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PODoes Linux Time Division Processes Or Threads
 

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    <p>A prof once told us in class that Windows, Linux, OS X and UNIX scale on threads and not processes, so threads would likely benefit your application even on a single processor because your application would be getting more time on the CPU.</p> <p>I tried with the following code on my machine (which only has one CPU).</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; #include &lt;pthread.h&gt; pthread_t xs[10]; void *nop(void *ptr) { unsigned long n = 1UL &lt;&lt; 30UL; while(n--); return NULL; } void test_one() { size_t len = (sizeof xs) / (sizeof *xs); while(len--) if(pthread_create(xs+len, NULL, nop, NULL)) exit(EXIT_FAILURE); len = (sizeof xs) / (sizeof *xs); while(len--) if(pthread_join(xs[len], NULL)) exit(EXIT_FAILURE); } void test_two() { size_t len = (sizeof xs) / (sizeof *xs); while(len--) nop(NULL); } int main(int argc, char *argv[]) { test_one(); // test_two(); printf("done\n"); return 0; } </code></pre> <p>Both tests were identical in terms of speed.</p> <pre><code>real 0m49.783s user 0m48.023s sys 0m0.224s </code></pre> <p></p> <pre><code>real 0m49.792s user 0m49.275s sys 0m0.192s </code></pre> <p>This me think, "Wow, threads suck". But, repeating the test on a university server with four processors close to quadrupled the speed.</p> <pre><code>real 0m7.800s user 0m30.170s sys 0m0.006s </code></pre> <p></p> <pre><code>real 0m30.190s user 0m30.165s sys 0m0.004s </code></pre> <p>Am I overlooking something when interpreting the results from my home machine?</p>
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    1. COThe saying is that "In UNIX you're better of using processes and not threads for IPC", that is not necessarily because the threading model is worse - though it is - or so I'm told. But, because the process model is massively better, and more lightweight. When it comes to IPC, it is a lot easier to get the process model right and stable than the threading model. And, when you have copy-on-write and other niceties the advantages favor forking. I'm only parroting this because something you heard triggered the question - and I think you misheard what I'm describing.
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