input/BufferedInputStream: new wrapper for moving plugin to thread

src/input/ThreadInputStream.hxx

@@ -0,0 +1,181 @@
+/*
+ * 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.
+ */
+
+#ifndef MPD_THREAD_INPUT_STREAM_HXX
+#define MPD_THREAD_INPUT_STREAM_HXX
+
+#include "check.h"
+#include "InputStream.hxx"
+#include "thread/Thread.hxx"
+#include "thread/Cond.hxx"
+#include "util/Cast.hxx"
+#include "util/Error.hxx"
+
+#include <stdint.h>
+
+template<typename T> class CircularBuffer;
+
+/**
+ * Helper class for moving InputStream implementations with blocking
+ * backend library implementation to a dedicated thread.  Data is
+ * being read into a ring buffer, and that buffer is then consumed by
+ * another thread using the regular #InputStream API.  This class
+ * manages the thread and the buffer.
+ *
+ * This works only for "streams": unknown length, no seeking, no tags.
+ */
+class ThreadInputStream {
+	InputStream base;
+
+	Thread thread;
+
+	/**
+	 * Signalled when the thread shall be woken up: when data from
+	 * the buffer has been consumed and when the stream shall be
+	 * closed.
+	 */
+	Cond wake_cond;
+
+	Error postponed_error;
+
+	const size_t buffer_size;
+	CircularBuffer<uint8_t> *buffer;
+
+	/**
+	 * Shall the stream be closed?
+	 */
+	bool close;
+
+	/**
+	 * Has the end of the stream been seen by the thread?
+	 */
+	bool eof;
+
+public:
+	ThreadInputStream(const InputPlugin &_plugin,
+			  const char *_uri, Mutex &_mutex, Cond &_cond,
+			  size_t _buffer_size)
+		:base(_plugin, _uri, _mutex, _cond),
+		 buffer_size(_buffer_size),
+		 buffer(nullptr),
+		 close(false), eof(false) {}
+
+	virtual ~ThreadInputStream();
+
+	/**
+	 * Initialize the object and start the thread.
+	 *
+	 * @return false on error
+	 */
+	InputStream *Start(Error &error);
+
+protected:
+	void Lock() {
+		base.mutex.lock();
+	}
+
+	void Unlock() {
+		base.mutex.unlock();
+	}
+
+	const char *GetURI() const {
+		assert(thread.IsInside());
+
+		return base.uri.c_str();
+	}
+
+	void SetMimeType(const char *mime) {
+		assert(thread.IsInside());
+
+		base.mime = mime;
+	}
+
+	/* to be implemented by the plugin */
+
+	/**
+	 * Optional initialization after entering the thread.  After
+	 * this returns with success, the InputStream::ready flag is
+	 * set.
+	 *
+	 * The #InputStream is locked.  Unlock/relock it if you do a
+	 * blocking operation.
+	 */
+	virtual bool Open(gcc_unused Error &error) {
+		return true;
+	}
+
+	/**
+	 * Read from the stream.
+	 *
+	 * The #InputStream is not locked.
+	 *
+	 * @return 0 on end-of-file or on error
+	 */
+	virtual size_t Read(void *ptr, size_t size, Error &error) = 0;
+
+	/**
+	 * Optional deinitialization before leaving the thread.
+	 *
+	 * The #InputStream is not locked.
+	 */
+	virtual void Close() {}
+
+	/**
+	 * Called from the client thread to cancel a Read() inside the
+	 * thread.
+	 *
+	 * The #InputStream is not locked.
+	 */
+	virtual void Cancel() {}
+
+private:
+
+#if GCC_CHECK_VERSION(4,6) || defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Winvalid-offsetof"
+#endif
+
+	static constexpr ThreadInputStream *Cast(InputStream *is) {
+		return ContainerCast(is, ThreadInputStream, base);
+	}
+
+#if GCC_CHECK_VERSION(4,6) || defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
+
+	void ThreadFunc();
+	static void ThreadFunc(void *ctx);
+
+	bool Check2(Error &error);
+	bool Available2();
+	size_t Read2(void *ptr, size_t size, Error &error);
+	void Close2();
+	bool IsEOF2();
+
+public:
+	/* InputPlugin callbacks */
+	static bool Check(InputStream *is, Error &error);
+	static bool Available(InputStream *is);
+	static size_t Read(InputStream *is, void *ptr, size_t size,
+			   Error &error);
+	static void Close(InputStream *is);
+	static bool IsEOF(InputStream *is);
+};
+
+#endif