persistable sclass BoolVar {
  bool a; // you can access this directly if you use one thread
  
  *() {}
  *(bool *a) {}
  
  public synchronized void set(bool v default true) {
    if (v != a) {
      a = v;
      notifyAll();
    }
  }
  
  public synchronized bool get() { ret a; }
  //public synchronized bool has() { true; }
  public void clear aka unset() { set(false); }
  
  bool waitUntilTrue () { ret waitForValue(true); }
  bool waitUntilFalse() { ret waitForValue(false); }
  
  bool waitUntilTrue (double timeoutSeconds) { ret waitForValue(timeoutSeconds, true); }
  bool waitUntilFalse(double timeoutSeconds) { ret waitForValue(timeoutSeconds, false); }
  
  synchronized bool waitForValue(bool wantedValue) ctex {
    while (a != wantedValue)
      wait();
    ret a;
  }
  
  synchronized bool waitForValue(double timeoutSeconds, bool wantedValue) ctex {
    if (timeoutSeconds == infinity())
      ret waitForValue(wantedValue);
      
    long destTime = sysNowPlusSeconds_noPing(timeoutSeconds), remainingTime;
    while (a != wantedValue
      && (remainingTime = destTime-sysNow_noPing()) > 0)
      wait(remainingTime);

    ret a;
  }
  
  public synchronized bool getAndSet(bool b) {
    var value = a;
    set(b);
    ret value;
  }
  
  public synchronized bool waitUntilTrueAndClear() {
    if (!waitUntilTrue()) false;
    set(false);
    true;
  }
  
  public synchronized bool waitUntilTrueAndClear(double timeoutSeconds) {
    if (!waitUntilTrue(timeoutSeconds)) false;
    set(false);
    true;
  }
  
  O mutex() { this; }
}