Le 15 janv. 09 à 23:16, Jens Bauer a écrit :
Hi all,
I just want to let you know that I discovered I did a terrible
mistake today.
In other words: you don't have to learn from your own mistakes, if
you can learn from mine. =)
I investigated this, because my rendering was choppy.
The code...
- (void)renderObject
{
}
- (void)renderAll
{
UnsignedWide us;
double time;
Microseconds(&us);
time = ((double) us.hi) * 65536.0 * 65536.0 + ((double) us.lo);
[self renderObject];
Microseconds(&us);
time = ((double) us.hi) * 65536.0 * 65536.0 + ((double) us.lo) -
time;
NSLog(@"time:%.3fms", time * 0.001);
}
..often used around 3ms for the empty method "-renderObject".
It gave me the terrible result of up to 21ms spent in the empty
method!
-So I'd like to let you know that it's sometimes good to think "do I
really need this method?"
I will be rewriting around 8 of my large files for doing some
rendering, so they will be using C-routines instead of ObjC methods,
since I'm using them in a real-time environment.
My guess is that the message dispatcher probably needs to do
something else than servicing *my* application, so I believe it's
the nature of the environment, not a bug.
Got this with Test.m:
elapsed: 7257238014 ns (7.257238 ns per call)
--------- Test.m ---------
#import <Foundation/Foundation.h>
#include <mach/mach_time.h>
@interface Foo : NSObject {
}
- (void)nop;
@end
@implementation Foo
- (void)nop {}
@end
int main(int argc, char **argv) {
Foo *foo = [[Foo alloc] init];
uint64_t delta = mach_absolute_time();
for (NSUInteger idx = 0; idx < 1000000000; idx++) {
[foo nop];
}
delta = mach_absolute_time() - delta;
[foo release];
/* convert to nano */
mach_timebase_info_data_t sTimebaseInfo;
mach_timebase_info(&sTimebaseInfo);
delta = delta * sTimebaseInfo.numer / sTimebaseInfo.denom;
fprintf(stderr, "elapsed: %qu ns (%f ns per call)\n", delta,
delta / 1000000000.0);
return 0;
}
------------------------------------
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