event: add function BlockingCall()

Replaces io_thread_call().  This approach is more generic and easier
to use due to std::function.

src/event/Call.cxx

@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2003-2013 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 "Call.hxx"
+#include "Loop.hxx"
+#include "DeferredMonitor.hxx"
+#include "thread/Mutex.hxx"
+#include "thread/Cond.hxx"
+#include "gcc.h"
+
+#include <assert.h>
+
+class BlockingCallMonitor final : DeferredMonitor {
+	const std::function<void()> f;
+
+	Mutex mutex;
+	Cond cond;
+
+	bool done;
+
+public:
+	BlockingCallMonitor(EventLoop &_loop, std::function<void()> &&_f)
+		:DeferredMonitor(_loop), f(std::move(_f)), done(false) {}
+
+	void Run() {
+		assert(!done);
+
+		Schedule();
+
+		mutex.lock();
+		while (!done)
+			cond.wait(mutex);
+		mutex.unlock();
+	}
+
+private:
+	virtual void RunDeferred() override {
+		f();
+	}
+};
+
+void
+BlockingCall(EventLoop &loop, std::function<void()> &&f)
+{
+	if (loop.IsInside()) {
+		/* we're already inside the loop - we can simply call
+		   the function */
+		f();
+	} else {
+		/* outside the EventLoop's thread - defer execution to
+		   the EventLoop, wait for completion */
+		BlockingCallMonitor m(loop, std::move(f));
+		m.Run();
+	}
+}

src/event/Call.hxx

@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2003-2013 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.
+ */
+
+#ifndef MPD_EVENT_CALL_HXX
+#define MPD_EVENT_CALL_HXX
+
+#include "check.h"
+
+#include <functional>
+
+class EventLoop;
+
+/**
+ * Call the given function in the context of the #EventLoop, and wait
+ * for it to finish.
+ */
+void
+BlockingCall(EventLoop &loop, std::function<void()> &&f);
+
+#endif /* MAIN_NOTIFY_H */