source: CIVL/examples/pthread/cprover/07_rand_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; } }

int m = 0;

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

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

volatile int seed; 

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

        __VERIFIER_atomic_acquire();
        read = seed;

        do
        {
                nexts = __VERIFIER_nondet_int();
        }
        while(nexts == read || nexts == 0);

        assert(nexts != read); 
        seed = nexts;
        __VERIFIER_atomic_release();
        nextInt_return = nexts % n;
        //assume(nexts < n + 1);
        //nextInt_return = nexts;

        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); }
}