Signals lib - causes mysterious multiple destructor calls

From: Chuck Messenger (yg-boost-users_at_[hidden])
Date: 2003-05-16 08:58:40

Testing out the Boost signals lib, I wrote:

-----------
#include <boost/signal.hpp>
#include <iostream>

using namespace std;
using namespace boost;

struct X {
     void operator()(int val) { cout << "X <- " << val << endl; }
     X() { cout << "X constructor\n"; }
     ~X() { cout << "X destructor\n"; }
};

int main() {
     {
         cout << "   phase 1\n";
         signal<void (int)> sig;
         cout << "   phase 2\n";
         X x;
         cout << "   phase 3\n";
         sig.connect(x);
         cout << "   phase 4\n";
     }
     cout << "   phase 5\n";

     return 0;
}
-------------------

The following output is generated (gcc3.2.2 on Mandrake 9.1):

------------------------
    phase 1
    phase 2
X constructor
    phase 3
X destructor
X destructor
X destructor
X destructor
X destructor
X destructor
X destructor
X destructor
    phase 4
X destructor
X destructor
    phase 5
------------------------

Why the multiple calls to X's destructor?  I'd have expected just one. 
It looks like the signals lib is misbehaving.

Can anyone offer an explanation?

     - Chuck