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From Gordon Sim <g...@redhat.com>
Subject Re: qpid-0.20 Execution exception: resource-locked
Date Mon, 05 Dec 2016 20:26:26 GMT
On 05/12/16 19:41, Bee wrote:
> Hello, I'm quite new here.  Hopefully, I can get some help for qpid-0.20 I'm using at
> A few times now, I get this error:
> [Protocol] error Execution exception: resource-locked: Cannot grant exclusive access
to queue   (qpid/broker/SessionAdapter.cpp:324)
> Please correct me, but my understanding is this is a race condition where connection
unexpectedly close, broker-client tries to re-initiate the session, but the exclusive queue
has not been freed yet.
> When this happens, client or broker (I'm not sure) stops trying to establish the session

It will happen when the broker thinks there is already a session using 
that queue. One possibility is that the client timed out due not not 
receiving a heartbeat before the broker did.

Because the client gets an explicit error, it does not try to reconnect 
(it only does that if the connection is lost).

> My question is, how can I ensure the session can re-establish again by itself.  And,
how can I reproduce this issue.

You could try sending the SIGSTOP signal to the broker. That prevents 
the broker sending out heartbeats, then send SIGCONT after 2*heartbeat 
interval so that the broker wakes up in time to process the reconnect, 
but may not have processed the disconnect fully. You'll need to run it 
several times and perhaps vary the time between stop and cont a little 
to try and reproduce.

> I've tried iptables, it seems to reconnect as it's supposed to.  I've tried qpid-config
del queue, I get msg that queue is deleted, but not the same error msg.
> I'm using these options for broker
> reconnect: true
> heartbeat: 1
> tcp_nodelay: true
> reconnect_timeout: 2.0

Just in passing, the reconnect_timeout is the maximum total time that 
the client will spend trying to reconnect. 2 seconds seems like a small 
value for that.

> reconnect_interval_min: 0.1
> reconnect_interval_max: 2.0
> Any insights will be very appreciated.

Steve's suggestion is probably the simplest, i.e. wait a bit longer 
before the first reconnect attempt to try and avoid the race.

In recent versions of the API, there is an explicit reconnect() method 
(assuming you are using c++ qpid::messaging of course) on Connection 
that you could use when catching this particular error. Not available on 
0.20 though, so would need a newer client.

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