Can PySerial's write method be called by multiple threads?

Joel Koltner zapwireDASHgroups at
Wed Aug 25 21:02:27 CEST 2010

"Thomas Jollans" <thomas at> wrote in message 
news:mailman.36.1282762569.29448.python-list at
> I expect that it gives away the GIL to call the resident write() function, 
> to
> allow other threads to run while it's sitting there, blocking. I haven't
> looked at the code, so maybe it doesn't hand over the GIL, but if it 
> doesn't,
> I'd consider that a bug rather than a feature: the GIL shouldn't be abused 
> as
> some kind of local mutex, and only gets in the way anyway.

Ah, I expect you're correct.  I'm still largely a Python newbie, and only know 
enough about things like the GIL to get myself into trouble.

> Speaking of the GIL, you shouldn't rely on it being there. Ever. It's a
> necessary evil, or it appears to be necessary. but nobody likes it and if
> somebody finds a good way to kick it out then that will happen.

OK, but presumably I can't know whether or not someone who wrote a library 
like pySerial relied on it or not.  Although I suppose this is really a 
documentation bug -- pySerial's documentation doesn't talk about 
multi-threaded access directly, although their "minicom" example does 
demonstrate it in action.

Thanks for the help,

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