[coyotos-dev] Re-thinking FCRBs

[Marcus Brinkmann]

At Thu, 15 Feb 2007 14:15:19 -0500,
"Jonathan S. Shapiro" <shap at eros-os.com> wrote:
> ** So what about asynchronous *sends* ??
> 
> If we need a mechanism for asynchronous completion, what about a
> mechanism for asynchronous sends?
> 
> My answer is "no". If the use of asynchronous receive is properly
> engineered, sends will not block. If they do you have a systemic issue
> and my sense is that you want to see it rather than obscure it. I could
> be completely wrong on this, and I'ld appreciate input on this point.

I have only come up with one use case for asynchronous send.  It's the
case where one does not want to allocate a stall queue in the server
for "blocking" RPCs like reading from an empty pipe (which is a
read-only operation and presumably should not allocate server
resources).  In principle, it is not clear why the server should need
to allocate a queue for such client operations, as there already is a
kernel queue that could be used for this purpose. However, pushing a
client back to a send() operation on an end point that the server is
not listening on (until the operation can potentially be completed)
makes send() a blocking operation.

Thanks,
Marcus