COMP2401 - Assignment #5
(Due: Monday, November 30th, 2020 @ 6pm)
In this assignment, you will make a simulator for simple robots that uses multiple threads and allows
multiple robots to connect to it … with each robot running as its own process.
To begin this assignment, you should download the following files:
makefile – use this to compile
simulator.h – contains definitions and structs that will be used throughout your code
environmentServer.c – contains a template for the code that will run the environment server
display.c – contains the window/drawing code that you will use to display the robots
stop.c – contains a template for the code for a process that will stop the simulator
robotClient.c – contains a template for the code for a process that will run a single robot
When compiling the files, you will need to include the -lm -lpthread and -lX11 libraries.
(but the -lX11 library (which is “minus L X eleven”) is only needed for the environmentServer.c file
since it uses a window and graphics.
Follow the steps below (in order) to complete the assignment:
(1) Examine the simulator.h file. The robots have a radius of ROBOT_RADIUS. Each robot is
represented as an (x,y) location and a direction. The x and y values are the location of the
robot in the window … which will be in the range from ROBOT_RADIUS to (ENV_SIZE -
ROBOT_RADIUS). The direction should always be in the range from -180° to +180°. Each
time a robot moves forward, it moves ROBOT_SPEED pixels in the direction that it is facing.
Each time a robot turns, it turns ±ROBOT_TURN_ANGLE degrees. The Environment
contains up to MAX_ROBOTS robots in an array. numRobots is the number of robots
currently registered with the server. The shutDown flag indicates whether or not the
environment has been shut down, it must be set to 0 upon startup.
(2) The environmentServer.c file contains the code for the server template. The main function
in this file MUST spawn two threads … one that will repeatedly accept incoming client requests
… and another that will repeatedly redraw the robots in the window. Both of these threads
should continue until the shutDown flag in the Environment has been set and all registered
robotClients have been informed of the shutdown … at which point the threads will each exit
gracefully. A pointer to the Environment should be passed in when spawning the threads so
that the threads have access to the robots and the shutDown flag.
Write the code so that the two threads call these two functions, respectively:
void *handleIncomingRequests(void *environment)
void *redraw(void *environment)
The redraw() function is in the display.c file and has been completed for you. You MUST
NOT alter any code in the display.c file. When you compile and run the
environmentServer.c file, you should see a window come up which is empty. Run it in the
background (i.e., use &) and then type ps in the terminal window to see the process id. When
you close the window, you should see some XIO error (don’t worry about this). Then typing
ps, you should see that the environmentServer is no longer running.
Write the code in the handleIncomingRequests() function so that it starts up the server and
repeatedly waits for incoming client requests. There are four possible incoming requests
defined by the definitions in the simulator.h file: (1) REGISTER, (2) STOP, (3)
CHECK_COLLISION and (4) STATUS_UPDATE,. For now, write code that accepts an
incoming request to STOP the environmentServer. The code MUST be based on the UDP
version of the client/server sockets that were discussed in the notes (i.e., not TCP). The
incoming command for STOP should come in as a single byte. Upon receiving it, the server
should shut down gracefully and both threads should be stopped cleanly.
Complete the code in the stop.c file so that it attempts to connect to the server and send the
STOP command to the server. Test your code by running the environmentServer in the
background and then running the stop program. If all works well, the environmentServer
window should close and should shut down gracefully. Use ps to make sure that the
environmentServer has indeed shut down properly as well as the stop program. Make sure
that you don’t have any segmentation faults.
(3) Now add code to the robotClient.c file so that it attempts to register with the running
environmentServer. To do this, it should send a REGISTER command byte . It should then
wait for a response from the server that should contain an OK or NOT_OK byte response. If
the response byte was OK, then additional bytes should be received containing the id of the
robot (i.e., its number in the environment array of robots), a randomly chosen (x, y) position
and a randomly chosen direction. Note that it is the environmentServer that should choose
the random location and direction (see step (1) above for valid ranges). If you are setting up
the send/receive buffer as unsigned bytes, you will need to split the x, y and direction values
into high and low bytes. You may also want to have an extra byte to indicate the sign of the
direction (i.e., positive or negative) since the magnitude will be 0 to 180. You will need to
adjust the handleIncomingRequests() function in the environmentServer.c file so that it
sends the appropriate bytes back to the client. When all is working, you should see the robot
appear in the simulator window. You’ll need to run the environmentServer first (in the
background) and then run the robotClient process (also in the background). Once it works,
try running a second and third robotClient process … you should see 2 and then 3 robots
appearing. Make sure that the stop process still shuts down the server properly.
(4) There is a limit to how many robots that can be added. It is set as MAX_ROBOTS, which is 20
by default. Adjust the code in the simulator server to deny any registrations that go beyond
this limit. Simply send a NOT_OK response when it is full to capacity. Make sure that the
robotClient handles this response properly. Test everything by adding 20 robots and then try
adding a 21st robot. Make sure that you display an appropriate error message in the
robotClient code so that it is clear when the client is unable to register. Don’t test this yet
until you get the automatic shutdown of your robotClients because otherwise you will need to
kill 20 processes manually!!
(5) Now we will add functionality to the robotClient so that it repeatedly moves the robot around
in the environment indefinitely. To move forward, the robot should first ensure that if it moves
forward, it will not collide with any other robots or the environment boundary. To do this, you
should send a CHECK_COLLISION request to the server which should contain the following
information: the CHECK_COLLISION command, the robot’s ID, the current location and
direction of the robot. Keep in mind that if you use unsigned char array to send the bytes, you
will need to break down the x, y into two bytes (most significant byte and least significant byte).
You will also need to be careful sending the direction (which is ±180°) since an unsigned char
only stores values in the 0-255 range and a signed char in the -128 to +127 range.
The robot should receive a single byte back from the server which has one of 4 values:
1. OK if the robot can move to that location without problems,
2. NOT_OK_BOUNDARY if the robot cannot move to that location because it would go
outside the boundary of the environment, and
3. NOT_OK_COLLIDE if the robot cannot move to that location because it would collide
with another robot.
4. LOST_CONTACT if the server is trying to shut down and the robot client needs to quit.
If all is OK, the robot should move forward by calculating a new location based on its current
location and direction as follows: (newX, newY) = (x+S*cos(d), y+S*sin(d)) where (x,y) is the
current robot location, S is the robot’s speed (in pixels) and d is the robot’s direction.
Otherwise, the robot should turn left or right (chosen randomly) by ROBOT_TURN_ANGLE
degrees. To do this, do not change the (x,y) location, just change the direction. Make sure
that the direction always remains in the ±180° range. Also, set your code up so that when the
robot first hits a boundary or collides with another robot, it computes the random direction to
turn towards (CW or CCW). If the robot is unable to move on any successive turns, it should
continue to turn in the SAME direction again. It should keep turning ROBOT_TURN_ANGLE
degrees once per loop iteration. Only when it is OK to move forward should it begin its
forward movement again. Coding things in this manner will ensure that the robot does not
alternate turning back and forth in what appears to be an indecisive pattern. If coded properly,
you should see the robot turning little by little upon collision.
(6) Add code to the robotClient so that it repeatedly sends STATUS_UPDATE messages to the
server. These messages just send the latest robot location and direction so that the server
knows where the robot is at all times. This allows the server to display it and is also
necessary for collision detection later on. There should be no response back from the server
when a STATUS_UPDATE is sent.
(7) You will notice after stopping, that some robotClient processes will still be running. You
should kill these processes. You need to adjust your code so that all robotClient processes
shut down automatically when the environmentServer shuts down. To do this, when the
environmentServer gets a STOP request … it should not stop right away, but instead it
should start informing the registered robotClients that the server is about to shut down.
Since the robotClients are not in a loop listening for messages from the server, you will want
to send a LOST_CONTACT response to each robotClient when it does a
CHECK_COLLISION request. When a robotClient received such a response, it should shut
itself down.
(8) To make things work, you will need to adjust the handleIncomingRequests() function in the
environmentServer.c file so that it handles incoming CHECK_COLLISION requests from the
robots. It will need to receive all the incoming data that was sent to it as part of the
CHECK_COLLISION request. Write a function that determines whether or not the robot can
move forward from the given location without collision. It will need to check the boundary
values as well as the locations of all other robots to decide whether to return a value of OK,
NOT_OK_BOUNDARY or NOT_OK_COLLIDE. You will also need to handle incoming
STATUS_UPDATE requests so that you know (and update) the position of all robots at all
times. Do NOT alter the display.c file, nor the simulator.h file.
(9) Test your code with a single robot to see if it works properly. You can lengthen the usleep()
delays to slow things down and investigate the movements, but you must put them back to
their initial values when things seem to be working properly. Test everything with multiple
robots and ensure that the moving and collisions are working properly. You might end up with
robots stuck on each other … see the next part as a possible explanation,
(10) When registering many robots, each is given an initial start location. Sometimes, the
location of one robot may overlap with the location of another robot and the two can get stuck
together. Adjust the handleIncomingRequests() function in the environmentServer.c file so
that it ensures that each robot is placed a unique non-overlapping location in the environment.
That is, make sure that the robot can “move to” (i.e., or be initially placed at) the randomly
chosen location. You might want to use a WHILE loop until a good random location is found.
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IMPORTANT SUBMISSION INSTRUCTIONS:
Submit all of your c source code files as a single tar file containing:
1. A Readme text file containing
your name and studentNumber
a list of source files submitted
any specific instructions for compiling and/or running your code
2. All of your .c source files and all other files needed for testing/running your programs.
3. Any output files required, if there are any.
The code MUST compile and run on the course VM.
If your internet connection at home is down or does not work, we will not accept this as a reason for
handing in an assignment late ... so make sure to submit the assignment WELL BEFORE it is due !
You WILL lose marks on this assignment if any of your files are missing. So, make sure that you hand
in the correct files and version of your assignment. You will also lose marks if your code is not written
neatly with proper indentation and containing a reasonable number of comments. See course
notes for examples of what is proper indentation, writing style and reasonable commenting).
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