[erlang-questions] Is ei_xreceive_msg() thread safe?

Peter Membrey peter@REDACTED
Tue Aug 27 09:30:47 CEST 2013

Hi guys,

I've got a fairly basic C Node set up where I have the main thread running in a loop with ei_xreceive_msg() and a number of "callback" threads that execute functions and write data using ei_send() to the shared socket (connecting to the Erlang node).

Originally I had a lot of data corruption (the Erlang node crashing due to corrupt data) because of incorrect locking on socket writes. I added mutexes to the ei_send() calls and this problem seemed to go away.

However I've had a couple of occasions where the system has been quiet and then suddenly become busy where corrupt data has still been sent to the Erlang node. I'm positive all the places where I do ei_send() are protected, but that got me wondering about ei_xreceive_msg().

>From what I can find, ei_xreceive_msg() automatically handles heartbeats for you and I guess that means it will send some sort of reply on that socket. If the heart beat is being sent at the same time as some other process tries to write to the socket, is it possible that the two could get interleaved or something? I would honestly have thought it unlikely but I'm running out of ideas.

Assuming it's possible, how could I add a mutex in this case? The call itself blocks, so I can't wrap the whole call in the mutex else nothing else will be able to send data, and there's no way to pass a mutex into the call itself. So as far as I can tell, there's no way to protect these writes and prevent them from getting mixed up with other writes on that socket.

Does anyone have any ideas? I'm quite willing to accept I could be doing something pretty stupid, but I'm really out of ideas as to what that might be...

Thanks in advance!

Kind Regards,

Peter Membrey

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