[Twisted-Python] Logging observers and threads

exarkun at twistedmatrix.com exarkun at twistedmatrix.com
Thu Jul 12 09:47:03 EDT 2012

On 11:32 am, itamar at itamarst.org wrote:
>On 07/12/2012 05:17 AM, Tristan Seligmann wrote:
>>3) log observers should expect to be inovked in non-reactor threads,
>>making this a Mantissa bug.
>In theory this is the case - the logging howto says "The observer needs
>to be thread safe if you anticipate using threads in your program." The
>API docs don't mention threads, though..
>In practice however, probably every custom observer gets this wrong, so
>we really need some infrastructure to make this easier or to fix it.
>Possibly we should have some way to indicate an observer is thread- 
>assume by default they are not, and if they are not wrap them in a
>reactor.callFromThread wrapper.

The logging system is already a bottleneck in some applications.  Doing 
even more work to try to make it properly thread-safe will probably slow 
it down even more.

I think it was a mistake to try to make it possible to use 
twisted.python.log free-threaded.  I think we should think about getting 
rid of this claimed feature.  Perhaps it could be replaced with a more 
explicit, probably more restricted, logging feature for non-reactor 

Unless someone can magically fix the threading issues without hurting 
performance.  Then, great, go for it.
>I would also like some infrastructure to make the file log observer run
>in its own thread, but that's almost the opposite use case :)

Sure, but that's probably based on top of an asynchronous file I/O API 
that's not explicitly thread-based (but probably is thread-based in 
practice, because what other kind of asynchronous file I/O even exists).

Also, to explicitly answer Tristan's question:

    It's a bug in the Mantissa log observer.


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