Re: LinuxThreads or other alternatives for the Hurd/{Mach,L4}?

[Michael Hohmuth]

Farid Hajji <address@hidden> writes:

> In practice the Hurd servers use quite a lot of threads. For example,
> current filesystem servers use one thread per open file and it is not
> uncommon to have mach tasks with say 250 simultaneous threads on a
> midely loaded system. Of course, this liberal usage of threads could
> be curbed in the Hurd itself, e.g. by pooling threads and limiting the
> maximum parallelism. The Hurd designers choose not to do so because
> they wanted to benefit from Mach implementations for massively
> parallel systems (that was quite a biggy back then) and they
> argumented, that a uKernel and its associated threading libraries
> should provide a very high number of threads and that it should not be
> a matter of application specific code to deal with such restrictions.

I see.

> It seems that the thread-client Hurd code should not be modified
> substantially (e.g. by pooling), but that a library should provide
> for the N:M mapping (even on systems where N >> M ). Is this realistic?

Yes, I think so.

> Hmmm... I'd prefer to leave this out at the moment and concentrate on
> real work.
> 
> It's okay to use a rather limited number threads for initial experiemnts
> though...

Yes.  However, you need to avoid the trap of becoming too tied to any
kernel-specific threading and IPC interface.  I suggest using a subset
of pthreads for threading, and an RPC mechanism to hide the coupling
between IPC and threads.

> > - Last USENIX had a paper about a Solaris-compatible thread library --
> >   <URL:http://www.usenix.org/events/usenix01/freenix01/wood.html>.
> >   Solaris has N:M threading, and the library is said to be
> >   API-compatible, but I don't know if it also implements N:M.
> Thanks for the pointers. I lost the reference of that Usenix paper
> before being able to grab it and somewhere l4-hurd already mentioned
> a pthreads library written by IBM but without providing any further
> references. That's a lot to study for the next days ;-)

BTW, the paper is also available freely at
<URL:http://opensource.compaq.com/the_source/linux_papers/scl_solaris.htm>.

Michael
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