[Tutor] sockets, files, threads

[Danny Yoo]

On Wed, 12 Jan 2005, Marilyn Davis wrote:

> When stuff was read from the exim socket, it was stored in a tempfile,
> so that I could release the exim process, then I lseek to the front of
> the tempfile and have it handy.  I see from all my debugging and logging
> that the file descriptor for this tempfile is 9.

Hi Marilyn,

Question: do you really need to use a tempfile?  If your daemon is
persistent in memory, can it just write to a StringIO object?

StringIO.StringIO elements act like files too, and may be easier to
maintain than a tempfile.TemporaryFile.  If you can show us how you're
constructing and using the TemporaryFile, we can try to trace any
problematic usage.


> The program then opens a pipe to exim to send mail.  I see that the
> popen2.popen3 call returns 9 for the stdin file descriptor for the pipe.
>
> The tempfile (also file descriptor 9) is read for piping into exim and
> it errors with "Bad file descriptor".

Oh!  This situation sounds like the 'tempfile' is being closed at some
point, releasing the file descriptor back to the system.  If that is what
is happening, then that's why the pipe has the same descriptor id: the
call to pipe() just reuses a free file descriptor.

I'd look for places where the tempfile might be close()d.  I'd also look
for places where your reference to tempfile is reassigned, since that
would also signal a resource collection.



> Worse yet, the first 5 messages of my test go through the entire process
> without a problem, and then # 6 hits this -- but only if # 1 message is
> really big.

Just double checking something: are you dealing with threads?


Best of wishes to you!