FSM Lang : simpleCommunicator

This machine manages communications using a "stop and wait" protocol. Only one message is allowed to be outstanding.

	SEND_MESSAGE	ACK
IDLE	sendMessage returns: noEvent transition : AWAITING_ACK Since we're idle, we can simply send the message. Transitioning to the AWAITING_ACK state ensures that any other messages we're asked to send will be queued.	transition : none
AWAITING_ACK	queueMessage returns: noEvent transition : none Since we're busy, we must queue the message for later sending. The queue will be checked when the ACK is received.	checkQueue returns: SEND_MESSAGE noEvent transition : IDLE We've received our ACK for the previous message. It is time to check for any others.

SEND_MESSAGE

ACK

IDLE

sendMessage
returns:

noEvent

transition : AWAITING_ACK

Since we're idle, we can simply send the message. Transitioning to the AWAITING_ACK state ensures that any other messages we're asked to send will be queued.

transition : none

AWAITING_ACK

queueMessage
returns:

noEvent

transition : none

Since we're busy, we must queue the message for later sending. The queue will be checked when the ACK is received.

checkQueue
returns:

SEND_MESSAGE
noEvent

transition : IDLE

We've received our ACK for the previous message. It is time to check for any others.

Actions
sendMessage	sendMessage sends a message from the queue. The message is expected to be there, since checkQueue will have been previously called. Returns: noEvent
queueMessage	queueMessage adds a message to the queue Returns: noEvent
checkQueue	checkQueue only checks; it does not dequeue; that is done by sendMessage. Return SEND_MESSAGE when the queue is not empty. Returns: SEND_MESSAGE noEvent