Coroutines [was Re: threading question]

[Russell Leighton <russell.leighton@247media.com>]

Any chance this or the equiv could become part of glibc?

This seems a very handy abstraction,  in many apps
threads would then really only be needed for true parallelism.


Michael Rothwell wrote:

> Try this:
>
> http://lecker.essen.de/~froese/coro/
>
> -M
>
> On 16 Jun 2001 14:33:50 -0400, Russell Leighton wrote:
> >
> > Is there a user-space implemenation (library?) for coroutines that would work from C?
> >
> >
> > Alan Cox wrote:
> >
> > > > Can you provide any info and/or examples of co-routines? I'm curious to
> > > > see a good example of co-routines' "betterness."
> > >
> > > With co-routines you don't need
> > >
> > >         8K of kernel stack
> > >         Scheduler overhead
> > >         Fancy locking
> > >
> > > You don't get the automatic thread switching stuff though.
> > >
> > > So you might get code that reads like this (note that aio_ stuff works rather
> > > well combined with co-routines as it fixes a lack of asynchronicity in the
> > > unix disk I/O world)
> > >
> > >         select(....)
> > >
> > >         if(FD_ISSET(copier_fd))
> > >                 run_coroutine(&copier_state);
> > >
> > >         ...
> > >
> > > and the copier might be something like
> > >
> > >         while(1)
> > >         {
> > >                 // Yes 1 at a time is dumb but this is an example..
> > >                 // Yes Im ignoring EOF for this
> > >                 if(read(copier_fd, buf[bufptr], 1)==-1)
> > >                 {
> > >                         if(errno==-EWOULDBLOCK)
> > >                         {
> > >                                 coroutine_return();
> > >                                 continue;
> > >                         }
> > >                 }
> > >                 if(bufptr==255  || buf[bufptr]=='\n')
> > >                 {
> > >                         run_coroutine(run_command, buf);
> > >                         bufptr=0;
> > >                 }
> > >                 else
> > >                         bufptr++;
> > >         }
> > >
> > > it lets you express a state machine as a set of multiple such small state
> > > machines instead.  run_coroutine() will continue a routine where it last
> > > coroutine_return()'d from. Thus in the above case we are expressing read
> > > bytes until you see a new line cleanly - not mangled in with keeping state
> > > in global structures but by using natural C local variables and code flow
> > >
> > > Alan
> > >
> > > -
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> >
> > --
> > ---------------------------------------------------
> > Russell Leighton    russell.leighton@247media.com
> > ---------------------------------------------------
> >
> >
> > -
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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> --
> Michael Rothwell
> rothwell@holly-springs.nc.us



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Russell Leighton    russell.leighton@247media.com
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