LU5 IPC

Question 1

What does IPC stand for in system programming?

Answer 1

Interprocess Communication

Question 2

What is the primary purpose of IPC?

Answer 2

To allow two or more processes to exchange information with each other.

Question 3

Name two types of IPC mechanisms that only support local usage.

Answer 3

Signals & pipes

Question 4

What happens if the buffer in a pipe is empty?

Answer 4

The reader process will be suspended.

Question 5

What happens if the buffer in a pipe is full?

Answer 5

The writer process will be suspended.

Question 6

What is the purpose of the pipe ‘|’ symbol in Linux?

Answer 6

It tells the shell to create a pipe, connecting the output of one process to the input of another.

Question 7

What is the difference between unnamed and named pipes?

Answer 7

Unnamed pipes:

• are temporary and used by related processes

Named pipes (FIFOs):

• are permanent and can be used by unrelated processes.

Question 8

What system call is used to create an unnamed pipe?

Answer 8

pipe()

Question 9

What are the two file descriptors returned by the pipe() system call?

Answer 9

• reading (p[0])
• writing (p[1])

Question 10

What happens if a process tries to write to a full pipe?

Answer 10

The writer process will be suspended until there is space in the pipe.

Question 11

What happens if a process tries to read from an empty pipe?

Answer 11

The reader process will be suspended until data is available in the pipe.

Question 12

What is the default behavior of pipes regarding data flow?

Answer 12

Pipes treat data on a first-in-first-out (FIFO) basis.

Question 13

What is the minimum size of an unnamed pipe in most systems?

Answer 13

512 bytes
(depends)

Question 14

What system call is used to create a named pipe (FIFO)?

Answer 14

mkfifo() or mknod()

Question 15

What is the advantage of using named pipes over unnamed pipes?

Answer 15

Named pipes can be used by unrelated processes and have a larger buffer capacity.

Question 16

What is the purpose of the fcntl() function in non-blocking I/O?

Answer 16

To set the O_NONBLOCK flag, which prevents blocking when reading from or writing to a pipe.

Question 17

What does the O_NONBLOCK flag do when set on a pipe?

Answer 17

It makes read and write operations non-blocking, returning immediately even if the pipe is empty or full.

Question 18

What is the purpose of the fstat() function in IPC?

Answer 18

To obtain file’s metadata when have an open file descriptor.

To get the number of characters in the pipe using the st_size member of the stat structure.

Question 19

What is the main drawback of unnamed pipes?

Answer 19

They cannot be used by unrelated processes and are temporary.

Question 20

What is the typical buffer capacity of a named pipe (FIFO)?

Answer 20

Around 40K bytes

Question 21

What is the purpose of the wait() system call in IPC?

Answer 21

To avoid zombie processes by waiting for child processes to terminate.

Question 22

What is the difference between a unidirectional and bidirectional pipe?

Answer 22

unidirectional pipe:

*allows data flow in one direction

bidirectional pipe:

*allows data flow in both directions.

Question 23

What is the purpose of the close() system call in IPC?

Answer 23

To close file descriptors associated with a pipe when they are no longer needed.

Question 24

What is the purpose of the fork() system call in IPC?

Answer 24

To create a child process that can communicate with the parent process using pipes

Question 25

What is the purpose of the exec() system call in IPC?

Answer 25

To replace the current process image with a new process image, often used in conjunction with fork().

Question 26

What is the purpose of the mknod command in UNIX?

Answer 26

To create special files, including named pipes (FIFOs).

Question 27

What is the purpose of the mkfifo() system call?

Answer 27

To create a named pipe (FIFO) with a specified pathname and access permissions.

Question 28

What is the purpose of the O_NONBLOCK flag in the open() system call?

Answer 28

To prevent blocking when opening a FIFO for reading or writing.

Question 29

What is the purpose of the `perror()` function in IPC?

Answer 29

To print an error message to `stderr`(fd=2) based on the current value of `errno`.

Question 30

What is the purpose of the exit() function in IPC?

Answer 30

To terminate a process and return a status code to the parent process.

Question 31

What is the purpose of the `read()` system call in IPC?

Answer 31

To read data from a **pipe** or **file descriptor**.

Question 32

What is the purpose of the write() system call in IPC?

Answer 32

To write data to a pipe or file descriptor.

Question 33

how to check if a child is created successfully using fork()?

Answer 33

return 0

Question 34

What is the purpose of the wait(NULL) system call in IPC examples?

Answer 34

To make the parent process wait for the child process to terminate.

Question 35

What is the purpose of the close(p[0]) call in IPC examples?

Answer 35

To close the read end of the pipe in the child process.

Question 36

What is the purpose of the close(p[1]) call in IPC examples?

Answer 36

To close the write end of the pipe in the parent process.

Question 37

What is the purpose of the exit(1) call in IPC examples?

Answer 37

To terminate the process with a status code of 1 if an error occurs.

Question 38

What is the purpose of the exit(0) call in IPC examples?

Answer 38

To terminate the process with a status code of 0, indicating success.

Question 39

What is the purpose of the printf() function in IPC examples?

Answer 39

To print the contents of the buffer read from the pipe.

Question 40

What is the purpose of the char inbuf[MSGSIZE] declaration in IPC examples?

Answer 40

To declare a buffer for storing data read from the pipe.

Question 41

What is the purpose of the int p[2] declaration in IPC examples?

Answer 41

To declare an array to hold the file descriptors for the pipe.

Question 42

What is the purpose of the pid_t pid declaration in IPC examples?

Answer 42

To declare a variable to hold the process ID returned by fork().

Question 43

What is the purpose of the wait system call in IPC?

Answer 43

To make the parent process wait for the child process to terminate.

Question 44

What is the purpose of the O_RDONLY flag in the open() system call?

Answer 44

To open a file or FIFO for reading only.

Question 45

What is the purpose of the O_WRONLY flag in the open() system call?

Answer 45

To open a file or FIFO for writing only.

Question 46

What is the purpose of the O_RDWR flag in the open() system call?

Answer 46

To open a file or FIFO for both reading and writing.

Question 47

What is the purpose of the O_CREAT flag in the open() system call?

Answer 47

To create a file or FIFO if it does not already exist.

Question 48

What is the purpose of the O_TRUNC flag in the open() system call?

Answer 48

To truncate a file to zero length if it already exists.

Question 49

What is the purpose of the O_APPEND flag in the open() system call?

Answer 49

To append data to the end of a file instead of overwriting it.

Question 50

What is the purpose of the O_EXCL flag in the open() system call?

Answer 50

To ensure that a file or FIFO is created exclusively, failing if it already exists.

Question 51

What is the purpose of the O_NONBLOCK flag in the open() system call?

Answer 51

To make the open operation non-blocking, returning immediately even if the file or FIFO is not ready.