CMSC 417 Programming Assignment #3
Due October 29, 1999 (5:00 PM)
Introduction
In this project, you will implement a link state routing system. Each node in the network will be connected
to one or more other nodes. Using hello packets and bounded flooding, you will implement a system to
inform all of the nodes in the network of the current network topology. Each node will also build a routing
table that minimizes the number of hops to all other nodes in the network.
This project will be the first introduction to several key ideas that will be used later in the semester. It will
also combine what you have learned (and probably most of the code) from projects one and two.
Timers
A key building block for this project will be the timer thread. By using the timer thread, you will be able to
cause events to happen in your system at specific times in the future (for example sending hello packets at a
fixed interval of time).
The implementation for the timer thread will be via the queue abstraction you built for project two. When a
thread wishes to schedule an event in the future, it enqueue’s a request to the timer thread. When the re-
quested time interval has elapsed, the timer thread enqueues a message indicating that the time interval has
finished.
The interface for a thread that wishes to use the timer thread is:
int createAlarm(int expireTime, Queue *respQueue, bool repeats)
Create a new alarm that will enqueue a response into the queue respQueue expireTime milli-
seconds in the future. If the repeats parameter is true, it will en-queue a response every ex-
pireTime milliseconds until canceled. If the return value is positive, it contains the unique identi-
fier of the alarm event, and if it is negative it indicates an error in creating the alarm.
void cancelAlarm(int alarmId)
Cancel the passed alarm. It is possible that one or more alarm notifications may occur after the
alarm is canceled due to alaram events passing the cancelAlarm request in different queues.
Note: Alarm Ids should be globally unique and will likely be allocated in the context of the application
thread making the request. If this is the case, don’t forget to use synchronization (e.g. mutex’s) around the
update of the alarm ids.
Messages
In this project you will need to exchange messages between different threads in your system. In order to
allow a single thread to respond to a variety of different message types such as a timer event or the arrival of
a data packet, you will need to define a common message format to pass via the queues. Each message
should start with an integer field that indicates the type of the message (e.g. TIMER_REQ, TIMER_ACK,
TIMER_EXPIRE, etc.). In addition, each message can contain a variety of parameters that are specific to
