Is print thread safe?

[Cameron Simpson]

On 12Aug2014 08:01, Marko Rauhamaa <marko at pacujo.net> wrote:
>Steven D'Aprano <steve+comp.lang.python at pearwood.info>:
>> Personally, I believe that print ought to do its own locking. And
>> print is a statement, although in this case there's no need to support
>> anything older than 2.6, so something like this ought to work:
>>
>> from __future__ import print_function
>>
>> _print = print
>> _rlock = threading.RLock()
>> def print(*args, **kwargs):
>>     with _rlock:
>>         _print(*args, **kwargs)
>
>Could this cause a deadlock if print were used in signal handlers?

At the C level one tries to do as little as possible in q signal handler.  
Typically setting a flag or putting something on a queue for later work.

In Python that may be a much smaller issue, since I imagine the handler runs in 
the ordinary course of interpretation, outside the C-level handler context.

I personally wouldn't care if this might deadlock in a handler (lots of things 
might; avoid as many things as possible). Also, the code above uses an RLock; 
less prone to deadlock than a plain mutex Lock.

Cheers,
Cameron Simpson <cs at zip.com.au>

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