source: CIVL/examples/pthread/cprover/08_rand_cas_true.c@ 1aaefd4

//http://www.ibm.com/developerworks/java/library/j-jtp11234/
//Listing 5. Implementing a thread-safe PRNG with synchronization and atomic variables

#include <pthread.h>

#define assume(e) __VERIFIER_assume(e)
#define assert(e) { if(!(e)) { ERROR: goto ERROR; (void)0; } }

inline int calculateNext(int s2){ 
        int calculateNext_return;
        do
        {
                calculateNext_return = __VERIFIER_nondet_int();
        }
        while(calculateNext_return == s2 || calculateNext_return == 0);

        return calculateNext_return;
}

volatile int seed, m=0;

void __VERIFIER_atomic_acquire()
{
        assume(m==0);
        m = 1;
}

void __VERIFIER_atomic_release()
{
        assume(m==1);
        m = 0;
}

void __VERIFIER_atomic_CAS(
  volatile int *v,
  int e,
  int u,
  int *r)
{
        if(*v == e)
        {
                *v = u, *r = 1;
        }
        else
        {
                *r = 0;
        }
}

inline int PseudoRandomUsingAtomic_nextInt(int n)
{
        int read, nexts, casret, nextInt_return;

        while(1) {
                read = seed;
                nexts = calculateNext(read);
                assert(nexts != read); 
                __VERIFIER_atomic_CAS(&seed,read,nexts,&casret);

                if(casret == 1){
                        nextInt_return = nexts % n;
                        //assume(nexts < n);
                        //nextInt_return = nexts;
                        break;
                }
        }

        return nextInt_return;
}

inline void PseudoRandomUsingAtomic_monitor()
{
        while(1)
        {
                assert(seed != 0);
        }
}

inline void PseudoRandomUsingAtomic_constructor(int init)
{
        seed = init;
}

inline void PseudoRandomUsingAtomic__threadmain()
{ 
        int myrand;

        myrand = PseudoRandomUsingAtomic_nextInt(10);
        assert(myrand <= 10);
}

#define STATE_UNINITIALIZED     0
#define STATE_INITIALIZED       1

volatile int state = STATE_UNINITIALIZED;
void* thr1(void* arg)
{
        __VERIFIER_atomic_acquire();
        switch(state)
        {
        case (STATE_UNINITIALIZED): 
                PseudoRandomUsingAtomic_constructor(1);
                state = STATE_INITIALIZED;
                __VERIFIER_atomic_release();
                
                PseudoRandomUsingAtomic_monitor(); //never returns
                break;
        case (STATE_INITIALIZED): 
                __VERIFIER_atomic_release();
                
                PseudoRandomUsingAtomic__threadmain();
                break;
        }

  return 0;
}

int main()
{
  pthread_t t;

        while(1) { pthread_create(&t, 0, thr1, 0); }
}