Can't connect to MySQL server on 'localhost' (111)

Question

I am developing a threaded program which reads a mysql database in 10 threads and print the result as a row count by each thread. So the final result is 100 line counts on the command line. the problem is when I run it it sometimes gives an error saying Can't connect to MySQL server on 'localhost' (111) sometimes it returns a segmentation fault(core dumped) I checked the threads and they are also created fine with no errors.

when I create only one thread it works perfectly fine giving the expected output. No of Rows of 00 - 6

Another thing is I run this in a red hat server and It works well with no errors but the count is wrong.I created 5 threads and for the first thread 52380 is correct but for others it gives a different result the result should come like this

No of Rows  of 00 - 52380
No of Rows  of 01 - 53434
No of Rows  of 02 - 53333
No of Rows  of 03 - 50005
No of Rows  of 04 - 48393

but the actual result coming out is this

No of Rows  of 00 - 52380
No of Rows  of 00 - 52380
No of Rows  of 01 - 52380
No of Rows  of 01 - 52380
No of Rows  of 01 - 52380

I compile this using

gcc main.c -lpthread `mysql_config --cflags --libs`

What would be the cause for this problem. Can anyone help me with this please. Down here is the code I used. Header file is not given here. It contains the database details.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "main1.h"
#include <pthread.h>
#include <mysql/mysql.h>
#include <mysql/my_global.h>

int main(int argc, char** argv) {

   int threadRet[10], i = 0;
   pthread_t * threadT = (pthread_t *) malloc(10 * sizeof (pthread_t));

   for (i = 0; i < 10; i++) {
        threadRet[i] = pthread_create(&threadT[i], NULL, threadedConnection, &i);
        printf("thread %d - thread ret %d\n",i,threadRet[i]);
   }
   i = 0;
   for (i = 0; i < 10; i++) {
        pthread_join(threadT[i], NULL);
   }
   return (EXIT_SUCCESS);
 }



void * threadedConnection(void * parr) {

    int * j = (int *) parr;
    int tableNo=*j;
    long int rowCount = 0;
    long int totalInserts = 0;

    MYSQL *con1 = mysql_init(NULL);
    MYSQL_RES *result;
    MYSQL_ROW row;
    con1[tableNo] = mysql_init(NULL);
    if (mysql_real_connect(con1, dataBase1[0], dataBase1[1], dataBase1[2], dataBase1[3], 0, NULL, 0) == NULL) {
        fprintf(stderr, "%s\n", mysql_error(con1));
        mysql_close(con1);
        exit(1);
     }

     char countQuery[70];
     sprintf(countQuery, "SELECT COUNT(*) FROM numberTable where number like '%s%.2d'", "%", *tableNo);

     if (mysql_query(con1[tableNo], countQuery)) {
        fprintf(stderr, "%s\n", mysql_error(con1));
        mysql_close(con1);
        exit(1);
     }

     result = mysql_store_result(con1);       //Counting
     row = mysql_fetch_row(result[tableNo]);  //line
     rowCount = strtol((row)[0], NULL, 10);   //numbers
     totalInserts = rowCount;                 //numberTable
     mysql_free_result(result[tableNo]);

     printf("No of Rows  of %.2d - %ld\n", tableNo, totalInserts);



     mysql_close(con1[tableNo]);
     }

Answer 1

I had to go throgh a really tough situation to finally get to the point. It was so simple that Only a single array declaration would do the thing. In my code , in the main function. when creating threads I've used,

for (i = 0; i < 10; i++) {
    threadRet[i] = pthread_create(&threadT[i], NULL, threadedConnection, &i);
    printf("thread %d - thread ret %d\n",i,threadRet[i]);
}

Here is anthor link which says about this Pthreads

the thing is that when the arrays do their work they uses the passed integer i and since the address of the integer is passed and in the for loop it continuously increases its value . So when threads try to use it its already incremented and continuously increased. so it gets jammed.

So to overcome it what I did was I declared an array

 for (i = 0; i < threadCount; i++) {
    tbl[i] = i;
 }
 i == 0;

and this arrays elements were passed when creating the threads as

 for (i = 0; i < 10; i++) {
    threadRet[i] = pthread_create(&threadT[i], NULL, threadedConnection, &tbl[i]);
    printf("thread %d - thread ret %d\n",i,threadRet[i]);
 }

this did the work well. And there were also some fewer modifications. that I didn't mention here because I believe they are not related to my problem. they are when joining threads in the end of the main , I used a pthread_attr to make them joinable other wise it wasn't quite right . so here is the final code only the (main function is given here since changes were taken place only in the main)

int main(int argc, char** argv) {

    int threadRet, i = 0;
    int tbl[threadCount];
    void *status;
    pthread_attr_t attr;

    for (i = 0; i < threadCount; i++) {
    tbl[i] = i;
    }
    i == 0;

    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

    pthread_t * threadT = (pthread_t *) malloc(threadCount * sizeof (pthread_t));

    for (i = 0; i < threadCount; i++) {
    threadRet = pthread_create(&threadT[i], &attr, threadedConnection, &tbl[i]);
        if (threadRet) {
            printf("Error creating thread return value of pthread_create() is %d", threadRet);
        }
        printf("thread %d - thread ret %d\n", i, threadRet);
    }
    i = 0;

    pthread_attr_destroy(&attr);

    for (i = 0; i < threadCount; i++) {
        threadRet = pthread_join(threadT[i], &status);
        if (threadRet) {
            printf("Error joining thread return value of pthread_join() is %d", threadRet);
        }

    }

    free(threadT);
    pthread_exit(NULL);
    return (EXIT_SUCCESS);
}

thanks anyone who tried to help out contributing their time....

Answer 2

In

if (mysql_real_connect(con1, dataBase1[0], dataBase1[1], dataBase1[2], dataBase1[3], 0, NULL, 0) == NULL) {
          ^ port

You need to pass the port which is default to 3306. Check for the host name and other parameter.

See http://dev.mysql.com/doc/refman/5.7/en/mysql-real-connect.html for reference.