener_thread_entry() still in place. A shorter sleep is
probably fine. I'm open to suggestions. Since this timing issue was so
rare, my guess is that a single 1 second sleep is likely to always fix
it, but since it is so hard to reproduce (without the 10 second sleep in
place), I can't say for sure.
Another approach to fixing this would be to use some sort of
synchronization between the init and enqueue code, like a condition
variable. I think I know how to do this with pthread_cond_wait() and
pthread_cond_signal(), although it gets to be a bit tricky since I'd
probably have to make the enqueue code create the condvar if
initialization is not yet complete, and then have the initialization
code check for the existence of the condvar when initialization is
complete, and signal on it if it exists. I'm pretty sure there's a
potential for race condition in there. I haven't thought it through
enough to say for sure. I also looked a bit at condition variable
support on windows, and it looks like I could do something similar there
too. However, I think the sleep approach I have implement is far more
straight forward and less error prone, so I'd prefer to stick with it if
others approve.
thanks,
Chris
