Introduce BAdapterIO

* This class is provided as a safe multithreaded communication channel
between a BMediaIO-like interface and a Read/Write backend.
* Includes internal buffering and can be used to provide multithreaded
edit of the data.
* Current limitations include missing BOutputAdapter and
correct timeout handling.
* Future plans provide a BRemoteAdapterIO that using ports
and areas allow to easily send big data between processes.

headers/private/media/AdapterIO.h

@@ -0,0 +1,89 @@
+/*
+ * Copyright 2016 Haiku, Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _ADAPTER_IO_H
+#define _ADAPTER_IO_H
+
+
+#include <MediaIO.h>
+#include <OS.h>
+#include <RWLocker.h>
+#include <SupportDefs.h>
+
+
+class BAdapterIO;
+
+
+class BInputAdapter {
+public:
+	virtual	ssize_t			Write(const void* buffer, size_t size);
+
+private:
+	friend class BAdapterIO;
+
+							BInputAdapter(BAdapterIO* io);
+	virtual					~BInputAdapter();
+
+			BAdapterIO*		fIO;
+
+	virtual	void			_ReservedInputAdapter1();
+	virtual void			_ReservedInputAdapter2();
+
+			uint32			_reserved[2];
+};
+
+
+class BAdapterIO : public BMediaIO {
+public:
+							BAdapterIO(int32 flags,
+								bigtime_t timeout = B_INFINITE_TIMEOUT);
+	virtual					~BAdapterIO();
+
+	virtual void			GetFlags(int32* flags) const;
+
+	virtual	ssize_t			ReadAt(off_t position, void* buffer,
+								size_t size);
+	virtual	ssize_t			WriteAt(off_t position,
+								const void* buffer, size_t size);
+
+	virtual	off_t			Seek(off_t position, uint32 seekMode);
+	virtual off_t			Position() const;
+
+	virtual	status_t		SetSize(off_t size);
+	virtual	status_t		GetSize(off_t* size) const;
+
+			BInputAdapter*	BuildInputAdapter();
+
+protected:
+	friend class BInputAdapter;
+
+			void			SetBuffer(BPositionIO* io);
+
+			ssize_t			BackWrite(const void* buffer, size_t size);
+
+private:
+			void			_WaitForData(size_t size);
+
+			int32			fFlags;
+			bigtime_t		fTimeout;
+
+			off_t			fBackPosition;
+	mutable RWLocker		fLock;
+			BPositionIO*	fBuffer;
+
+			BInputAdapter*	fInputAdapter;
+
+							BAdapterIO(const BAdapterIO&);
+			BAdapterIO&		operator=(const BAdapterIO&);
+
+	virtual	void			_ReservedAdapterIO1();
+	virtual void			_ReservedAdapterIO2();
+	virtual void			_ReservedAdapterIO3();
+	virtual void			_ReservedAdapterIO4();
+	virtual void			_ReservedAdapterIO5();
+
+			uint32			_reserved[5];
+};
+
+#endif	// _ADAPTER_IO_H