upnp: initialize the client handle only once

Eliminate class LibUPnP and move the code to ClientInit.cxx.  Its
initialization function can be called multiple times, but
UpnpRegisterClient() is called at most once.

src/lib/upnp/ClientInit.cxx

@@ -0,0 +1,93 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "ClientInit.hxx"
+#include "Init.hxx"
+#include "Callback.hxx"
+#include "Domain.hxx"
+#include "thread/Mutex.hxx"
+#include "util/Error.hxx"
+
+#include <upnp/upnptools.h>
+
+static Mutex upnp_client_init_mutex;
+static unsigned upnp_client_ref;
+static UpnpClient_Handle upnp_client_handle;
+
+static int
+UpnpClientCallback(Upnp_EventType et, void *evp, void *cookie)
+{
+	if (cookie == nullptr)
+		/* this is the cookie passed to UpnpRegisterClient();
+		   but can this ever happen?  Will libupnp ever invoke
+		   the registered callback without that cookie? */
+		return UPNP_E_SUCCESS;
+
+	UpnpCallback &callback = UpnpCallback::FromUpnpCookie(cookie);
+	return callback.Invoke(et, evp);
+}
+
+static bool
+DoInit(Error &error)
+{
+	auto code = UpnpRegisterClient(UpnpClientCallback, nullptr,
+				       &upnp_client_handle);
+	if (code != UPNP_E_SUCCESS) {
+		error.Format(upnp_domain, code,
+			     "UpnpRegisterClient() failed: %s",
+			     UpnpGetErrorMessage(code));
+		return false;
+	}
+
+	return true;
+}
+
+bool
+UpnpClientGlobalInit(UpnpClient_Handle &handle, Error &error)
+{
+	if (!UpnpGlobalInit(error))
+		return false;
+
+	upnp_client_init_mutex.lock();
+	bool success = upnp_client_ref > 0 || DoInit(error);
+	upnp_client_init_mutex.unlock();
+
+	if (success) {
+		++upnp_client_ref;
+		handle = upnp_client_handle;
+	} else
+		UpnpGlobalFinish();
+
+	return success;
+}
+
+void
+UpnpClientGlobalFinish()
+{
+	upnp_client_init_mutex.lock();
+
+	assert(upnp_client_ref > 0);
+	if (--upnp_client_ref == 0)
+		UpnpUnRegisterClient(upnp_client_handle);
+
+	upnp_client_init_mutex.unlock();
+
+	UpnpGlobalFinish();
+}