poco/Foundation/include/Poco/AsyncIOChannel.h

//
// AsyncIOChannel.h
//
// $Id: //poco/svn/Foundation/include/Poco/AsyncIOChannel.h#2 $
//
// Library: Foundation
// Package: AsyncIO
// Module:  AsyncIOChannel
//
// Definition of the AsyncIOChannel class.
//
// Copyright (c) 2007, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
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// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef Foundation_AsyncIOChannel_INCLUDED
#define Foundation_AsyncIOChannel_INCLUDED


#include "Poco/Foundation.h"
#include "Poco/ActiveDispatcher.h"
#include "Poco/ActiveMethod.h"
#include "Poco/AsyncIOCommand.h"


namespace Poco {


class Foundation_API AsyncIOChannel: public ActiveDispatcher
	/// AsyncIOChannel supports asynchronous I/O operations on
	/// streams or other input/output facilities.
	///
	/// This implementation of asynchronous I/O is based on
	/// blocking I/O operations that are executed in a separate thread.
	/// Some operating systems may provide special asynchronous
	/// I/O operations at the operating system level. However, these
	/// are not used by the current implementation.
	///
	/// I/O operations (in the form of AsyncIOCommand subclass instances)
	/// are queued for execution on an AsyncIOChannel. The AsyncIOChannel's
	/// I/O thread executes all queued commands in FIFO order.
	///
	/// Since AsyncIOChannel is based on ActiveDispatcher, the I/O thread is
	/// taken from the default thread pool. It should be ensured that the
	/// capacity of the default thread pool is sufficient before using
	/// asynchronous I/O. For every AsyncIOChannel instance, one thread
	/// from the default thread pool is needed.
	///
	/// Subclasses of AsyncIOChannel implement asynchronous input/output
	/// for streams and sockets.
	///
	/// The enqueue() active member function is used to enqueue AsyncIOCommand
	/// instances for execution.
	///
	/// The cancel() member function (inherited from ActiveDispatcher) can be
	/// used to cancel all pending requests.
	///
	/// Both the AsyncIOCommand class, and the AsyncIOChannel class offer events
	/// that notify an interested party about the successful or unsuccessful
	/// completion of a command.
	///
	/// There are also two ways to wait for the completion of a command and
	/// obtain its result. The first one is by using the return value of
	/// enqueue(), which is ActiveResult<int>. See the ActiveResult class
	/// template for more information. The second one is by using the functions
	/// of AsyncIOCommand, such as wait(), succeeded() and result().
	///
	/// AsyncIOChannel supports the operations write, read and seek directly. However,
	/// subclasses of AsyncIOChannel can define additional operations.
{
public:
	ActiveMethod<int, AsyncIOCommand::Ptr, AsyncIOChannel, ActiveStarter<ActiveDispatcher> > enqueue;
		/// Actual signature: 
		///     int enqueueImpl(const AsyncIOCommand::Ptr& pCommand);
		///
		/// Enqueue the given command for eventual execution.
		/// Returns the number of bytes read or written if the operation
		/// was successful.

	BasicEvent<AsyncIOEvent> commandCompleted;
		/// Fired when a command has successfully completed.
		
	BasicEvent<AsyncIOEvent> commandFailed;
		/// Fired when a command has failed.

	virtual int write(const void* buffer, int length);
		/// Write length bytes from buffer. 
		///
		/// Must be overridden by subclasses. The default implementation 
		/// throws a NotImplementedException.
		///
		/// Returns the number of bytes written.
		
	virtual int read(void* buffer, int length);
		/// Read up to length bytes into buffer. 
		///
		/// Must be overridden by subclasses. The default implementation 
		/// throws a NotImplementedException.
		///
		/// Returns the number of bytes read.
		
	virtual int seek(std::streamoff off, std::ios::seekdir dir);
		/// Sets the current read/write position.
		/// 
		/// Must be overridden by subclasses. The default implementation 
		/// throws a NotImplementedException.
		///
		/// Always returns 0.
		
protected:
	AsyncIOChannel();
		/// Creates the AsyncIOChannel.
		
	~AsyncIOChannel();
		/// Destroys the AsyncIOChannel.
	
	int enqueueImpl(const AsyncIOCommand::Ptr& pCommand);
		/// Execute the given command by calling
		///     pCommand->execute(this);
		/// and return the result.
	
private:
	AsyncIOChannel(const AsyncIOChannel&);
	AsyncIOChannel& operator = (const AsyncIOChannel&);
};


} // namespace Poco


#endif // Foundation_AsyncIOChannel_INCLUDED