// multiple threads generating musical notes
//
// POSIX version
//
#include <stdio.h>
#include <math.h>
#include <pthread.h>
#include <sched.h>
#include <assert.h>
//
// compile flags: -pthread

#define Pthread_create(a,b,c,d)	assert(pthread_create(a,b,c,d) == 0)
 
#define N 2 // number of threads
 
int notes0[] = { 44, 6, 42, 6, 40, 12, -1 };
int notes1[] = { 47, 2, 52, 4, 52, 2, 51, 2, 49, 2, 51, 2, 52, 4, 47, 2, 47, 4, -1 };
 
typedef struct
{
  int wait;	// 0 = play() should wait, 1 = main() should wait, -1 = done
  int *notes;	// key, duration pairs, end with -1
  double value;	// output value
}
Data;
 
Data D[N] = { { 1, notes0, 0 }, { 1, notes1, 0 } };
 
double pi, ratio;
 
void play( int key, int duration, Data *d)
{
  double r, w = (2*pi*440*pow(ratio,key-49))/8000.0;
 
  int n = (duration/10.0)*8000.0;
 
  for( int i = 0; i < n; ++i)
  {
    r = sin(w*i) + 0.5*sin(2*w*i) + 0.25*sin(3*w*i);
    while( d->wait == 0) sched_yield();
    d->value = r;
    d->wait = 0;
  }
}
 
void *f( void *v)
{
  Data *d = v;
 
  for( int i = 0; d->notes[i] >= 0; i += 2) play( d->notes[i], d->notes[i+1], d);
 
  while( d->wait == 0) sched_yield();
 
  d->wait = -1; // done
 
  return 0;
}
 
int main( void)
{
  int done;  double sum;  pthread_t t[N];
 
  pi = 4*atan(1);  ratio = pow(2,1.0/12.0);
 
  for( int i = 0; i < N; ++i) Pthread_create( t+i, 0, f, D+i);
 
  while( 1)
  {
    done = 1; sum = 0;
 
    for( int i = 0; i < N; ++i)
    {
      while( D[i].wait == 1) sched_yield();
 
      if( D[i].wait == 0) { done = 0; sum += D[i].value; D[i].wait = 1; }
    }
 
    if( done) break;
 
    printf( "%g\n", sum);
  }
 
  return 0;
}