[jira] [Created] (QPID-5637) qpid.messaging Issues With Forking

["Brian Bouterse (JIRA)" <ji...@apache.org>]

Brian Bouterse created QPID-5637:
------------------------------------

             Summary: qpid.messaging Issues With Forking
                 Key: QPID-5637
                 URL: https://issues.apache.org/jira/browse/QPID-5637
             Project: Qpid
          Issue Type: Bug
          Components: Python Client
    Affects Versions: 0.24
            Reporter: Brian Bouterse
             Fix For: 0.27, 0.26, 0.24, 0.22, 0.18


qpid.messaging has an issue with forking in the following situation.

1.  A parent Python process imports and uses qpid.messaging to connect to a a Qpid broker
2.  The parent process forks a child process
3.  The child process imports qpid.messaging and tries to connect to a Qpid broker.

I expected to see the child process use qpid.messaging normally as it would if it weren't forked in the way described above.  Instead, the server receives the opening of a TCP socket, but the client never sends the AMQP protocol announcement.

The root cause of this issue is in the file descriptors registered by the Selector object inside of qpid.messaging.  The Selector object uses a singleton pattern to provide a reference to the same Selector object no matter how many times you call it.  This selector object already has registered file descriptors with the filesystem, which allow the selector to read/write data in an I/O efficient manner.

When forking occurs, the child process receives a copy of the Python running space (ie: the Selector singleton), but the kernel is not registered with file descriptors that are available in the child process' new file descriptor table.  This breaks usage of qpid.messaging in the client process because when qpid.messaging relies on the epoll functionality of Selector, Selector does not fulfill that expectation.

The solution is to have the class method that implements the singleton pattern on the Selector object to be process aware, and implement the singleton pattern per process.



--
This message was sent by Atlassian JIRA
(v6.2#6252)

---------------------------------------------------------------------
To unsubscribe, e-mail: dev-unsubscribe@qpid.apache.org
For additional commands, e-mail: dev-help@qpid.apache.org