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POtime delay in C. usleep
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  1. POtime delay in C. usleep
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    copied!<p>I'm developing the game server, which is written on C. And I need to develop a cycle with a certain frequency (50 times per second) to perform an algorithm. The problem is that I can't pause the program for an exact time interval - 20000 microseconds. Function <code>usleep(20000)</code> runs about 30000 microseconds. The result is always more on 10000 microseconds than expected.</p> <p>Here is my simple example of code:</p> <pre class="lang-c prettyprint-override"><code>#include &lt;stdio.h&gt; #include &lt;time.h&gt; #include &lt;unistd.h&gt; int main( int argc, char ** argv ) { const unsigned long long nano = 1000000000; unsigned long long t1, t2; struct timespec tm; for(;;) { clock_gettime( CLOCK_REALTIME, &amp;tm ); t1 = tm.tv_nsec + tm.tv_sec * nano; usleep( 20000 ); clock_gettime( CLOCK_REALTIME, &amp;tm ); t2 = tm.tv_nsec + tm.tv_sec * nano; printf( "delay: %ld\n", ( t2 - t1 ) / 1000 ); } return 0; } </code></pre> <p>And the result of it's running:</p> <pre><code>$ ./a.out delay: 29233 delay: 29575 delay: 29621 delay: 29694 delay: 29688 delay: 29732 delay: 29709 delay: 29706 delay: 29666 delay: 29702 delay: 29702 delay: 29705 delay: 29789 delay: 29619 delay: 29785 delay: 29634 delay: 29692 delay: 29708 delay: 29701 delay: 29703 </code></pre> <p>I also tried to use function <code>select()</code>, but result is the same as with the <code>sleep()</code>.</p> <p>Explain to me, please, what's wrong with my code.</p> <p>p.s.:</p> <pre><code>$ uname -a FreeBSD home.com 9.0-RELEASE FreeBSD 9.0-RELEASE #0: Tue Jan 3 07:46:30 UTC 2012 root@farrell.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC amd64 </code></pre>
 

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