source: CIVL/examples/concurrency/barrier2.cvl

/* Basic flag barrier.  Same algorithm as barrier.cvl, but
 * packaged to be re-used in other code.
 * Commandline execution:
 *              civl verify -inputB=4 barrier2.cvl
 */
#include <civlc.cvh>

$input int B = 4; // upper bound on number of threads
$input int N;     // number of threads
$assume(1<=N && N<=B);

struct _CIVL_Barrier {
  int numProcs;
  int *in_barrier;
  int num_in_barrier;
  int lock;
};

typedef struct _CIVL_Barrier CIVL_Barrier;

void CIVL_Barrier_init(int numProcs, CIVL_Barrier *barrier, int *array) {  
  barrier->numProcs = numProcs;
  barrier->num_in_barrier = 0;
  barrier->lock = 0;
  barrier->in_barrier = array;
  $for(int i: 0 .. numProcs-1)
    barrier->in_barrier[i] = 0;
}

void CIVL_barrier(CIVL_Barrier *barrier, int tid) {
  $atomic {
    $when (barrier->lock==0) barrier->lock = 1;
    barrier->in_barrier[tid] = 1;
    barrier->num_in_barrier++;
    if (barrier->num_in_barrier == barrier->numProcs) {
      for (int i=0; i<barrier->numProcs; i++)
        barrier->in_barrier[i] = 0;
      barrier->num_in_barrier = 0;
    }
    barrier->lock = 0;
    $yield();
    $when (barrier->in_barrier[tid] == 0);
  }
}


void main() {
  int counter = 0;
  CIVL_Barrier b;
  int barrier_array[N];
  
  void run(int tid) {
    while ($true) {
      $assert(counter == 0);
      CIVL_barrier(&b, tid);
      counter++;
      CIVL_barrier(&b, tid);
      $assert(counter == N);
      CIVL_barrier(&b, tid);
      counter--;
      CIVL_barrier(&b, tid);
    }
  }
  
  CIVL_Barrier_init(N, &b, barrier_array);
  $parfor(int i: 0 .. N-1)
    run(i);  
}