[Python-Dev] pthread sem PyThread_acquire_lock (original) (raw)

Phillip Sitbon phillip.sitbon+python-dev at gmail.com
Mon Jun 29 21:33:00 CEST 2009

I'll do my best to try and explain/contribute, but please feel free to correct anything I get wrong.

I believe the "swallowing" he's referring to is the ignoring of errno EINTR. I don't think that's the correct place to handle signals to begin with- why not just use the signal module to deal with such a scenario?

http://docs.python.org/dev/library/signal.html#module-signal

AFAIK, ignoring EINTR doesn't preclude the calling of signal handlers. There are many functions that don't return this value anymore, making them reentrant. I remember a number of years ago when it wasn't part of any standard to return EINTR or not, and so the only way to provide consistent behavior was to ignore it and loop. I'm not sure if that is still the case.

A great example is reading from a socket. Whether or not it can be interrupted depends on the platform, so catching Ctrl+C often requires a timeout loop.

Also, remember that signals are asynchronous in the sense that they are handled outside the normal execution flow of a program. Checking for EINTR probably isn't the best way to determine if a signal has been sent to the program.

Cheers,

Phillip

On Sat, Jun 27, 2009 at 3:58 PM, Florian Mayer <flormayer at aim.com> wrote:

Martin v. Löwis wrote:

Can you please explain what you mean by "swallowing"? The signals don't get through when acquiring the lock. What is the sequence of actions triggering the case you are talking about, what happens, and what do you expect to happen instead? Easiest way is to create a Queue.Queue and call .get() on it and try to Ctrl-C it. Also, how would you fix this (in principle, not what the specific patch would look like)? Remove the loop that explicitly does this in a new function and use that one in threadmodule.c for lock.acquire. Regards, Martin Best regards, Florian PS: Excuse me, I messed up things once again.

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