Re: For the AdaOS folks

["Warren W. Gay VE3WWG" <ve3wwg@NoSPAM.cogeco.ca>]

Nick Roberts wrote:
> "Warren W. Gay VE3WWG" <ve3wwg@NoSpam.cogeco.ca> wrote:
>>Mach's migrating threads do in fact cross into other "tasks". Instead of a
>>caller thread stopping when a message is queued, and the receiving thread
>>starting (from a blocked state), a migrating thread continues from the
>>caller, works through the server code, and then returns back to the caller
>>(in the caller's "task"). This is a simplification of what happens,
>>because there are "activations" and stack games that must happen to make
>>this work - but it is a migrating thread.
> 
> I'm not quite sure what you're getting at, Warren. I don't think it's very
> surprising that Mach has capabilities that are similar to Bachar, since they
> are both aimed at doing roughly the same thing. But there are significant
> differences in the details. I did begin designing (what has become) Bachar a
> long time ago (pre-1990s).

Mach's roots go back to 1975, which is quite some time ago ;-)

>>>>But if you look at the Mach paper above, you can do the very same
>>>>thing with ports. Even without thread-migration, you can interpose
>>>>proxies. With thread-migration enabled RPC, you achieve both and
>>>>provide the OS designer a nicer interface.
>>>
>>>But if we did that, what would be the advantage?
>>
>>Its cheaper. To have 1000 send rights, costs near nothing. 1000 send
>>rights in one task costs nothing (just increments ref count). 1000 in a
>>1000 different tasks, costs one pointer in each task. Nothing further.
>>
>>1000 threads OTOH, costs you state information for each of those 1000
>>threads (same task or different). The amount of state information needed
>>will vary with platform.
> 
> I have to guess somewhat, Warren, at the point you are making (maybe it's my
> fault). Are you suggesting that if I have 1000 client processes (or
> threads?) performing trans-network IPC, it will be necessary to have 1000
> (or 2000?) proxy processes (or threads)? On AdaOS, in practice, there will
> only be one proxy process (the program Avarus, running once on each
> workstation).

However, the "name service" for example, will often have many clients
(only one receive port for the name service, but at least one send-right
for every client "task" on the system). This is one example where
the numbers of send-rights can be large.
-- 
Warren W. Gay VE3WWG
http://home.cogeco.ca/~ve3wwg