[Stackless] "Attempt to run a locked frame!"

Gordon McMillan gmcm at hypernet.com
Tue Feb 20 14:35:33 CET 2001

Well after modifying Bernd's code so it works with 1.5.2 
stackless (and an older uthreads that does not have "wait"), I 
can report that it runs fine. I simply commented out the 
uthread.wait and used delay as the select timeout.

BTW, a hostname of '' means INADDR_ANY, which is not the 
same as "localhost". For the client, at least, I think you want 
"localhost" - Windows won't connect to '' (while macs don't 
even recognize "localhost" as a special name!).

> On Mon, Feb 19, 2001 at 07:55:23PM -0500, Gordon McMillan wrote:
> > [...] What's probably going on is either (1) trying to use a >
> continuation from a recursive invocation of Python or (2) trying
> > to use a plain callable object as a continuation. > > You could
> hit (1), for example, by trying to use a continuation > within a
> __getitem__ (or other magic method). This is > implemented by C
> code that realizes it needs to execute pure > Python, so
> recursively invokes the interpreter. But if that pure > Python
> tries to use a continuation created in an outer > invocation of
> the interpreter, it would trash the C stack. So, it's > streng
> verbotten. [...]
> Does "use a continuation" include an automatic task switch
> performed by the uthread module? And as a consequence: are magic
> methods written in Python generally a bad idea when using
> microthreads? I do not use continuations directly but only the
> uthread module. What actions in uthreaded programs could trigger
> (1) or (2)?
> More generally: Is there somewhere a list of do's and dont's when
> using microthreads? 
> I have written a metathread package to encapsulate differences
> between threads und uthreads and a multithreaded server framework
> that makes use of it (python remote procedure calls) and I want
> to make it freely available to the Python community very soon. It
> has been a nice amount of work and I really want to get it out of
> the door. Unfortunately the "Attempt to run a locked frame!"
> exception crashes each and any prpc-session when using
> microthreads instead of Python threads.
> > BTW, your sample code neglected to say what module was 
> > what, so I didn't bother to try it.
> Oh, I am sorry about that. So here are the explanations:
> * comm.py contains functions to perform socket operations in a
>   non-blocking way (when using microthreads), such as accept() or
>   send(). The core function of this module is nbselect() which
>   substitutes select.select() from the Python Libarary. So if 's'
>   is a socket you do not call 
>     s.send(buffer) 
>   but instead 
>     comm.send(s, buffer)
>   (BTW: the nbselect() in connect() is rubbish.)
> * socketFile.py defines a class socketFile that is instantiated
> with a
>   socket 'sock' and a mode (either readMode or writeMode). It is
>   used to transmit Python data objects over a socket by means of
>   pickling and unpickling. To transmit an object 'x', you do:
>   Sender:
>   -------
>   f = socketFile.socketFile(sock, socketFile.writeMode)
>   cPickle.dump(x, f)
>   f.send()
>   Receiver:
>   ---------
>   f = socketFile.socketFile(sock, socketFile.readMode)
>   x = cPickle.load(f)
> * miniserver.py spawns a uthreaded server that is listening on
> 'PORT'
>   (which is set to 50000). It consists of (1) serverloop() which
>   accept()s new connections and (2) handle() which handles the
>   connection requests. serverloop() spawns a new microthread for
>   each connection running the function handle() therein.
> * miniclient.py makes a connection to port 'PORT' on localhost
> and
>   causes some network traffic in a loop. It transmits trash to
>   the server and receives a list of active connections. Finally
>   it sends a 'None' to finish the connection.
> When I start one miniserver and one miniclient everything works
> well. As soon as I start two miniclients in parallel, the server
> bombs with the exception
> SystemError: Attempt to run a locked frame!
> Since I am not familiar with continuations I see no way to track
> down that bug myself. I ask myself, if it bites other uthread
> users as well...
> Bernd
> -- 
> Bernd Rinn
> Fakultät für Physik
> Universität Konstanz
> Tel. 07531/88-3812, 
> e-mail: Bernd.Rinn at uni-konstanz.de
> PGP-Fingerprint: 1F AC 31 64 FF EF A9 67  6E 0D 4C 26 0B E7 ED 5C
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- Gordon
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