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From: Greg Bond <bond@ee.ubc.ca>
Subject: Re: Tips for realtime embedded Ada?
Date: 1996/04/23
Message-ID: <317D39D6.4F3@ee.ubc.ca>#1/1
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references: <4ku9jf$b7u@hacgate2.hac.com> <4l54f0$sg0@fred.netinfo.com.au>
 <4lgtnk$jm9@rational.rational.com>
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organization: Dept. of Electrical Eng., UBC
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Date: 1996-04-23T00:00:00+00:00
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Bob Kitzberger wrote:
> 
> Alan Brain (aebrain@dynamite.com.au) wrote:
> 
> : 1) Don't use Tasking except as a Guardian of resources. Very few
> : compilers do context-switching efficiently. Write a scheduler in
> : assembler, or if you can, microcode.
> 
> I would suggest that you first check the PIWG tasking benchmark
> results, and study the vendor's documentation on tasking, before
> throwing out the baby with the bathwater.  "Passive tasking
> optimizations", performed by some vendors, can reduce context
> switching time by an order of magnitude, to the level of
> user-written semaphore-protected regions.  Being able to specify
> concurrent behavior at the language level is very useful, so
> make sure you know what you're giving up, and why, before you
> run off and write your own scheduler.

<stuff deleted>

In fact, Ada 95's protected objects (like Posix..4a monitors/condition 
variables only better) can be implemented so that they they involve 
fewer lock/unlock operations, and fewer context switches than an 
equivalent semaphore-based implementation. In addition, if priority 
ceiling locking is used (also Posix.4a/Ada 95), lock/unlock operations 
do not have to use queueing which further improves performance.

---
* Greg Bond                         * Dept. of Electrical Eng.  
* email: bond@ee.ubc.ca             * Univ. of British Columbia      
* voice: (604) 822 0899             * 2356 Main Mall                 
* fax:   (604) 822 5949             * Vancouver, BC              
* web: http://www.ee.ubc.ca/~bond   * Canada, V6T 1Z4