New double buffer class in Raul (used for realtime-safe thread-safe writes to variables

used in the realtime audio thead).
Manipulation of edge labels in Machina (left click and right click).


git-svn-id: http://svn.drobilla.net/lad/raul@323 a436a847-0d15-0410-975c-d299462d15a1

2 files changed, 97 insertions, 0 deletions

diff --git a/raul/DoubleBuffer.h b/raul/DoubleBuffer.h
new file mode 100644
index 0000000..75f70e5
--- /dev/null
+++ b/raul/DoubleBuffer.h
@@ -0,0 +1,96 @@
+/* This file is part of Raul.
+ * Copyright (C) 2007 Dave Robillard <http://drobilla.net>
+ * 
+ * Raul 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.
+ * 
+ * Raul 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 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 St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef RAUL_DOUBLE_BUFFER_H
+#define RAUL_DOUBLE_BUFFER_H
+
+#include <raul/AtomicInt.h>
+#include <raul/AtomicPtr.h>
+
+namespace Raul {
+
+/** Double buffer.
+ *
+ * Can be thought of as a wrapper class to make a non-atomic type atomically
+ * settable (with no locking).
+ *
+ * Read/Write realtime safe, many writers safe - but set calls may fail.
+ *
+ * Space:  2*sizeof(T) + sizeof(int) + sizeof(void*)
+ */
+template<typename T>
+class DoubleBuffer {
+public:
+	
+	inline DoubleBuffer(T val)
+		: _state(READ_WRITE)
+	{
+		_vals[0] = val;
+		_read_val = &_vals[0];
+	}
+
+	inline T& get()
+	{
+		return *_read_val.get();
+	}
+
+	inline bool set(T new_val)
+	{
+		if (_state.compare_and_exchange(READ_WRITE, READ_LOCK)) {
+
+			// locked _vals[1] for write
+			_vals[1] = new_val;
+			_read_val = &_vals[1];
+			_state = WRITE_READ;
+			return true;
+
+			// concurrent calls here are fine.  good, actually - caught
+			// the WRITE_READ state immediately after it was set above
+
+		} else if (_state.compare_and_exchange(WRITE_READ, LOCK_READ)) {
+
+			// locked _vals[0] for write
+			_vals[0] = new_val;
+			_read_val = &_vals[0];
+			_state = READ_WRITE;
+			return true;
+
+		} else {
+
+			return false;
+
+		}
+	}
+
+private:
+	enum States {
+		// vals[0] state _ vals[1] state
+		READ_WRITE = 0,
+		READ_LOCK,
+		WRITE_READ,
+		LOCK_READ
+	};
+
+	AtomicInt    _state;
+	AtomicPtr<T> _read_val;
+	T            _vals[2];
+};
+
+
+} // namespace Raul
+
+#endif // RAUL_DOUBLE_BUFFER_H
diff --git a/raul/Makefile.am b/raul/Makefile.am
index bd233a9..359e46f 100644
--- a/raul/Makefile.am
+++ b/raul/Makefile.am
@@ -7,6 +7,7 @@ raulinclude_HEADERS = \
 	AtomRaptor.h \
 	AtomicInt.h \
 	AtomicPtr.h \
+	DoubleBuffer.h \
 	Condition.h \
 	Deletable.h \
 	JackDriver.h \