/* cc thisfile.c -lthread */
#define _REENTRANT
#include <stdio.h>
#include <thread.h>
#define NUM_THREADS 6 
               static mutex_t Global_mutex;
               static int     Global_data = 0;
void *change_global_data(void *);     /*  for thr_create()   */
void *schange_global_data(void *);     /*  for thr_create()   */
          main(int argc,char * argv[])  {
               int i=0;
               for (i=0; i< NUM_THREADS; i++)     {
                    thr_create(NULL, 0, change_global_data, NULL, 0, NULL);
               }

              for (i=0; i< NUM_THREADS; i++)     {
                    thr_create(NULL, 0, schange_global_data, NULL, 0, NULL);
               }

               while ((thr_join(NULL, NULL, NULL) == 0));
          }

void * change_global_data(void *null)   {
               int i;
               mutex_lock(&Global_mutex);
               printf("%d is before  \n", i);
               i=Global_data; 
               printf("%d is after \n", i);
               Global_data++;
               sleep(1);
               printf("%d is global data\n",Global_data);
               mutex_unlock(&Global_mutex);
                return NULL;
          }

void * schange_global_data(void *null)   {
               int i;
               mutex_lock(&Global_mutex);
               printf("%d is before  \n", i);
               i=Global_data; 
               printf("%d is after \n", i);
               Global_data--;
               sleep(1);
               printf("%d is global data\n",Global_data);
               mutex_unlock(&Global_mutex);
                return NULL;
          }