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# C语言代写 | COMP2401 – Assignment #5

### C语言代写 | COMP2401 – Assignment #5

COMP2401 – Assignment #5
(Due: Sun. Mar 29, 2020 @ 6pm)
The next page shows a screenshot of what the city will look like when printed. Notice that each of the
6 city areas has a name as well as a fixed (x,y) location and is displayed as a large circle of a certain
color. The smaller circles are moving taxis. A taxi will have the same color as a city area if it is on
its way there to drop off a customer. A taxi will be black if it is picking up a customer and white if it is
available and waiting for a customer. Each taxi has a 3-digit plate number as its ID. Each city area is
actually just an index from 0 to 5. An index of -1 will represent an UNKNOWN_AREA.
Ideally, it would be nice to see a map of the city, but we kept it simple and just chose 6 circles to
represent pickup and dropoff areas of the city.
As the program runs, the taxis
will travel back and forth from
one city area to another, as
customers are picked up and
dropped off. The travel time
estimates from one area of the
city to another area is defined
by this figure. Note that taxis
may pickup and drop off a
customer in the same area, but
this still takes 10 minutes. This
diagram has been hard-coded
into a constant 2D array which
is also defined in the
simulator.h file as follows.
Make sure that you understand
it.
const char TIME_ESTIMATES[NUM_CITY_AREAS][NUM_CITY_AREAS] =
{{10, 20, 40, 40, 20, 20},
{20, 10, 20, 20, 20, 40},
{40, 20, 10, 40, 40, 60},
{40, 20, 40, 10, 20, 20},
{20, 20, 40, 20, 10, 20},
{20, 40, 60, 20, 20, 10}};
A dispatch center is defined as follows:
typedef struct {
char online; // 0 = no, 1 = yes
Taxi *taxis[MAX_TAXIS]; // the taxis belonging to this dispatch center
int numTaxis; // the number of taxis in the dispatch center
Request requests[MAX_REQUESTS]; // customer requests
int numRequests; // number of customer requests in the system
} DispatchCenter;
Notice that it is basically two arrays … one for taxis and one for pending customer requests. Each of
these is set to be a maximum of 100 in size, but the numTaxis and numRequests should indicate
the actual number at any moment. numTaxis will remain constant in our program, whereas
numRequests will vary over time.
Each Request is just two small numbers indicating where the customer wants
to be picked up and where he/she wants to be dropped off as follows:
typedef struct {
char pickupLocation; // City area to be picked up in (0 to NUM_CTY_AREAS)
char dropoffLocation; // City area to be dropped off in (0 to NUM_CTY_AREAS)
} Request;
Each Taxi has a unique pID (i.e., process id, since each will run as a separate process). A Taxi also
has a unique plate number (0 to numTaxis) and their current (x,y) location in the city at any time. A
taxi has a status of being either AVAILABLE, PICKUP_UP someone or DROPPING_OFF someone.
The currentArea is the area that the taxi is currently in. The pickupArea is the area that the taxi is
on the way to in order to get the customer and the dropoffArea is the area that the customer is to be
dropped off at. Each of these areas is a number from 0 to NUM_CITY_AREAS or set to
UNKNOWN_AREA. Finally, the eta is the estimated time of arrival to the pickup or destination area:
typedef struct {
int pID; // process ID for this taxi
int x; // x location of the taxi
int y; // y location of the taxi
short plateNumber; // unique plate id for taxi
char status; // AVAILABLE, PICKING_UP, or DROPPING_OFF
char currentArea; // index of city area currently in
char pickupArea; // index of city area to pick up person in
char dropoffArea; // index of city area to drop off person in
short eta; // time left until reaching destination
} Taxi;
(2) The simulator.c file contains the code for the main application. You need to add code so that the
function does the following:
• It should dynamically-allocate a single Taxi and store it in the dispatch center. The new taxi
should be placed in a random area of the city (i.e., in the center of one of the city area
circles) and have plate number 0. The currentArea of the taxi should be set to that area,
while the pickup/dropoff areas should be UNKNOWN_AREA. New taxis should start off
being available for customers.
• It must use fork() to start a new process for that taxi … calling the runTaxi() function in the
taxi.c file … passing newly created taxi as its parameter. Upon returning from the
runTaxi() function, the taxi process should simply exit.
• It should spawn a thread to handle incoming requests. This thread should call the
handleIncomingRequests() function in the dispatchCenter.c file and pass in a pointer to
• It should spawn a thread to handle the displaying of the city. This thread should call the
showSimulation() function in the display.c file and pass in a pointer to the
• The code should then wait for the request-handling thread to complete and it should then
kill all running taxi processes.
• The code should free all allocated memory so that valgrind shows no leaks.
The showSimulation() function (in the display.c file) has been completed for you. You MUST
NOT alter any code in the display.c file. Use the makefile that was given to you to compile
everything. Once you have this step completed, run the simulator in the background (i.e., use &).
Make sure that you see the screen snapshot (on the previous page) appear … showing the city
areas and a single taxi in one of the areas. Once you see this, you can be sure that the display
thread is working properly. Type ps in the terminal window. You should see two processes
labelled simulator. That is because you have a taxi process running with the same name. When
you close the window, you should see some XIO error (don’t worry about this). After closing the
window, you can type ps again … you should see that one simulator process is no longer running,
but you will likely see the taxi process (also called simulator) still running. You should kill this
process in the terminal using kill followed by the process id.
(3) Write code in the handleIncomingRequests() function (from dispatchCenter.c) so that it first
starts up a server and then goes into an infinite loop that repeatedly waits for incoming user
requests and handles them. The idea is that taxis will communicate with the server to ask for a
customer to pickup. When the server receives a REQUEST_CUSTOMER command from a taxi,
it should check to see if there is a customer request available in its requests buffer. If not, the taxi
should be told that no request is available. Otherwise, the taxi should be given the pickup and
dropoff location for the customer … and this customer request should be removed from the
request buffer so that no other taxis get that request. While on route to pickup or drop off the
customer … the taxi will send an UPDATE command to the server along with its plate number,
current x and y location, status and the dropoffArea. These should be recorded at the dispatch
center so that the dispatch center always has each taxi’s latest information. Customers will send
a REQUEST_TAXI command to the server which will contain the requested pickup and dropoff
locations as city area indices. If the maximum number of requests has been reached, the
customer should be told that the request cannot be handled. Otherwise, it should be told that all is
ok and the request should be added to the buffer. Requests should always be handled on a firstcome-first-served basis. Finally, a SHUTDOWN command should cause the server to go off line
(gracefully) when it is received. Make sure the code compiles, but you cannot test it until you do
the next step.
(4) Complete the code in the stop.c file so that it attempts to shut down the dispatch center server by
sending the SHUTDOWN command to it. Test your code by running the simulator server in the
background and then running the stop program. If all works well, the simulator window should
close and should shut down gracefully. Use ps to make sure that the simulator has indeed shut
down properly as well as the stop program. Make sure that you don’t have any segmentation
faults.
(5) Complete the runTaxi() function in the taxi.c file so that it runs in an infinite loop. If the taxi is
available, it should contact the dispatch center to get a request. If it is busy picking up or
dropping off a customer, it should send updates to the dispatch center. A delay has been added
to the loop so that it does not overwhelm the server with many requests. Here is how to do these
two steps (you may want them done as helper functions):
a. To request a customer from the dispatch center, the taxi should first attempt to connect to
the dispatch center and then if successful, it should send the REQUEST_CUSTOMER
command. If the server responds with a YES, then the taxi should handle the customer
request as follows:
i. If the pickup area is the same as the area the taxi is currently in, assume that the
pickup is immediate. Then the taxi just needs to head to the dropoff area. The
taxi’s currentArea, pickupArea and dropoffArea should all be set properly and the
taxi should be in DROPPING_OFF mode. The estimated time of arrival (eta) should
be set accordingly based on the 2D TIME_ESTIMATES array from the pickupArea
to the dropoffArea.
ii. If the pickup area is different from the area that the taxi is currently in, then the taxi
should go into PICKING_UP mode. Make sure to set the pickupArea and
dropoffArea accordingly. The eta should be set according to the time it takes to get
from the currentArea to the pickupArea.
b. To send an update to the dispatch center, the taxi should first attempt to connect to the
dispatch center and then if successful, it should send the UPDATE command along with its
(x,y) location, plate number, status and dropoffArea.