#include <iostream>
#include <semaphore.h>
using namespace std;
 
int main() {
	sem_t my_sem;
	int val,ec; 
	ec=sem_init(&my_sem, 0, 1);
	if (ec) 
	   cout<<"Error "<<ec<<endl; 
	else {
	  sem_getvalue(&my_sem, &val);
	  cout<<val<<endl; 
	  sem_post(&my_sem); 
	  sem_getvalue(&my_sem, &val);
	  cout<<val<<"   !!!"<<endl; 
	  sem_wait(&my_sem); 
	  sem_getvalue(&my_sem, &val);
	  cout<<val<<endl; 
	  sem_wait(&my_sem); 
	  sem_getvalue(&my_sem, &val);
	  cout<<val<<endl; 
	  sem_trywait(&my_sem);   // ok,  here we are in a single thread, so it's same thread
	  if (ec) {
	    sem_getvalue(&my_sem, &val);
	    cout<<val<<endl;
	  }
	  else cout << "Couldn't acquire"<<endl; 
	}
	return 0;
}

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