NetNews Usenet Archive 1992 #26/NN_1992_26.iso/spool/comp/unix/aix/11492

Internet Message Format | 1992-11-11 | 2.5 KB

Path: sparky!uunet!charon.amdahl.com!pacbell.com!ames!haven.umd.edu!darwin.sura.net!zaphod.mps.ohio-state.edu!cs.utexas.edu!ut-emx!ibmchs!auschs!awdprime.austin.ibm.com!chukran.austin.ibm.com!rudy
From: [e-mail]
Newsgroups: comp.unix.aix
Subject: Re: swap instruction in assembler?
Keywords: n
Message-ID: <[e-mail]>
Date: 11 Nov 92 17:35:52 GMT
References: <[e-mail]> <[e-mail]>
Sender: [e-mail] (USENET News)
Reply-To: [e-mail](Rudy Chukran)
Organization: IBM Advanced Workstation Division
Lines: 33

In article <[e-mail]>, [e-mail] (Jeff Peek) writes:
|> The hardware doesn't have a test-and-set instruction available. However,
|> the operating system has implemented in AIX 3.2 a fast SVC called cs().
|> The prototype is int cs(int *, int, int). This does cause a "trap" to the
|> OS, but this code is fast pathed through the system call handler and is
|> coded in a few assembler instruction that will atomically do the operation.
|> As long as the address passed is not misaligned, there should be no problem.
cs has been there since AIX 3.1, if anybody cares. However, to put in a "plug"
for an interface new in AIX 3.2:

If you need a light weight semaphore, Id suggest also looking into the
msem_lock binary semaphore interface.  It uses cs to set the lock word
in shared memory. It will block if the word is already locked.
Measurements show that msem_lock is 30 times faster than semop when the
semaphore isnt already locked (uncontended case).

Otherwise, the process which contends the lock must do something. If it
it should do some useful processing, then do it. If it must sleep, then
Id recommend using the msem_lock. It is the most efficient on AIX for
multiple waiters.

Im just trying to get the word out about a little known interface that
is new to AIX 3.2 that solves a very specific problem with fast
process syncronization.  The set of interfaces to look up are
msem_init, msem_lock, msem_unlock.
--
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Rudy Chukran                |       EMAIL:
IBM AIX Technical Consulting| RSCS: CHUKRAN at AUSTIN
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