/* parallel Monte Carlo area calculation */
/* master program */

#include <stdio.h>
#include <pvm3.h>

#define task 100			/* number of tasks per quadrant */


main()
{
struct pvmhostinfo *hostp;
int bufid, check, dum, htid, nhost, narch, ptid, stid, type;
int back[1], done[5], i, j, q, k, min_t, min_q, result;
char name[20], name2[20], tmp[2];
double area;

ptid = pvm_mytid();			/* get your PVM ID number */

pvm_config( &nhost, &narch, &hostp );	/* configuration of virtual machine */
gethostname(name, 20);
printf("The master process runs on %s \n", name);
printf("I found the following hosts in your virtual machine\n");
for (i = 0; i < nhost; i++)
{ 
   printf("\t%s\n", hostp[i].hi_name);
}

printf("\nStarting slaves\n");

for (i=0; i<4; i++) done[i]=0;		/* reset some counters */
i=0;
j=0;
result=0;

do				
{
   i++;					/* start slaves 1,2,3,4,1,... */
   if(i==5) i=1;			/* until all machines have a */
   strcpy(name, "monteslave");       	/* job running */
   sprintf(tmp, "%i", i);
   strcat(name, tmp);
   check=pvm_spawn(name, 0,PvmTaskHost,hostp[j].hi_name, 1, &stid);
   if (!check) 
   {
      printf("Couldn't start process on %s\n", hostp[j].hi_name);
      nhost--;
   }
   else
   {
      printf("started slave for quadrant %i on %s\n", i, hostp[j].hi_name);
      done[i]++;
   }
   j++;
}while ((j<nhost) && (j<4*task));


for(i=j; i<4*task; i++)			/* wait for slaves to finish to */
{					/* start all additional tasks */
   bufid=pvm_recv(-1, -1);                      /* any machine any message*/
   pvm_bufinfo(bufid, &dum, &type, &stid);	/* where from, which quadrant */
   pvm_upkint(back, 1, 1);			/* the result of the task */
   result+=back[0];
   if (done[type]<task)			/* there are still open tasks in */
   {					/* this quadrant so */
       pvm_initsend(PvmDataDefault);	/* tell slave to continue */
       pvm_send(stid, 1);
       done[type]++;
   }
   else					/* no open tasks in this quadrant */
   {					/* so start a different slave */
      printf("quadrant %i is done\n", type);
      htid=pvm_tidtohost(stid);			/* find host of this slave */
      for (k=0; k<nhost; k++)
      {
         if (htid==hostp[k].hi_tid) strcpy(name2, hostp[k].hi_name);
      }   
      pvm_initsend(PvmDataDefault);		/* tell slave to shut down */
      pvm_send(stid, 0);
      min_t=done[1];				/* find quadrant with most */
      min_q=1;					/* open tasks - this way */
      for (k=2; k<5; k++)			/* the fastest machine */
      {						/* will work on a new */
         if (done[k]<min_t)			/* quadrant or together */
         {   					/* with a slow machine */
            min_t=done[k];			/* after it's done */
            min_q=k;
         }   
      }
      strcpy(name, "monteslave");		/* which slave to start */      
      sprintf(tmp, "%i", min_q);
      strcat(name, tmp);
      pvm_spawn(name, 0,PvmTaskHost, name2, 1, &stid);
      printf("started slave for quadrant %i on %s\n", min_q, name2);
      done[min_q]++;
   }
}

for(i=0; i<nhost; i++)			/* wait for last tasks to end */
{
   bufid=pvm_recv(-1, -1);                      /* any machine any message*/
   pvm_bufinfo(bufid, &dum, &dum, &stid);	/* where from */ 
   pvm_upkint(back, 1, 1);
   result+=back[0];
   pvm_initsend(PvmDataDefault);		/* tell slave to shut down */
   pvm_send(stid, 0);
}
area=result;					/* calculate final result */  
printf("the area is %f\n", area/(task*4*50000));
pvm_exit;
}