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/* CopyRight GPL 2004 mmc Mike Chirico mchirico@comcast.net
   Created: Tue Apr 20 21:50:02 EDT 2004

   This program demonstrates the use of threads, and 
   mimics the waitpid function used by processes, plus
   it uses a dlopen call


   Compile:
   gcc  -rdynamic -o thread_join_wait_dlopen thread_join_wait_dlopen.c -ldl -lpthread 

   Download: (or check for latest version of threads_x.x.x)
   http://prdownloads.sourceforge.net/cpearls/threads_0.0.2.tar.gz?download




*/

#include <pthread.h>
#include <stdio.h>
#include <unistd.h> /* for sleep */

#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>

#define MAX_THREADS 12
#define MIN_BASE_PRNT 10
pthread_mutex_t ndone_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t  ndone_cond  = PTHREAD_COND_INITIALIZER;
int ndone;

struct t_id {
  int order;
  int prnt;
  float cval;
  char c;
  pthread_t t;
  int FLAG;
};




void* f1 (void *vt_idptr)
{ int i,max;
 struct t_id *t_idptr;
 char c;


  void *handle;
  double (*cosine)(double);
  char *error;



 t_idptr= (struct t_id *) vt_idptr;
  
 max= t_idptr->prnt;
 c = t_idptr->c;

 for(i=0; i < max; ++i)
   fputc (c, stderr);





  handle = dlopen ("libm.so", RTLD_LAZY);
  if (!handle) {
    fprintf (stderr, "%s\n", dlerror());
    exit(1);
  }


  dlerror();    /* Clear any existing error */
  *(void **) (&cosine) = dlsym(handle, "cos");
  if ((error = dlerror()) != NULL) {
    fprintf (stderr, "%s\n", error);
    exit(1);
  }

  printf ("cos(%f) = %f\n",t_idptr->cval, (*cosine)( t_idptr->cval  ));
  dlclose(handle);






    pthread_mutex_lock(&ndone_mutex);
    t_idptr->FLAG=1;
    ndone++;

    pthread_cond_signal(&ndone_cond);
    pthread_mutex_unlock(&ndone_mutex);

 return (t_idptr);
}


int main ()
{

  pthread_t t;
  int i;
  int count=0;
 
  struct t_id  t_id[MAX_THREADS];
  struct t_id *t_idptr;  /* t_idptr is needed because each thread must update */

  /* This contains data for each thread. Each thread will get its own value in the array */
  for(i=0; i< MAX_THREADS; ++i){
    t_id[i].FLAG=0;
    t_id[i].prnt=MIN_BASE_PRNT+i;
    t_id[i].order=0;
    t_id[i].cval = 3.141/((float)i + 0.2) ; /* some systems bomb on div 0 */
    t_id[i].c='a'+i;
  }
  ndone=0;

  for(i=0; i< MAX_THREADS; ++i){
   if( pthread_create (&t, NULL, &f1, &t_id[i]) != 0 )  /* Note address of t_id[i] is passed */
     {
     fprintf(stderr,"error pthread create \n");
     return 1;
     }
    t_id[i].t=t;
  }



  /* It's ok if all the threads speed through. In that case, this while
     loop will only be executed once.

     However, if you put a sleep  */
  
  while(count < MAX_THREADS ) {
    if( pthread_mutex_lock(&ndone_mutex) != 0 )
       fprintf(stderr,"error in pthread_mutex_lock \n");
    fprintf(stderr," ndone=%d \n",ndone);
    while(ndone == 0)
      if ( pthread_cond_wait(&ndone_cond, &ndone_mutex) != 0 )
	fprintf(stderr,"error in pthread_cond_wait\n");


    for(i=0; i < MAX_THREADS; ++i) {
      if( t_id[i].FLAG == 1) {
	if ( pthread_join(t_id[i].t,(void **) &t_idptr) != 0 )
	  fprintf(stderr,"pthread_join");


	fprintf(stderr," i = %d\n",i);	
	if ( &t_id[i] != t_idptr) {
	  fprintf(stderr,"t_id not matching t_idptr in final call: %d\n",count);
          return 1;
	}

	   t_id[i].FLAG = 2;
	   t_id[i].order= count++;
           ndone--;
	   fprintf(stderr," done for flag %d\n",i);
        }
    }
    pthread_mutex_unlock(&ndone_mutex);
  }

  return 0;
}




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Chirico img Mike Chirico, a father of triplets (all girls) lives outside of Philadelphia, PA, USA. He has worked with Linux since 1996, has a Masters in Computer Science and Mathematics from Villanova University, and has worked in computer-related jobs from Wall Street to the University of Pennsylvania. His hero is Paul Erdos, a brilliant number theorist who was known for his open collaboration with others.


Mike's notes page is souptonuts. For open source consulting needs, please send an email to mchirico@gmail.com. All consulting work must include a donation to SourceForge.net.

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