[
https://issues.apache.org/jira/browse/QPID-5637?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Brian Bouterse updated QPID-5637:
---------------------------------
Description:
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.
[Forking bring child descriptors with
it|http://man7.org/linux/man-pages/man2/fork.2.html]. I expected the file
descriptors on the parent and the child to be the same, and to reference the
same socket, so I expect qpid.messaging to work without any modification.
Surprisingly, it does not.
There is at least one place where I do understand how this can be avoided. One
of the issues is that the file descriptors registered by the Selector object
inside of qpid.messaging are stale after the fork. 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. See the attached [pid_aware_selector.patch] for an
example of this.
The [pid_aware_selector.patch] does allow communication to flow, but queue
creation and deletion sometimes fail in strange ways. For instance, in the
child process, code that creates a queue, reads information about that queue
next. The queue was created, yet the read says that the queue can't be found.
Very strange. You can see those things fail using the following simple example:
1. clone our fork of kombu: `git clone g...@github.com:pulp/kombu.git`
2. Change into the kombu folder `cd kombu`
3. Switch to the branch containing the qpid code: `git checkout
pulp-dep-3.0.15-with-qpid`
4. Install kombu onto your system or virtualenv (I do it systemwide using
sudo): `sudo python setup.py develop`
5. install celery version 3.1.11. I do it using pip. `sudo pip install
celery==3.1.11`
6. Install qpid.messaging and qpidtoollibs. One way I do it is systemwide
using pip. `sudo pip install qpid-tools qpid-python`
7. Start up qpidd (We've been testing with 0.24 and auth off). `sudo -u
qpidd qpidd --auth=no`
8. Put the attached file tasks.py into a directory
9. Open two terminals and change their working directory to be the same as
step 8.
10. In one one terminal start the celery worker `celery worker -A tasks
--loglevel=INFO -c1`
11. In the other terminal dispatch 10 tasks `python tasks.py`
You should see exceptions raised similar to those in the attached file
[celery_worker_output.txt]
Note, that the code on the pulp-dep-3.0.15-with-qpid branch of kombu monkey
patches qpid.messaging with the selector patch referenced above, and also one
or two other bugfix patches. You can see that [monkey patching done
here|https://github.com/pulp/kombu/blob/pulp-dep-3.0.15-with-qpid/kombu/transport/qpid.py#L45].
This should have no implications on this issue, but I want to be explicit
about it.
A potential fix: Celery supports a callback after child processes are forked,
allowing the call to cleanup/reset exactly these types of things. I could wire
up that callback if such a thing existed on qpid.messaging. For testing
purposes, you could put code you want to do this cleanup in the task code
before the call to
was:
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.
[Forking bring child descriptors with
it|http://man7.org/linux/man-pages/man2/fork.2.html]. I expected the file
descriptors on the parent and the child to be the same, and to reference the
same socket, so I expect qpid.messaging to work without any modification.
Surprisingly, it does not.
There is at least one place where I do understand how this can be avoided. One
of the issues is that the file descriptors registered by the Selector object
inside of qpid.messaging are stale after the fork. 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. See the attached [pid_aware_selector.patch] for an
example of this.
The [pid_aware_selector.patch] does allow communication to flow, but queue
creation, and deletion seem to fail. You can see those things fail using the
following simple example:
1. clone our fork of kombu: `git clone g...@github.com:pulp/kombu.git`
2. Change into the kombu folder `cd kombu`
3. Switch to the branch containing the qpid code: `git checkout
pulp-dep-3.0.15-with-qpid`
4. Install kombu onto your system or virtualenv (I do it systemwide using
sudo): `sudo python setup.py develop`
5. install celery version 3.1.11. I do it using pip. `sudo pip install
celery==3.1.11`
6. Install qpid.messaging and qpidtoollibs. One way I do it is systemwide
using pip. `sudo pip install qpid-tools qpid-python`
7. Start up qpidd (We've been testing with 0.24 and auth off). `sudo -u
qpidd qpidd --auth=no`
8. Put the attached file tasks.py into a directory
9. Open two terminals and change their working directory to be the same as
step 8.
10. In one one terminal start the celery worker `celery worker -A tasks
--loglevel=INFO -c1`
11. In the other terminal dispatch 10 tasks `python tasks.py`
You should see exceptions raised similar to those in the attached file
[celery_worker_output.txt]
Note, that the code on the pulp-dep-3.0.15-with-qpid branch of kombu monkey
patches qpid.messaging with the selector patch referenced above, and also one
or two other bugfix patches. You can see that [monkey patching done
here|https://github.com/pulp/kombu/blob/pulp-dep-3.0.15-with-qpid/kombu/transport/qpid.py#L45].
This should have no implications on this issue, but I want to be explicit
about it.
> 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: 0.18, 0.22, 0.24, 0.26, 0.27
>
> Attachments: celery_worker_output.txt, pid_aware_selector.patch,
> tasks.py
>
>
> 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.
> [Forking bring child descriptors with
> it|http://man7.org/linux/man-pages/man2/fork.2.html]. I expected the file
> descriptors on the parent and the child to be the same, and to reference the
> same socket, so I expect qpid.messaging to work without any modification.
> Surprisingly, it does not.
> There is at least one place where I do understand how this can be avoided.
> One of the issues is that the file descriptors registered by the Selector
> object inside of qpid.messaging are stale after the fork. 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. See the attached
> [pid_aware_selector.patch] for an example of this.
> The [pid_aware_selector.patch] does allow communication to flow, but queue
> creation and deletion sometimes fail in strange ways. For instance, in the
> child process, code that creates a queue, reads information about that queue
> next. The queue was created, yet the read says that the queue can't be
> found. Very strange. You can see those things fail using the following
> simple example:
> 1. clone our fork of kombu: `git clone g...@github.com:pulp/kombu.git`
> 2. Change into the kombu folder `cd kombu`
> 3. Switch to the branch containing the qpid code: `git checkout
> pulp-dep-3.0.15-with-qpid`
> 4. Install kombu onto your system or virtualenv (I do it systemwide using
> sudo): `sudo python setup.py develop`
> 5. install celery version 3.1.11. I do it using pip. `sudo pip install
> celery==3.1.11`
> 6. Install qpid.messaging and qpidtoollibs. One way I do it is systemwide
> using pip. `sudo pip install qpid-tools qpid-python`
> 7. Start up qpidd (We've been testing with 0.24 and auth off). `sudo -u
> qpidd qpidd --auth=no`
> 8. Put the attached file tasks.py into a directory
> 9. Open two terminals and change their working directory to be the same as
> step 8.
> 10. In one one terminal start the celery worker `celery worker -A
> tasks --loglevel=INFO -c1`
> 11. In the other terminal dispatch 10 tasks `python tasks.py`
> You should see exceptions raised similar to those in the attached file
> [celery_worker_output.txt]
> Note, that the code on the pulp-dep-3.0.15-with-qpid branch of kombu monkey
> patches qpid.messaging with the selector patch referenced above, and also one
> or two other bugfix patches. You can see that [monkey patching done
> here|https://github.com/pulp/kombu/blob/pulp-dep-3.0.15-with-qpid/kombu/transport/qpid.py#L45].
> This should have no implications on this issue, but I want to be explicit
> about it.
> A potential fix: Celery supports a callback after child processes are
> forked, allowing the call to cleanup/reset exactly these types of things. I
> could wire up that callback if such a thing existed on qpid.messaging. For
> testing purposes, you could put code you want to do this cleanup in the task
> code before the call to
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