Path: utzoo!utgpu!cunews!cognos!jimp
From: jimp@cognos.UUCP (Jim Patterson)
Newsgroups: comp.lang.eiffel
Subject: Re: Exceptions and Assertions
Keywords: eiffel exceptions assertions preconditions
Message-ID: <8835@cognos.UUCP>
Date: 24 Sep 90 17:25:46 GMT
References: <1990Sep7.032121.6456@bony1.uucp> <14831@yunexus.YorkU.CA> <731@tetrauk.UUCP> <410@eiffel.UUCP>
Reply-To: jimp@cognos.UUCP (Jim Patterson)
Organization: Cognos Inc., Ottawa, Canada
Lines: 41

In article <410@eiffel.UUCP> kimr@eiffel.UUCP (Kim Rochat) writes:
>In article <731@tetrauk.UUCP>, rick@tetrauk.UUCP (Rick Jones) writes:
 >> >| [paraphrased]: should Eiffel programs generally be run with pre-condition
 >> >| checking on? - yes! yes! yes!
 >> 
 >> 
 >> The most effective run-time (i.e. C compile-time) option would be to
 >> check pre-conditions, void references, "check" clauses (my preference),
 >> but omit history tracing.  This means that spurious setjmp() calls are
 >> avoided, and a longjmp() in the case of an exception will go direct to
 >> the currently effective rescue handler.  This all seems possible with a
 >> little re-arrangement of the _eiffel.h file;  any comments from ISE,
 >> please?
>
>I'd like to thank Rick for this suggestion.  We've been trying to
>figure out a way to reduce the cost of assertion monitoring, but had
>been assuming that a full exception history trace was a requirement.
>If you are willing to do without the full history trace, this message
>contains a work-around which reduces the time to execute a program
>which monitors assertions by a factor of 10.

There's no reason that setjmp() has to be used to implement an
exception history trace. A small amount of inline setup code in each
function is sufficient to provide a trace history, and gives a
significant performance boost over setjmp (which is a very expensive
library call as such things go).

The basic technique is to allocate an Eiffel "call frame" in each
function which contains the class and routine numbers and a back link
to the previous function. The setup logic initializes the call frame
and links it to the previous frame; exit code unlinks (pops off) the
call frame.

This does require changing the Eiffel compiler and runtime, however,
so isn't as simple as just modifying the _eiffel.h header.

-- 
Jim Patterson                              Cognos Incorporated
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