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POwhy ostringstream could not work well in multithreading environment
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  1. POwhy ostringstream could not work well in multithreading environment
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    copied!<p>Maybe something is weird. When I use STL ostringstream class in my multithreading environment I found that the execution time of each thread increased linearly as the thread number increased. I don't know why this happened. I try to check the ostringstream source code but could not find any synchronization code. Are there some synchronization place in ostringsstream? I replace ostringsstream with snprintf and the preformance increase largely. My OS is RHEL5.4 64BIT and my server has two xeon 5620 cpu on it.</p> <p>The following is the running result I use 1 and 8 thread separately with 1000000 loops. the left column is threadid and the right is running time. So it's apparant the per thread running time increase as the thread number increase.</p> <pre><code>[host]$./multi_thread 1 1000000 1115760960:0.240113 [host]$./multi_thread 8 1000000 1105004864:8.17012 1115494720:8.22645 1125984576:8.22931 1136474432:8.41319 1094252864:8.73788 1167944000:8.74504 1157454144:8.74951 1146964288:8.75174 </code></pre> <p>the code is list as below</p> <pre><code>#include &lt;iostream&gt; #include &lt;sstream&gt; using namespace std; void * func(void * t) { int n = *((int *) t); pthread_t pid = pthread_self(); timeval t1, t2; gettimeofday(&amp;t1, 0); for(int i = 0; i &lt; n; i++) { ostringstream os; /* char buf[255]; int ret = snprintf(buf, 30, "%d", 2000000); buf[ret] = 0; */ } gettimeofday(&amp;t2, 0); #define DIFF(a, b) ((b.tv_sec - a.tv_sec) + (b.tv_usec - a.tv_usec) / 1000000.0) std::cout &lt;&lt; pid &lt;&lt; ":" &lt;&lt; DIFF(t1, t2) &lt;&lt; std::endl; #undef DIFF return NULL; } int main(int argc, char *argv[]) { int m, n =0; m = atoi(argv[1]); n = atoi(argv[2]); pthread_t tid[m]; for(int i = 0; i &lt; m; i++) pthread_create(&amp;tid[i], NULL, func, &amp;n); for(int i = 0; i &lt; m; i++) pthread_join(tid[i], NULL); return 0; } </code></pre>
 

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