concurrency program design stackless python tasklet or python thread?

Aleksandar Radulovic alex at
Tue Nov 11 17:10:26 CET 2008

Hi there,

On Tue, Nov 11, 2008 at 5:57 AM, davy zhang <davyzhang at> wrote:
> first here is my basic idea is every actor holds their own msg queue,
> the process function will handle the message as soon as the dispatcher
> object put the message in.

Using stackless, every tasklet can have a channel which it uses to communicate
with other tasklets. The tasklet is blocked until there's something on
the channel
to receive.

> This idea naturally leads me to place every actor in a separate thread
> waiting for msg

You can have actors with many separate tasklets waiting for messages, still
being relatively lightweight, meaning you can run thousands of tasklets without
serious lack of performance.

> but I found the tasklet is really a lined-up sequence , that means if
> a tasklet blocked or do some time consuming calculation, the other
> tasklets can not get the cpu slice

This is cooperative scheduling, which you can choose not to use with Stackless
(instead, use preemptive scheduling). If you determine that one particular
task is taking too much cpu, you can declaratively call stackless.schedule()
and put that task back to the scheduler queue and allow other tasks to
have a go.

> so we must design very carefully to avoid the big job for single task

That's right - with cooperative scheduling careful design is the key.

> I am just confused why the stackless python is said to be good at
> concurrency program model or just I get a wrong idea to practice?

Stackless is an extremely lightweight way into concurrent programming.
I have personally used it in few projects and i quite like how lightweight
it is and how easy it is to write concurrent programs.

On the plus side, Stackless developers have plenty of examples and
common idioms of how Stackless should be used, which I highly recommend
you to check out. You might find a solution to your problem right there
amongst the examples.

Check it all out on

a lex 13 x

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