RFR: 8212933: Thread-SMR: requesting a VM operation whilst holding a ThreadsListHandle can cause deadlocks
erik.osterlund at oracle.com
Fri Oct 26 14:37:34 UTC 2018
On 2018-10-26 16:33, Robbin Ehn wrote:
> Hi, please review.
> When the VM thread executes a handshake it uses different ThreadsLists
> the execution. A JavaThread that is armed for the handshake when it is
> 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
> 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
> it's operation.
> Passes local stress testing, t1-5 and the deadlock is no longer
> 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
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