fix unwinding symmetric coroutine

example/cpp03/symmetric/unwind.cpp

@@ -0,0 +1,50 @@
+
+//          Copyright Oliver Kowalke 2009.
+// Distributed under the Boost Software License, Version 1.0.
+//    (See accompanying file LICENSE_1_0.txt or copy at
+//          http://www.boost.org/LICENSE_1_0.txt)
+
+#include <cstdlib>
+#include <iostream>
+
+#include <boost/bind.hpp>
+#include <boost/coroutine/all.hpp>
+
+struct X : private boost::noncopyable
+{
+    X() { std::cout << "X()" << std::endl; }
+    ~X() { std::cout << "~X()" << std::endl; }
+};
+
+typedef boost::coroutines::symmetric_coroutine< void >  coro_t;
+
+coro_t::call_type * c1 = 0;
+coro_t::call_type * c2 = 0;
+
+void foo( coro_t::yield_type & yield)
+{
+    X x;
+    std::cout << "foo() entered" << std::endl;
+    yield( * c2);
+    yield( * c2);
+    std::cout << "foo() finished" << std::endl;
+}
+
+void bar( coro_t::yield_type & yield)
+{
+    std::cout << "bar() entered" << std::endl;
+    yield( * c1);
+    std::cout << "bar() finished" << std::endl;
+}
+
+int main( int argc, char * argv[])
+{
+    coro_t::call_type coro1( foo);
+    coro_t::call_type coro2( bar);
+    c1 = & coro1;
+    c2 = & coro2;
+    coro1();
+    std::cout << "Done" << std::endl;
+
+    return EXIT_SUCCESS;
+}