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From: simsong@daily-bugle.media.mit.edu (Simson L. Garfinkel)
Newsgroups: comp.sys.next
Subject: speed of access methods vs. object_getInstanceVariable
Message-ID: <4755@media-lab.MEDIA.MIT.EDU>
Date: 7 Jan 91 21:47:16 GMT
Sender: news@media-lab.MEDIA.MIT.EDU
Lines: 82

I was interested as to whether it is faster to access the instance variables of an object via accessor methods or via the object_getInstanceVariable() function, so I did a test.

Here's the program:

/*
 * Time test; see if it is faster to read instance variables with
 * accessor methods or with object_getInstanceVariable...
 */

#include <objc/Object.h>

@interface MyObject:Object
{
        int     x;
}

-setX:(int)x;
-(int)getX;
@end

@implementation MyObject
-setX:(int)aX
{
        x       = aX;
        return self;
}

-(int)getX;
{
        return(x);
}

@end

int     main(int argc,char **argv)
{
        int     method;
        int     count;
        id      anX;

        if(!strcmp(argv[1],"-m")){
                method  = 1;
                argv++;
                argc--;
        }

        count   = atoi(argv[1]);

        anX     = [[MyObject alloc] init];
        [anX setX:3];

        if(method){
                while(count-->0){
                        [anX getX];
                }
        }
        else{
                while(count-->0){
                        int     x;

                        object_getInstanceVariable(anX,"x",(void **)&x);
                }
        }
        return(0);
}

Here are the results of the time testing:

daily-bugle.media.mit.edu> time ti -m 100000
1.9u 0.2s 0:02 98% 0+0k 0+0io 0pf+0w
daily-bugle.media.mit.edu> time ti 100000   
5.7u 0.2s 0:06 97% 0+0k 0+0io 0pf+0w
daily-bugle.media.mit.edu> 

Two things of interest:
1. Accessing via the method is about 3x faster than accessing via object_getInstanceVariable.
2. I can get about 20,000 accesses/second (on a 60830 NeXT).  That seems fairly good.


Anybody else have any experience with this sort of thing?

			----Simson