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POlibmysqlclient race condition
 

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    <p>I have multiple threads that need to connect to a single instance of MySQL server. If every thread creates and handles its own connection everything works out as expected. I wanted to implement a simple connection pool as this :</p> <pre><code>void query_user(MYSQL* conn) { mysql_thread_init(); std::ostringstream query; query &lt;&lt; "select * from user u where u.username = '" &lt;&lt; "stack" &lt;&lt; "'"; if (mysql_query(conn, query.str().c_str())) { fprintf(stderr, "%s\n", mysql_error(conn)); exit(-1); } MYSQL_RES* res = mysql_use_result(conn); MYSQL_ROW row; while ((row = mysql_fetch_row(res)) != NULL) { printf("%s %s %s %s %s %s %s %s %s\n", row[0], row[1], row[2], row[3], row[4], row[5], row[6], row[7], row[8]); } mysql_free_result(res); mysql_thread_end(); } #define POOL_SIZE 2 int main(int argc, char** argv) { mysql_library_init(argc, argv, NULL); // Create Connection pool MYSQL* connection_pool[POOL_SIZE]; for (size_t i = 0; i &lt; sizeof(connection_pool)/sizeof(MYSQL*); ++i) { connection_pool[i] = mysql_init(NULL); if (!mysql_real_connect(connection_pool[i], server, user, password, database, 0, NULL, 0)) { fprintf(stderr, "%s\n", mysql_error(connection_pool[i])); exit(-1); } } // Thread Pool pthread_t thread_pool[POOL_SIZE]; for (size_t i = 0; i &lt; sizeof(thread_pool)/sizeof(pthread_t); ++i) { pthread_create(&amp;thread_pool[i], NULL, reinterpret_cast&lt;void* (*)(void*)&gt;(query_user), (void*)&amp;connection_pool[i]); } // join threads for (size_t i = 0; i &lt; sizeof(thread_pool)/sizeof(pthread_t); ++i) { pthread_join(thread_pool[i], NULL); mysql_close(connection_pool[i]); } mysql_library_end(); return 0; } </code></pre> <p>I have a bus error in mysql_real_query</p> <p>Could you please point out what's wrong with it ? Are there still some benefits from connection pooling ?</p> <p>I'm linking against libmysqlclient_r which is supposed to be thread safe</p> <p>Thanks,</p>
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