[Python-ideas] WSAPoll and tulip (original) (raw)

Guido van Rossum guido at python.org
Tue Nov 27 17:06:02 CET 2012

I wasn't there, and it's been 7 years since I last saw Visual Studio, but I do believe it is a decent way to debug C code. But it sounds like it wa tough to explore the border between C and Python code, which is why it took you so long to find the issue, right?

Also, please be aware that tulip is not ready for anything. As I just stated in a thread on python-dev, it is just my way of trying to understand the issues with async I/O (in a different context than where I've understood them before, i.e. App Engine's NDB). I am well aware of how hard it is to debug currently -- just read the last section in the TODO file. I have not had to debug any C code, so my experience is purely based on using pdb. Here, the one big difficulty seems to be that it does the wrong thing when it hits a yield or yield-from -- it treats these as if they were returns, and this totally interrupts the debug flow. In the past, when I was debugging NDB, I've asked in vain whether someone had already made the necessary changes to pdb to let it jump over a yield instead of following it -- I may have to go in and develop a change myself, because this problem isn't going away.

However, I have noted that a system using a yield-from-based scheduler is definitely more pleasant to debug than one using yield -- the big improvement is that if the system prints a traceback, it automatically looks right. However there are still situations where there's a suspended task that's holding on to relevant information, and it's too hard to peek in its stack frame. I will be exploring better solutions once I get back to working on tulip more intensely.

-- --Guido van Rossum (python.org/~guido)

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