ICE Cond cannot wait after signal

hi, master, I have a small question for ICE Cond. The sample code as below:
I signal a cond variable twice in MyThread and expect I can wait this cond twice in main() function.
But seems the sample code does not run as my experience. Program blocked in second cond.wait(). Could you please give any suggestion about, Is this the right behavior? Thanks very much.

#include <iostream>
#include <IceUtil/Thread.h>
#include <IceUtil/Cond.h>

using namespace std;
using namespace IceUtil;

Mutex mutex;
Cond cond;

class MyThread : public Thread
{
public:
virtual void run()
{
Mutex::Lock lock(mutex);
cout << "In function " << __FUNCTION__ << " singled with tid " <<
this->getThreadControl().id() << endl;
cond.signal();
cond.signal();
}
};

int main()
{
ThreadPtr thread = new MyThread();
thread->start();

// wait for thread execute
{
Mutex::Lock lock(mutex);
cond.wait(lock);
}
cout << "Cond wait in function " << __FUNCTION__ << endl;

Sleep(1000);

{
// wait twice
Mutex::Lock lock(mutex);
cond.wait(lock);
}

cout << "Cond wait in function " << __FUNCTION__ << endl;

thread->getThreadControl().join();
return 0;
}