Hi Robbin,
Looks good.
Thanks,
/Erik
On 2018-10-26 16:33, Robbin Ehn wrote:
Hi, please review.
When the VM thread executes a handshake it uses different ThreadsLists
during
the execution. A JavaThread that is armed for the handshake when it is
already
in the exit path in VM will cancel the handshake. Even if the VM
thread cannot
see this thread after the initial ThreadsList which where used for
arming, the
handshake can progress when the exiting thread cancels the handshake.
But if a third thread takes a ThreadsList where the exiting JavaThread
is present and tries to execute a VM operation, hence waiting on VM
thread to finish the handshake, the JavaThread in the exit path can
never reach the handshake cancellation point. VM thread cannot
finishes the handshake and the third thread is stuck waiting on the VM
thread.
To allow holding a ThreadsList when executing a VM operation we
instead let the
VM thread use the same ThreadsList over the entire handshake making
all armed
threads visible to the VM thread at all time. And if VM thread spots a
terminated thread it will count that thread is already done by only
clearing
it's operation.
Passes local stress testing, t1-5 and the deadlock is no longer
reproduce-able.
Added a jtreg handshake + thread suspend test as a reproducer.
Issue: https://bugs.openjdk.java.net/browse/JDK-8212933
Code: http://cr.openjdk.java.net/~rehn/8212933/v1/webrev/
Thanks, Robbin
