threads blocked during import?

[Mark Hammond]

Geoff Talvola wrote:

> I was wondering the other day: if two threads try to import the same 
> module at the same time, what happens?  I wrote a test program, and it 
> looks like an import blocks all other threads from importing.  This is 
> probably a good thing, since you only want the module to be imported once.
> 
> Here's the test program, and the helper module that it imports.  Running 
> it on my WinNT box shows that the 2nd thread to try to import the module 
> blocks while the first thread is importing it, and the module doesn't 
> get imported twice.  That's a good thing.
> 
> My question for the gurus is, can I count on this locking taking place, 
> and put code that absolutely needs to run only once at module level 
> without any special locking?

Yes.  The Python win32com support actually discovered Python had a bug 
in this area, so Guido added an explicit lock just for this case.

Mark.