我们首先开发一个BusyFlag的类，类似于C++中的Simaphore。
public class BusyFlag {
protected Thread busyflag = null;
protected int busycount = 0;
public synchronized void getBusyFlag() {
while (tryGetBusyFlag() == false) {
try {
wait();
} catch (Exception e) {}
}
}
private synchronized boolean tryGetBusyFlag() {
if (busyflag == null) {
busyflag = Thread.currentThread();
busycount = 1;
return true;
}
if (busyflag == Thread.currentThread()) {
busycount++;
return true;
}
return false;
}
public synchronized void freeBusyFlag() {
if(getOwner()== Thread.currentThread()) {
busycount--;
if(busycount==0) {
busyflag = null;
notify();
}
}
}
public synchronized Thread getOwner() {
return busyflag;
}
}
