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Re: Non-system asyncs

From: Tom Lord
Subject: Re: Non-system asyncs
Date: Thu, 10 Oct 2002 01:05:39 -0700 (PDT)

    >> [...]  But I still don't see
    >> what the point of non-system asyncs is

Asyncs (both "system" and "non-system") are a mechanism for scheduling 
asychronously invoked computation that can not be explained by the 
semantics of ordinary evaluation.

My program is running along and, all of the sudden, out of the blue,
some function is invoked whose invocation can't be explained by the
source of the procedure being run at the time.   That's an async.

It's a partial alternative to threads for single-CPU applications.

System interrupts are well-described by asyncs.  Oops -- I got SIGHUP
-- run the SIGHUP handler.

But why does the kernel get to define the set of asyncs?   Why not
also have "synthetic asyncs"?   It's a way to say to the
implementation: "here's a computation that you should run as soon as
you can, regardless of whatever else is going on".

One might do incremental display updating that way, for example.


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