Subj : how to use select in each thread
To   : comp.programming.threads
From : Zongjun  Qi
Date : Sun Apr 17 2005 09:40 am

I am doing a router simulation. The router gets data from several
TCP/UDP inputs, and do some processing.
My architecture is: A main thread is router, then for simulation of
each TCP/UDP flow, I create a thread. Because each TCP may have
different round-trip time, I would like to use a timer for each TCP
thread. But as I spent 4 days googling the  Linux world, the answer
seems to be only build a timer queue!
I am wondering if I can do by repeating
select(0,NULL,NULL,NULL,&tv)function in each thread. But as the my
output displays, when a thread gets its time slice, it will do select
many times(time slice>tv), and only when its time slice is over, the
next thread gets its own, and do a multiple times of select. While what
I really want to realize is their total independence.

below is the code.
---------------
/**************************************************/

#include <pthread.h>
#include <stdio.h>
#include <sys/select.h>

#define MAX_THREADS 5

int sum; /* this data is shared by the thread(s) */
  pthread_t tid[MAX_THREADS];     /* the thread identifiers  */

void *runner(void * param);

main(int argc, char *argv[])
{
  int num_threads, i;

  pthread_attr_t attr; /* set of thread attributes */
	struct sched_param sp;
	sp.sched_priority = sched_get_priority_min( SCHED_RR );

  if (argc != 2) {
    fprintf(stderr, "usage:  a.out <integer value>\n");
    exit();
  }

  if (atoi(argv[1]) <= 0) {
    fprintf(stderr,"%d must be > 0\n", atoi(argv[1]));
    exit();
  }

  if (atoi(argv[1]) > MAX_THREADS) {
    fprintf(stderr,"%d must be <= %d\n", atoi(argv[1]), MAX_THREADS);
    exit();
  }

  num_threads = atoi(argv[1]);
  printf("The number of threads is %d\n", num_threads);

  /* get the default attributes */
  pthread_attr_init(&attr);

  /* create the threads */
  for (i=0; i<num_threads; i++) {
    pthread_create(&(tid[i]), &attr, runner, (void *) i);
    printf("Creating thread number %d, tid=%lu \n", i, tid[i]);
  }

  /* now wait for the threads to exit */
  for (i=0; i<num_threads; i++) {
    pthread_join(tid[i],NULL);
  }
}

/* The thread function */
void *runner(void * param)
{
  int i;
  int ret;
  int threadnumber = (int) param;
  struct timeval tv;
  tv.tv_sec= 0;
  tv.tv_usec=100000*(threadnumber+1);
  while(1)
  {
	select(0,NULL,NULL,NULL,&tv);
  	printf("Thread number=%d\n", threadnumber);
  }
}

---------------

Any help is highly appreciated.
--
Zongjun

.