/*#*
*#* $Log$
+ *#* Revision 1.6 2005/01/22 04:20:26 bernie
+ *#* Write extensive documentation; Add simple locking.
+ *#*
*#* Revision 1.5 2004/11/28 23:20:25 bernie
*#* Remove obsolete INITLIST macro.
*#*
#include <mware/list.h>
+/*!
+ * Handle queues of messages associated an action.
+ *
+ * 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.
+ *
+ * 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;
+ *
+ *
+ * // 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(&reply_port,
+ * event_createSignal(proc_current(), SIGF_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);
+ *
+ * // 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, &msg1);
+ *
+ * // Wait for a reply...
+ * sig_wait(SIG_SINGLE);
+ *
+ * reply = (TestMsg *)msg_get(&test_reply_port);
+ * ASSERT(reply != NULL);
+ * ASSERT(reply->result == 5);
+ *
+ * // Get reply to second message.
+ * while (!(reply = (TestMsg *)msg_get(&test_reply_port))
+ * {
+ * // 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(), SIGF_EXAMPLE);
+ *
+ * proc_new(sender_proc, (iptr_t)&test_port,
+ * sender_stack, sizeof(sender_stack);
+ *
+ * for (;;)
+ * {
+ * sigmask_t sigs = sig_wait(SIGF_EXAMPLE | more_signals);
+ *
+ * if (sigs & SIGF_EXAMPLE)
+ * {
+ * TestMsg *emsg;
+ * while (emsg = (TestMsg *)msg_get(&test_port)
+ * {
+ * // Do something with the message
+ * emsg->result = emsg->x + emsg->y;
+ * msg_reply((Msg *)msg);
+ * }
+ * }
+ * }
+ * }
+ * \end code
+ */
typedef struct MsgPort
{
- List queue; /*!< Messages queued at this port */
- Event evn; /*!< Event to trigger when a message arrives */
+ 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 */
+ 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(MsgPort *port)
+{
+ proc_forbid();
+}
+
+/*!
+ * Unlock a message port.
+ *
+ * \see msg_lockPort()
+ */
+INLINE void msg_unlockPort(MsgPort *port)
+{
+ proc_permit();
+}
+
+
/*! Initialize a message port */
-INLINE void msg_initPort(MsgPort* port, Event event)
+INLINE void msg_initPort(MsgPort *port, Event event)
{
LIST_INIT(&port->queue);
- port->evn = event;
+ port->event = event;
}
/*! Queue \a msg into \a port, triggering the associated event */
-INLINE void msg_put(MsgPort* port, Msg* msg)
+INLINE void msg_put(MsgPort *port, Msg *msg)
{
+ msg_portLock(port);
ADDTAIL(&port->queue, &msg->link);
- event_do(&port->evn);
+ msg_portUnlock(port);
+
+ event_do(&port->event);
}
-/* Get the first message from the queue of \a port, or NULL if the port is empty */
-INLINE Msg* msg_get(MsgPort* port)
+/*!
+ * 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)
{
- return (Msg*)REMHEAD(&port->queue);
+ Msg *msg;
+
+ msg_portLock(port);
+ msg = (Msg *)REMHEAD(&port->queue);
+ msg_portUnlock(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_portLock(port);
+ msg = (Msg *)port->queue.head;
if (ISLISTEMPTY(&port->queue))
- return NULL;
+ msg = NULL;
+ msg_portUnlock(port);
- return (Msg *)port->queue.head;
+ return msg;
}
-/*! Send back (reply) \a msg to its sender */
-INLINE void msg_reply(Msg* msg)
+/*! Send back (reply) \a msg to its sender. */
+INLINE void msg_reply(Msg *msg)
{
msg_put(msg->replyPort, msg);
}
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