On 2008-01-08 17:57Z, Norton Allen wrote:
[snip code that times this inner loop:]
>
> for ( i = 0; i < 8; i++ ) {
> sleep(1);
> cur_time = clock();
> printf( "clock() = %ld\n", cur_time );
>
> I would expect the clock() values to increase by approximately 1000 on
> each iteration. (Yes, the sleep() seems to be working, as the lines come
> out at about 1 Hz.)
I get similar results with the same program. According to
C99 7.23.2.1/2,
"The clock function determines the processor time used."
so I'd guess that sleep() is consuming only wall-clock time.
Here's your program with an inner loop that consumes cycles:
/tmp[0]$cat clock_test.c
#include <time.h>
#include <unistd.h>
#include <stdio.h>
#include <limits.h>
int main( int argc, char **argv ) {
clock_t cur_time, cps = CLOCKS_PER_SEC;
int i, j;
volatile unsigned int v;
printf( "CLOCKS_PER_SEC = %ld\n", cps );
for ( i = 0; i < 8; i++ ) {
for ( j = 0; j < INT_MAX / 10; j++ ) {
v++;
}
cur_time = clock();
printf( "clock() = %ld\n", cur_time );
}
return 0;
}
/tmp[0]$gcc -o clock_test.exe clock_test.c
/tmp[0]$./clock_test
CLOCKS_PER_SEC = 1000
clock() = 437
clock() = 859
clock() = 1265
clock() = 1687
clock() = 2093
clock() = 2515
clock() = 2937
clock() = 3343
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