1 files changed, 97 insertions, 0 deletions
diff --git a/src/db/DatabaseLock.hxx b/src/db/DatabaseLock.hxx
new file mode 100644
index 000000000..9d0b0c152
--- /dev/null
+++ b/src/db/DatabaseLock.hxx
@@ -0,0 +1,97 @@
+/*
+ * 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.
+ */
+
+/** \file
+ *
+ * Support for locking data structures from the database, for safe
+ * multi-threading.
+ */
+
+#ifndef MPD_DB_LOCK_HXX
+#define MPD_DB_LOCK_HXX
+
+#include "check.h"
+#include "thread/Mutex.hxx"
+#include "Compiler.h"
+
+#include <assert.h>
+
+extern Mutex db_mutex;
+
+#ifndef NDEBUG
+
+#include "thread/Id.hxx"
+
+extern ThreadId db_mutex_holder;
+
+/**
+ * Does the current thread hold the database lock?
+ */
+gcc_pure
+static inline bool
+holding_db_lock(void)
+{
+	return db_mutex_holder.IsInside();
+}
+
+#endif
+
+/**
+ * Obtain the global database lock.  This is needed before
+ * dereferencing a #song or #directory.  It is not recursive.
+ */
+static inline void
+db_lock(void)
+{
+	assert(!holding_db_lock());
+
+	db_mutex.lock();
+
+	assert(db_mutex_holder.IsNull());
+#ifndef NDEBUG
+	db_mutex_holder = ThreadId::GetCurrent();
+#endif
+}
+
+/**
+ * Release the global database lock.
+ */
+static inline void
+db_unlock(void)
+{
+	assert(holding_db_lock());
+#ifndef NDEBUG
+	db_mutex_holder = ThreadId::Null();
+#endif
+
+	db_mutex.unlock();
+}
+
+class ScopeDatabaseLock {
+public:
+	ScopeDatabaseLock() {
+		db_lock();
+	}
+
+	~ScopeDatabaseLock() {
+		db_unlock();
+	}
+};
+
+#endif