Race condition of message handler in connection recovery in Hedwig client
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Key: BOOKKEEPER-56
URL: https://issues.apache.org/jira/browse/BOOKKEEPER-56
Project: Bookkeeper
Issue Type: Bug
Components: hedwig-client
Affects Versions: 3.4.0
Reporter: Gavin Li
Fix For: 3.4.0
There's a race condition in the connection recovery logic in Hedwig client. The
message handler user set might be overwritten incorrectly.
When handling channelDisconnected event, we try to reconnect to Hedwig server.
After the connection is created and subscribed, we'll call StartDelivery() to
recover the message handler to the original one of the disconnected connection.
But if during this process, user calls StartDelivery() to set a new message
handler, it will get overwritten to the original one.
The process can be demonstrated as below:
main thread netty worker thread
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StartDelivery(messageHandlerA)
(connection Broken here, and recovered later...)
ResponseHandler::channelDisconnected() (connection disconnected event
received)
new
SubscribeReconnectCallback(subHandler.getMessageHandler()) (store
messageHandlerA in SubscribeReconnectCallback to recover later)
client.doConnect() (try reconnect)
doSubUnsub() (resubscribe)
SubscriberResponseHandler::handleSubscribeResponse() (subscription succeeds)
StartDelivery(messageHandlderB)
SubscribeReconnectCallback::operationFinished()
StartDelvery(messageHandlerA)
(messageHandler get overwritten)
I can stably reproduce this by simulating this race condition by put some sleep
in ResponseHandler.
I think essentially speaking we should not store messageHandler in
ResponseHandler, since the message handler is supposed to be bound to
connection. Instead, no matter which connection is in use, we should use the
same messageHandler, the one user set last time. So I think we should change to
store messageHandler in the HedwigSubscriber, in this way we don't need to
recover the handler in connection recovery and thus won't face this race
condition.
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