public class A {

private int count = 0;

public static final int THREHOLD = 100;

public synchronized boolean getTicket() {
if (count > THREHOLD) {
count++;
return true;
} else {
return false;
}
}

public synchronized boolean release() {
count--;
}

public void run() {
if (getTicket()) {
...
release();
}
}
}