genode/ports/src/noux/pipe_io_channel.h

/*
 * \brief  I/O channels for pipe input/output
 * \author Norman Feske
 * \date   2012-03-19
 */

/*
 * Copyright (C) 2012 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU General Public License version 2.
 */

#ifndef _NOUX__PIPE_IO_CHANNEL_H_
#define _NOUX__PIPE_IO_CHANNEL_H_

/* Noux includes */
#include <io_channel.h>

namespace Noux {

	class Pipe : public Reference_counter
	{
		private:

			Lock mutable _lock;

			enum { BUFFER_SIZE = 4096 };
			char _buffer[BUFFER_SIZE];

			unsigned _read_offset;
			unsigned _write_offset;

			Signal_context_capability _read_ready_sigh;
			Signal_context_capability _write_ready_sigh;

			bool _writer_is_gone;

			/**
			 * Return space available in the buffer for writing, in bytes
			 */
			size_t _avail_buffer_space() const
			{
				if (_read_offset < _write_offset)
					return (BUFFER_SIZE - _write_offset) + _read_offset - 1;

				if (_read_offset > _write_offset)
					return _read_offset - _write_offset - 1;

				/* _read_offset == _write_offset */
				return BUFFER_SIZE - 1;
			}

			bool _any_space_avail_for_writing() const
			{
				return _avail_buffer_space() > 0;;
			}

			void _wake_up_reader()
			{
				if (_read_ready_sigh.valid())
					Signal_transmitter(_read_ready_sigh).submit();
			}

			void _wake_up_writer()
			{
				if (_write_ready_sigh.valid())
					Signal_transmitter(_write_ready_sigh).submit();
			}

		public:

			Pipe()
			: _read_offset(0), _write_offset(0), _writer_is_gone(false) { }

			~Pipe()
			{
				Lock::Guard guard(_lock);
			}

			void writer_close()
			{
				Lock::Guard guard(_lock);

				_writer_is_gone = true;
				_write_ready_sigh = Signal_context_capability();
				_wake_up_reader();
			}

			void reader_close()
			{
				Lock::Guard guard(_lock);
				_read_ready_sigh = Signal_context_capability();
			}

			bool writer_is_gone() const
			{
				Lock::Guard guard(_lock);
				return _writer_is_gone;
			}

			bool any_space_avail_for_writing() const
			{
				Lock::Guard guard(_lock);
				return _any_space_avail_for_writing();
			}

			bool data_avail_for_reading() const
			{
				Lock::Guard guard(_lock);

				return _read_offset != _write_offset;
			}

			size_t read(char *dst, size_t dst_len)
			{
				Lock::Guard guard(_lock);

				if (_read_offset < _write_offset) {

					size_t len = min(dst_len, _write_offset - _read_offset);
					memcpy(dst, &_buffer[_read_offset], len);

					_read_offset += len;
					_wake_up_writer();

					return len;
				}

				if (_read_offset > _write_offset) {

					size_t const upper_len = min(dst_len, BUFFER_SIZE - _read_offset);
					memcpy(dst, &_buffer[_read_offset], upper_len);

					size_t const lower_len = min(dst_len - upper_len, _write_offset);
					memcpy(dst + upper_len, &_buffer[0], lower_len);

					_read_offset = lower_len;
					_wake_up_writer();

					return upper_len + lower_len;
				}

				/* _read_offset == _write_offset */
				return 0;
			}

			/**
			 * Write to pipe buffer
			 *
			 * \return number of written bytes (may be less than 'len')
			 */
			size_t write(char *src, size_t len)
			{
				Lock::Guard guard(_lock);

				/* trim write request to the available buffer space */
				size_t const trimmed_len = min(len, _avail_buffer_space());

				/*
				 * Remember pipe state prior writing to see whether a reader
				 * must be unblocked after writing.
				 */
				bool const pipe_was_empty = (_read_offset == _write_offset);

				/* write data up to the upper boundary of the pipe buffer */
				size_t const upper_len = min(BUFFER_SIZE - _write_offset, trimmed_len);
				memcpy(&_buffer[_write_offset], src, upper_len);

				_write_offset += upper_len;

				/*
				 * Determine number of remaining bytes beyond the buffer boundary.
				 * The buffer wraps. So this data will end up in the lower part
				 * of the pipe buffer.
				 */
				size_t const lower_len = trimmed_len - upper_len;

				if (lower_len > 0) {

					/* pipe buffer wrap-around, write remaining data to the lower part */
					memcpy(&_buffer[0], src + upper_len, lower_len);
					_write_offset = lower_len;
				}

				/*
				 * Wake up reader who may block for incoming data.
				 */
				if (pipe_was_empty || !_any_space_avail_for_writing())
					_wake_up_reader();

				/* return number of written bytes */
				return trimmed_len;
			}

			void register_write_ready_sigh(Signal_context_capability sigh)
			{
				Lock::Guard guard(_lock);
				_write_ready_sigh = sigh;
			}

			void register_read_ready_sigh(Signal_context_capability sigh)
			{
				Lock::Guard guard(_lock);
				_read_ready_sigh = sigh;
			}
	};


	class Pipe_sink_io_channel : public Io_channel, public Signal_dispatcher_base
	{
		private:

			Shared_pointer<Pipe> _pipe;
			Signal_receiver     &_sig_rec;

		public:

			Pipe_sink_io_channel(Shared_pointer<Pipe> pipe,
			                     Signal_receiver &sig_rec)
			: _pipe(pipe), _sig_rec(sig_rec)
			{
				pipe->register_write_ready_sigh(_sig_rec.manage(this));
			}

			~Pipe_sink_io_channel()
			{
				_sig_rec.dissolve(this);
				_pipe->writer_close();
			}

			bool check_unblock(bool rd, bool wr, bool ex) const
			{
				return wr && _pipe->any_space_avail_for_writing();
			}

			bool write(Sysio *sysio, size_t &count)
			{
				/*
				 * If the write operation is larger than the space available in
				 * the pipe buffer, the write function is successively called
				 * for different portions of original write request. The
				 * current read pointer of the request is tracked via the
				 * 'count' in/out argument. If completed, 'count' equals
				 * 'write_in.count'.
				 */

				/* dimension the pipe write operation to the not yet written data */
				size_t curr_count = _pipe->write(sysio->write_in.chunk + count,
				                                 sysio->write_in.count - count);
				count += curr_count;
				return true;
			}

			bool fstat(Sysio *sysio)
			{
				sysio->fstat_out.st.mode = Sysio::STAT_MODE_CHARDEV;
				return true;
			}

			/**************************************
			 ** Signal_dispatcher_base interface **
			 **************************************/

			/**
			 * Called by Noux main loop on the occurrence of new STDIN input
			 */
			void dispatch(unsigned)
			{
				Io_channel::invoke_all_notifiers();
			}
	};


	class Pipe_source_io_channel : public Io_channel, public Signal_dispatcher_base
	{
		private:

			Shared_pointer<Pipe> _pipe;
			Signal_receiver     &_sig_rec;

		public:

			Pipe_source_io_channel(Shared_pointer<Pipe> pipe, Signal_receiver &sig_rec)
			: _pipe(pipe), _sig_rec(sig_rec)
			{
				_pipe->register_read_ready_sigh(sig_rec.manage(this));
			}

			~Pipe_source_io_channel()
			{
				_sig_rec.dissolve(this);
				_pipe->reader_close();
			}

			bool check_unblock(bool rd, bool wr, bool ex) const
			{
				/* unblock if the writer has already closed its pipe end */
				if (_pipe->writer_is_gone())
					return true;

				return (rd && _pipe->data_avail_for_reading());
			}

			bool read(Sysio *sysio)
			{
				size_t const max_count =
					min(sysio->read_in.count,
					    sizeof(sysio->read_out.chunk));

				sysio->read_out.count =
					_pipe->read(sysio->read_out.chunk, max_count);

				return true;
			}

			bool fstat(Sysio *sysio)
			{
				sysio->fstat_out.st.mode = Sysio::STAT_MODE_CHARDEV;
				return true;
			}

			/**************************************
			 ** Signal_dispatcher_base interface **
			 **************************************/

			/**
			 * Called by Noux main loop on the occurrence of new STDIN input
			 */
			void dispatch(unsigned)
			{
				Io_channel::invoke_all_notifiers();
			}
	};
}

#endif /* _NOUX__PIPE_IO_CHANNEL_H_ */