Thread: Questions about pthreads

Hey, I am starting to mess around with the libpthreads implementation on GNU/Linux. I do not understand why for instance, when I use pthread_create() to create threads, sometimes, no threads are created. To even see any output from threads whatsoever I have to literally create hundreds of threads. No matter how many I create, there always seems to be an inconsistent amount being created. Here is some of my code that demonstrates these problems I am having.

Code:

   #include <stdio.h>
 #include <string.h>
 #include <time.h>
 #include <stdlib.h>
 #include <pthread.h>
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <errno.h>
 

 

 void usage(char *);
 

 void *net_thread(void *);
 

 FILE *glob_file;
 

 int glob_port;
 

 int main(int argc, char *argv[])
 {
     int numthreads, rc;
     long i;
 

     srand(time(NULL));
     if(argc != 4)
         usage(argv[0]);
     
     glob_port = atoi(argv[1]);
     numthreads = atoi(argv[2]);
     unsigned long *taskids[numthreads];
     pthread_t thread_array[numthreads];
 

     glob_file = fopen(argv[3], "w+");
 

     // generate array of random ip addresses
     for(i = 0; i <= numthreads; i++)
     {
         taskids[i] = (long *) malloc(sizeof(long));
         *taskids[i] = i;
         rc = pthread_create(&thread_array[i], NULL, net_thread, (void *) taskids[i]);
     }
     return 0;
 }
 

 void usage(char *progname)
 {
     fprintf(stderr, "Usage: %s <port> <numthread> <output file>\n", progname);
     exit(1);
 }
 

 void *net_thread(void *thr_arg)
 {
     int sockfd;
     unsigned long connip;
     unsigned int a, b, c, d;
     struct sockaddr_in mysock;
     char str_ip[30];
 

     connip = (rand()) * (long) (thr_arg);
 

     // separate bytes in connip
 

     a = (connip >> 24 & 0xFF);
     b = (connip >> 16 & 0xFF);
     c = (connip >> 8 & 0xFF);
     d = (connip & 0xFF);
 

 

     printf("from thread: %X\tdotted notation: %d.%d.%d.%d\n", connip, a, b, c, d);
 

     if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1){
         perror("socket");
         pthread_exit(NULL);
     }
 

     snprintf(str_ip, sizeof(str_ip), "%d.%d.%d.%d", a, b, c, d);
 

     bzero(&mysock, sizeof(mysock));
 

     mysock.sin_family = AF_INET;
     mysock.sin_port = htons(glob_port);     // short, network byte order
     mysock.sin_addr.s_addr = htonl(connip);
 

     if((connect(sockfd, (struct sockaddr *) &mysock, sizeof(mysock))) == -1){
         switch(errno){
             case ECONNREFUSED:
                 fprintf(glob_file, "Port %d Closed on %s\n", glob_port, str_ip);
                 break;
             default:
                 break;
         }
         pthread_exit(NULL);
     }
     /* connection succeeds */
     else{
         fprintf(glob_file, "Port %d Open on %s\n", glob_port, str_ip);
         pthread_exit(NULL);
     }
     
     pthread_exit(NULL);
 }