crash with exception in libuv's threadpool.c on OS X Mavericks 10.9.5 about node-xpc-connection HOT 10 CLOSED

I took a quick look and I think I know what's happening:

• XPC will report events to the handler which was registered here: https://github.com/sandeepmistry/node-xpc-connection/blob/master/src/XpcConnection.cpp#L52
• And it will do so in the dispatch queue which was setup here: https://github.com/sandeepmistry/node-xpc-connection/blob/master/src/XpcConnection.cpp#L49
• That means that handleEvent runs in a thread other than the loop thread: https://github.com/sandeepmistry/node-xpc-connection/blob/master/src/XpcConnection.cpp#L64
• handleEvent calls uv_queue_work, which is not thread-safe, so things will eventually blow up

Here is a suggestion:

• Use a thread-safe queue (an array with a lock will do) and store the events there from handleEvent
• Use an uv_async_t handle to process the queue in the loop thread: uv_async_send is thread safe: http://docs.libuv.org/en/latest/async.html#c.uv_async_send
• Profit?

Hope that helps!

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@vielmetti this might also be useful for getting a stack trace: https://github.com/ddopson/node-segfault-handler

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Thanks @saghul that is tremendously helpful.

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@saghul thanks for the explanation and suggestion!

Would you mind quickly reviewing 2f7734b before I merge into master?

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Looks good!
On Mar 31, 2015 2:52 AM, "Sandeep Mistry" [email protected] wrote:

@saghul https://github.com/saghul thanks for the explanation and
suggestion!

Would you mind quickly reviewing 2f7734b
2f7734b
before I merge into master?

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Thanks! I'm putting together a test environment with this code, the new noble release, and support for the new Sensortag 2 - hope to exercise this soon in the same way that I did before.

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I just had another look. I initially thought about having a mutex + queue + async handle per XPC connection. Alternatively, you can also have a global async handle, which you initialize only once with uv_once: http://docs.libuv.org/en/v1.x/threading.html?highlight=uv_once#once-only-initialization

Not sure about the performance impact of either, but both should work.

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@saghul good suggestion, I've made changes to have one mutex + queue + async per XPC connection: 4be4f4a

Would you mind quickly reviewing again?

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@vielmetti I've published a new version (0.1.3) to npm, with the changes @saghul suggested.

@saghul thanks again for your help!

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Glad to help!
On Apr 5, 2015 15:27, "Sandeep Mistry" [email protected] wrote:

@vielmetti https://github.com/vielmetti I've published a new version
(0.1.3) to npm, with the changes @saghul https://github.com/saghul
suggested.

@saghul https://github.com/saghul thanks again for your help!

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