On Wed, 5 May 1999 08:37:33 +1000, Richard Gooch <rgooch@atnf.csiro.au>
said:
>> Ugh. I liked the VMS model here. When you queue an I/O request,
>> one of the things you can attach to it is the address of a
>> procedure. When the request completes, the kernel creates a
>> temporary thread to execute the I/O rundown code, and part of that
>> rundown is to call the procedure you supplied.
> What was the cost of creating the "temporary thread"?
There isn't one: the AST is scheduled in the context of the calling
process/thread. AST delivery is an integral part of the scheduler, much
like signal delivery is on Unix.
> Anyway, we can do much the same thing with signals, except we don't
> need to create a temporary thread.
Yes --- ASTs are very similar to posix.4 queued signals.
--Stephen
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