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bertos/kern/msg.h

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+/**
+ * \file
+ * <!--
+ * This file is part of BeRTOS.
+ *
+ * Bertos 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 St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * As a special exception, you may use this file as part of a free software
+ * library without restriction.  Specifically, if other files instantiate
+ * templates or use macros or inline functions from this file, or you compile
+ * this file and link it with other files to produce an executable, this
+ * file does not by itself cause the resulting executable to be covered by
+ * the GNU General Public License.  This exception does not however
+ * invalidate any other reasons why the executable file might be covered by
+ * the GNU General Public License.
+ *
+ * Copyright 2004 Develer S.r.l. (http://www.develer.com/)
+ * Copyright 1999,2001 Bernie Innocenti <bernie@codewiz.org>
+ *
+ * -->
+ *
+ *
+ * \defgroup kern_msg Message box IPC
+ * \ingroup kern
+ * \{
+ *
+ * \brief Simple inter-process messaging system
+ *
+ * This module implements a common system for executing
+ * a user defined action calling a hook function.
+ *
+ * A message port is an abstraction used to exchange information
+ * asynchronously between processes or other entities such as
+ * interrupts and call-back functions.
+ *
+ * This form of IPC is higher-level than bare signals and
+ * semaphores, because it sets a policy for exchanging
+ * structured data with well-defined synchronization and
+ * ownership semantics.
+ *
+ * Before using it, a message port must be initialized by
+ * calling msg_initPort(), which associates the port with
+ * an Event object, which can be setup to signal a process
+ * or invoke a call-back hook.
+ *
+ * A process or interrupt routine can deliver messages to any
+ * message port by calling msg_put().  By sending a message,
+ * the sender temporarly or permanently transfers ownership
+ * of its associated data to the receiver.
+ *
+ * Queuing a message to a port automatically triggers the
+ * associated Event to notify the receiver.  When the
+ * receiver wakes up, it usually invokes msg_get() to pick
+ * the next message from the port.
+ *
+ * \note
+ * When you put a message into a port, such message becomes
+ * unavailable until you retrieve it using msg_get(), eg.
+ * you must not delete it or put it into another port.
+ *
+ * Message ports can hold any number of pending messages,
+ * and receivers usually process them in FIFO order.
+ * Other scheduling policies are possible, but not implemented
+ * in this API.
+ *
+ * After the receiver has done processing a message, it replies
+ * it back to the sender with msg_reply(), which transfer
+ * ownership back to the original sender.  Replies are delivered
+ * to a reply port, which is nothing more than another MsgPort
+ * structure designated by the sender.
+ *
+ * Returning messages to senders is not mandatory, but it provides
+ * a convenient way to provide some kind of result and simplify
+ * the resource allocation scheme at the same time.
+ *
+ * When using signals to receive messages in a process, you
+ * call sig_wait() in an event-loop to wake up when messages
+ * are delivered to any of your ports.  When your process
+ * wakes up with the port signal active, multiple messages
+ * may already have queued up at the message port, and the
+ * process must process them all before returning to sleep.
+ * Signals don't keep a nesting count.
+ *
+ * A simple message loop works like this:
+ *
+ * \code
+ *	// Our message port.
+ *	static MsgPort test_port;
+ *
+ *	// A test message with two parameters and a result.
+ *	typedef struct
+ *	{
+ *		Msg msg;
+ *
+ *		int x, y;
+ *		int result;
+ *	} TestMsg;
+ *
+ *
+ *  PROC_DEFINE_STACK(sender_stack, KERN_MINSTACKSIZE);
+ *
+ *	// A process that sends two messages and waits for replies.
+ *	static void sender_proc(void)
+ *	{
+ *		MsgPort test_reply_port;
+ *		TestMsg msg1;
+ *		TestMsg msg2;
+ *		Msg *reply;
+ *
+ *		msg_initPort(&test_reply_port,
+ *			event_createSignal(proc_current(), SIG_SINGLE);
+ *
+ *		// Fill-in first message and send it out.
+ *		msg1.x = 3;
+ *		msg1.y = 2;
+ *		msg1.msg.replyPort = &test_reply_port;
+ *		msg_put(&test_port, &msg1.msg);
+ *
+ *		// Fill-in second message and send it out too.
+ *		msg2.x = 5;
+ *		msg2.y = 4;
+ *		msg2.msg.replyPort = &test_reply_port;
+ *		msg_put(&test_port, &msg2.msg);
+ *
+ *		// Wait for a reply...
+ *		sig_wait(SIG_SINGLE);
+ *
+        reply = containerof(msg_get(&test_reply_port), TestMsg, msg);
+ *		ASSERT(reply != NULL);
+ *		ASSERT(reply->result == 5);
+ *
+ *		// Get reply to second message.
+ *		while (!(reply = containerof(msg_get(&test_reply_port), TestMsg, msg)))
+ *		{
+ *			// Not yet, be patient and wait some more.
+ *			sig_wait(SIG_SINGLE);
+ *		}
+ *
+ *		ASSERT(reply->result == 9);
+ *	}
+ *
+ *
+ *	// Receive messages and do something boring with them.
+ *	static void receiver_proc(void)
+ *	{
+ *		msg_initPort(&test_port,
+ *			event_createSignal(proc_current(), SIG_EXAMPLE);
+ *
+ *		proc_new(sender_proc, NULL,sizeof(sender_stack), sender_stack);
+ *
+ *		for (;;)
+ *		{
+ *			sigmask_t sigs = sig_wait(SIG_EXAMPLE | more_signals);
+ *
+ *			if (sigs & SIG_EXAMPLE)
+ *			{
+ *				TestMsg *emsg;
+ *				while((emsg = containerof(msg_get(&test_port), TestMsg, msg)))
+ *				{
+ *					// Do something with the message
+ *					emsg->result = emsg->x + emsg->y;
+ *					msg_reply(emsg->msg);
+ *				}
+ *			}
+ *		}
+ *	}
+ * \endcode
+ *
+ * \author Bernie Innocenti <bernie@codewiz.org>
+ *
+ * $WIZ$ module_name = "msg"
+ * $WIZ$ module_depends = "event", "signal", "kernel"
+ */
+
+
+#ifndef KERN_MSG_H
+#define KERN_MSG_H
+
+#include <mware/event.h>
+#include <struct/list.h>
+#include <kern/proc.h>
+
+typedef struct MsgPort
+{
+	List  queue;   /**< Messages queued at this port. */
+	Event event;   /**< Event to trigger when a message arrives. */
+} MsgPort;
+
+
+typedef struct Msg
+{
+	Node     link;      /**< Link into message port queue. */
+	MsgPort *replyPort; /**< Port to which the msg is to be replied. */
+	/* User data may follow */
+} Msg;
+
+
+/**
+ * Lock a message port.
+ *
+ * This is required before reading or manipulating
+ * any field of the MsgPort structure.
+ *
+ * \note Ports may be locked multiple times and each
+ *       call to msg_lockPort() must be paired with
+ *       a corresponding call to msg_unlockPort().
+ *
+ * \todo Add a configurable policy for locking against
+ *       interrupts and locking with semaphorse.
+ *
+ * \see msg_unlockPort()
+ */
+INLINE void msg_lockPort(UNUSED_ARG(MsgPort *, port))
+{
+	proc_forbid();
+}
+
+/**
+ * Unlock a message port.
+ *
+ * \see msg_lockPort()
+ */
+INLINE void msg_unlockPort(UNUSED_ARG(MsgPort *, port))
+{
+	proc_permit();
+}
+
+
+/** Initialize a message port */
+INLINE void msg_initPort(MsgPort *port, Event event)
+{
+	LIST_INIT(&port->queue);
+	port->event = event;
+}
+
+/** Queue \a msg into \a port, triggering the associated event */
+INLINE void msg_put(MsgPort *port, Msg *msg)
+{
+	msg_lockPort(port);
+	ADDTAIL(&port->queue, &msg->link);
+	msg_unlockPort(port);
+
+	event_do(&port->event);
+}
+
+/**
+ * Get the first message from the queue of \a port.
+ *
+ * \return Pointer to the message or NULL if the port was empty.
+ */
+INLINE Msg *msg_get(MsgPort *port)
+{
+	Msg *msg;
+
+	msg_lockPort(port);
+	msg = (Msg *)list_remHead(&port->queue);
+	msg_unlockPort(port);
+
+	return msg;
+}
+
+/** Peek the first message in the queue of \a port, or NULL if the port is empty. */
+INLINE Msg *msg_peek(MsgPort *port)
+{
+	Msg *msg;
+
+	msg_lockPort(port);
+	msg = (Msg *)port->queue.head.succ;
+	if (LIST_EMPTY(&port->queue))
+		msg = NULL;
+	msg_unlockPort(port);
+
+	return msg;
+}
+
+/** Send back (reply) \a msg to its sender. */
+INLINE void msg_reply(Msg *msg)
+{
+	msg_put(msg->replyPort, msg);
+}
+
+/** \} */ //defgroup kern_msg
+
+int msg_testRun(void);
+int msg_testSetup(void);
+int msg_testTearDown(void);
+
+#endif /* KERN_MSG_H */