Experimental Physics and
Industrial Control System

<[email protected]> · Tue, 30 Sep 2014 13:31:41 +0000

From: Kasemir, Kay [mailto:[email protected]]
> For SNS beam line updates we started using cothread, but now prefer
> https://pypi.python.org/pypi/CaChannel
> 
> cothread has a very nice API, but it uses its own type of cooperative
> threads which prohibit use of plain python threads.

THIS IS NOT TRUE.

Cothreads and plain threads interact in a particular way which requires careful understanding.  In particular, the cothread API can only be used from one thread -- it is not possible to perform a cothread blocking operation in another thread, and it's not safe (at present) to perform a cothread wakeup from another thread.

The current cothread way is to do all the cothread work in a thread dedicated to cothread and to use the mechanisms provided by cothread for communicating with other threads.

Michael Davidsaver and I have briefly discussed providing deeper support in cothread for multiple threads, but so far it's not been very clear to me what the requirements are.  

> We need to use both a CA client and a CA server
> (http://code.google.com/p/pcaspy/) within the same python program, and
> would like to have the option of using additional python libraries
> which in turn might create their own threads. So far, we found no
> issues when combining pcaspy and CaChannel within the same python
> program.

What issues have you encountered when using cothread in this context?  If you wish to call into cothread from another thread I suggest in the first instance using the Callback() mechanism.

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System