#include "stdinc.h"
#include "uth.h"

//
// Purpose:	2 threads independently compute fibonacci numbers but yield
//		to each other after every other iteration (i.e., no preemption)
// Usage:	mileA
// Notes:	none
// Functions:  uth_init, uth_create, uth_yield, uth_exit
// Features:  no high-priority threads
// History:
// o 3 Apr 2007	kenw: creation
//

typedef void (func_t)(void);	// 0-arg function

struct th_arg {
  int	id;
  int	n;
};
typedef struct th_arg th_arg_t;

// --| constants |--
//XXX const int	nworkers = 1;	// # fibFiber
const int	nworkers = 2;	// # fibFiber
const int	TickSz = 0;	// tick size (msec); 0 ==> no clock

// --| globals |--
int	debug = 0;
uth_tid_t worker[nworkers];
int	done[nworkers];		// done[i] = 1 when thrd i is done
int	result[nworkers];	// result[i] = fib from thrd i

// --| fib thread |-- 
//	compute fibonacci number
//	fib(5)  = fib(4) + fib(3)
//		= fib (3) + fib(2) + fib(2) + fib(1)
//		= fib (2) + fib(1) + fib(2) + fib(2) + fib(1)
//		= fib (1) + fib(1) + fib(1) + fib(1) + fib(1) + 3 fib(0)
//		= 5
void
fibFiber( void *myarg ) {
  int	whoami = ((th_arg_t *)myarg)->id;
  int	n = ((th_arg_t *)myarg)->n;
  int	ncall = 0;
  int	a, b, tmp;

printf( "+ BEGIN fibFiber %d, n = %d\n", whoami, n );

  if ( n == 0)	b = 0;
  else {
    a = 0;	b = 1;
    for (int i=1; i<n; i++) {
      tmp = a + b;
      a = b;
      b = tmp;
printf( ">>> fibFiber %d:  ncall = %d, i = %d, a = %d, b = %d\n",
					whoami, ncall, i, a, b );
      if ( (++ncall)%2 == 1 ) {
printf( "+++ fibFiber %d yielding:  ncall = %d, i = %d, a = %d, b = %d\n",
      					whoami, ncall, i, a, b );
        uth_yield();
      }
    }
  }

printf( "+ END fibFiber %d with fib(%d) = %d\n", whoami, n, b );
  done[whoami] = 1;
  result[whoami] = b;
  uth_exit( b );
}

// --| root of all evil |--
int
main(void) {
  th_arg_t	fibArg[nworkers];
  int		ndone = 0;
  int		debug;

  setlinebuf(stdout);
  uth_init( nworkers+1, TickSz, debug = 1 );

  for (int i=0; i<nworkers; i++)	done[i] = 0;

  for (int i=0; i<nworkers; i++) {	// create fib fibers
    fibArg[i].id = i;
    fibArg[i].n = 5;
    Uth_create( &worker[i], LO_PRI, (func_t *)&fibFiber, &fibArg[i] );
  }

  ndone = 0;
  for (int i=0; i<nworkers; i++) {	// wait for fibers
    while ( ! done[i] ) {
      uth_yield( );
    }
    ++ndone;
    printf( "+++ Fiber %d returned %d\n", i, result[i] );
  }

  printf( "+++ DONE:  Parent fiber\n" );
}