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C语言代写 | CSI3131 Assignment 1 Winter 2020

C语言代写 | CSI3131 Assignment 1 Winter 2020

Assignment 1 Winter 2020
Process/thread creation and inter-process communication
1. process creation in Linux using fork() and exec() system calls
2. thread creation in Linux with the pthread API
3. inter-process communication using pipes
Posted: Jan 30, 2020
Due: Feb 13, 2020, 23:59
Description (Please read the complete assignment document before starting.)
Two programs have been provided: user.c and router.c. Your task shall be to complete
these two programs such that the execution of the program user creates three processes as

1. User process: this is the original process invoked when user is run. It is
responsible for creating the other two processes after which is simulates User that
asks time to Server (simulated by the Server process).
2. Server process: this is a child process of the User process that simulates
responding the commands from User and displaying time in a thread.
3. Router process: This process is executed by User and forwards any kind of data
from User and Server process to each other.
4. Message Flow: User sends ‘t’ to Server and Server responds with current time.
User sends ‘q’ to Server and Server should be ended by itself. These commands
should be forwarded by Router process. Server and User should not communicate
with each other directly by any means.
The User and Server processes use 2 pipes to communicate with router respectively.
0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6
Pipe User to Router
Pipe Router to User
Pipe Router to Server
Pipe Server to Router
Their scheme should be implemented as following figure. First User creates the Router
and Server process. And Server immediately creates a thread to print time every few
seconds. Then User sends ‘t’ command to Router and Router forwards the command to
Server. Once Serve receives the ‘t’ command, it should reply current time immediately.
After User queries time for several times, it sends ‘q’ command to Server. And Server
should identify this command and kill the thread and end itself. Then User will kill the
Router process by using kill() and end up itself.
User Router Server
PrintTimeInfo TimeInfo
Server Thread
PrintS Time Info serveral times
Create a Thread
q Server Quits
Kill Router
To complete the assignment:
1. Start with the provided files user.c and router.c. Complete the documentation in each
file to indicate your name and student number. Take the time to document well your
code. Consider taking the time to design your code before you start coding.
2. Utility functions has been given including:
a. TimeInfo structure containing hour, minute, and second. It should be initialized by
b. closePipe
c. getTimeInfo, which is used for get current TimeInfo
d. printTimeInfo, which is to print the content of a TimeInfo
e. printTime, which prints current time
f. blockRead, which provides the read function using block mode and will not influent the read
function in the system
3. The programs should be compiled using the command make.
4. To submit the assignment, upload the files user.c and server.c. Do not forget to click
on the submit button after (and only after) you have uploaded the file.
5. See point 4 in “Background Information” for hints on how to observe
processes/threads and pipes to help debug your programs.
6. When user is run, the following output should appear on your screen (Note that PIDs
shall be specific to your execution).
There are 10 functions you should implement in your code to get points, which is also
mentioned in the comments. (10 marks each)
a. Server process should create a thread to display current time for at least 2 times
b. Server should respond the following command from Router
-“t”: send current time to the router
-“q”: stop waiting for the command, kill thread and exit.
c. Server should end the process by itself instead of User process
d. User queries time for at least 2 times by sending ‘t’ command to Router
e. Then User sends ‘q’ command to Router
f. User waits for the Server ending itself
g. User kills the Router process
h. Router connects with User and Server via pipes
i. Router receives any data from User and forwards the data to the Server
j. Router receives any data from Server and forwards the data to the User
Output Sample
Background information:
1. An open file descriptor is an integer, used as a handle to identify an open file. Such
descriptors are used in library functions or system calls such as read() and
write() to perform I/O operations.
2. In Unix/Linux, each process has by default three open file descriptors:
a. Standard input (file descriptor 0, i.e. read(0,buf, 4) reads 4 characters from the
standard input to the buffer buf). Typically, the standard input for a program
launched from the command line is the keyboard input.
b. Standard output (file descriptor 1).
c. Standard error (file descriptor 2).
d. When a command is run from the shell, the standard input, standard output
and standard error are connected to the shell tty (terminal). So reading the
standard input reads from the keyboard and writing to the standard output or
standard error writes to the display.
e. Note that many library functions used these file descriptors by default. For
example printf(“String”) writes “String” to the standard output.
f. From the shell it is possible to connect the standard output from one process to
the standard output to another process using the pipe character “|”. For
example, the command “who | wc” connects the standard output from the who
process to the standard input of the wc process such that any data written to
the standard output by the who process is written (via a pipe) to the standard
input of the wc process.
3. You will need the following C library functions:
a. fork() – should be familiar from lectures
b. pthread_create() – should be familiar from lectures
c. pipe()
• should be familiar from lectures
• note that multiple process can be attached to each end of the pipes,
which means that a pipe is maintained until no processes are
connected at either end of the pipe
d. execvp(const char * program, const char *args[]) (or execlp)
• replaces the current process with the program from the file specified in
the first argument
• the second argument is a NULL terminated array of strings
representing the command line arguments
• by convention, args[0] is the file name of the file to be executed
e. execlp(const char * program, const char *arg1, const char *arg2, … NULL)
• replaces the current process with the program from the file specified in
the first argument
• the second argument subsequent arguments are strings representing the
command line arguments.
• by convention, arg1 is the file name of the file to be executed
f. dup2(int newfd, int oldfd) – duplicates the oldfd by the newfd and closes the
oldfd. See for more
information. For example, the following program:
int main(int argc, char *argv[]) {
int fd;
printf(“Hello, world!”)
fd = open(“outFile.dat”, “w”);
if (fd != -1) dup2(fd, 1);
printf(“Hello, world!”);
will redirect the standard output of the program into the file outFile.dat, i.e.
the first “Hello, world!” will go into the console, the second into the file