🚀 go-pugleaf

: >OK, try this. VMS has something called an AST (Asynchronous System Trap) which
: >is similar to a user-mode interrupt. This may occur at any time: for instance,
: >an asynchronous I/O can call an AST routine when the I/O completes. When the
: >AST routine completes, control returns to the code that was executing at the
: >time the AST occurred. (The analogy in NT is the APC, or Asynchronous
: >Procedure Call.)
: >
: >Now, much of the run-time stuff in UNIX is non-reentrant. In particular, the 
: >use of errno springs to mind. If the AST (or APC) was introduced into the
: >UNIX model, how can I use these non-reentrant routines safely in an AST
: 
: While you are at it, don't forget to include a separate 32-bit value
: passed to the AST.  The AST is fully queue'd, and if you send 32 ASTs
: before the application executes it's handler the application will still
: see ALL the ASTs with their separate 32-bit value.
: 
: If you can make this work, now port it to AIX, SunOS, Solaris, Ultrix,
: IRIX, and HP-UX.  Those are the only environments I currently would like
: it on, I'm sure there would be more within a few months.
: 
Concurrent Computer (for whom I used to work) have had AST capability
in their real-time version of Unix (based on System V) since (as
MASSCOMP) their first product shipped some ten years ago.
As I recall, error status of the I/O operation was indeed passed as a parameter
to the AST routine. It's major use was to overlap real time data input
with output to disk or whatever. ASTs could be prioritized, buffers 
locked in memory, everything that you needed to do real-time data collection.


_______________________________________________________________________________
Simon Rosenthal:  (simon@bos.locus.com)
Locus Computing Corporation
Burlington, MA 01803