[jira] [Commented] (QPID-8206) [linearstore] Deadlock possible in InactivityFireEvent if fire() is called at the same time as cancel()

["Kim van der Riet (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/QPID-8206?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16504958#comment-16504958 ] 

Kim van der Riet commented on QPID-8206:
----------------------------------------

Pavel Moravec has found a reproducer:

0) {{rm -rf /var/lib/qpidd/.qpidd # just to start with absolutely clean table}}


1) set

{{journal-flush-timeout=50ms}}

to qpidd.conf - the lower the better. I reproduce the deadlock always within a minute or two with this value, but it took ~10 minutes with default 500ms (I think).


2) run this script that sporadically sends and receives a durable message to a queue that is time to time deleted - and it does so concurrently for 50 queues:
{noformat}
for i in $(seq 1 50); do
  while true; do
    echo "$(date): loop $i"
    qpid-send -a "DurableTest-${i}; {create:always, node:{type:queue, durable:true}}" -m 1 --content-size=1100 --durable=yes
    qpid-receive -a DurableTest-${i} --print-content=no 2> /dev/null
    sleep 0.2
  done &
done

for i in $(seq 1 50); do
  while true; do
    echo "$(date): deleting queue $i"
    qpid-config del queue DurableTest-${i} --force
    sleep $((RANDOM%5)).$((RANDOM%10))
  done &
done
{noformat}

3) check if qpidd responds, via e.g.:

{{while true; do date; qpid-stat -g; sleep 5; done}}

4) within a minute or so, deadlock comes to you and your broker.

> [linearstore] Deadlock possible in InactivityFireEvent if fire() is called at the same time as cancel()
> -------------------------------------------------------------------------------------------------------
>
>                 Key: QPID-8206
>                 URL: https://issues.apache.org/jira/browse/QPID-8206
>             Project: Qpid
>          Issue Type: Bug
>          Components: C++ Broker
>            Reporter: Kim van der Riet
>            Assignee: Kim van der Riet
>            Priority: Major
>
> A deadlock has been observed in InactivityFireEvent if {{InactivityFireEvent::fire()}} triggered by the timer occurs at almost the same time as {{InactivityFireEvent::cancel()}} on another thread, and which occurs if the queue is deleted.
> The mutex {{InactivityFireEvent::_ifeStateLock}} becomes deadlocked if the thread calling {{cancel()}} obtains the lock, but a fire event is imminent. The {{fire()}} call will then be blocked on this mutex. However, cancel cannot complete until fire competes owing to the sys::Time Monitor which waits for all fires to complete before allowing the cancel to occur.



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