Operating Systems: Fork, Pipe, and Memory Allocation

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Questions and Answers

What is the primary purpose of the fork() system call?

To execute a new program.

To create a new child process. (correct)

To suspend the parent process.

To terminate a running process.

What value does fork() return to indicate that the creation of a child process was unsuccessful?

A positive value.

An error code.

Zero.

A negative value. (correct)

Which of the following statements about the child process created by fork() is correct?

It shares the same process ID as the parent process.

It runs with a different program counter than the parent process.

It cannot communicate with the parent process.

It has the same open files that were being used in the parent process. (correct)

What does the child process receive as a return value from fork()?

Zero. Signup and view all the answers

In which environment does the fork() system call NOT compile?

Windows environment. Signup and view all the answers

What is the main function of a pipe in the context of process communication?

To connect standard output of one process to standard input of another. Signup and view all the answers

What happens if a process attempts to read from a pipe before any data has been written to it?

The reading process is suspended until data is available. Signup and view all the answers

Which function is responsible for creating a pipe in UNIX operating systems?

pipe() Signup and view all the answers

What is the primary purpose of the malloc() function in C?

To allocate a single large block of memory Signup and view all the answers

Which function would you use to allocate memory for an array of 10 integers initialized to zero?

calloc() Signup and view all the answers

What will be the return value of the malloc() function if the memory allocation request fails?

NULL Signup and view all the answers

Which function is used to deallocate memory that has been previously allocated?

free() Signup and view all the answers

What is the key difference between malloc() and calloc()?

calloc() initializes memory with zeros, while malloc() does not initialize Signup and view all the answers

What does the realloc() function do?

It re-allocates memory preserving existing values. Signup and view all the answers

When using the free() function, which statement is true?

It must be called for memory allocated with malloc() and calloc(). Signup and view all the answers

What happens to newly allocated blocks of memory when using realloc()?

They contain default garbage values. Signup and view all the answers

Study Notes

Fork() System Call

Creates a copy of the calling process - the child process
Both parent and child process execute the next instruction following the fork() call
Child process inherits the parent process's program counter, CPU registers, and open files
Returns an integer value:
- Negative Value: unsuccessful child process creation
- Zero: returned to the newly created child process
- Positive Value: returned to the parent process, containing the child process's ID (PID)
Not supported in Windows environments

Pipe

Acts as a connection between two processes, where the output of one becomes the input of the other
Enables one-way communication - one process writes to the pipe, the other reads
Accessible by both the creating process and its children for reading and writing
If a process tries to read from an empty pipe, it is suspended until data is written

Dynamic Memory Allocation

C library functions: malloc(), calloc(), free(), realloc()
These functions facilitate dynamic memory allocation in C programming

`malloc()`

Allocates a single, contiguous block of memory with the specified size
Returns a void pointer, which can be cast to any type
Doesn't initialize memory, leaving it with default garbage values
Function Signature:
- void *malloc(size_t size)
- size: memory size in bytes
- Returns a pointer to the allocated memory or NULL if the request fails

`calloc()`

Allocates a specified number of blocks with a specific type
Similar to malloc(), but initializes each block with the default value (0)
Requires two parameters: number of elements (n) and the size of each element (element-size)
Function Signature:
- ptr = (cast-type*)calloc(n, element-size);

`free()`

Used to de-allocate memory previously allocated with malloc() or calloc()
Prevents memory leaks by freeing unused memory
Function Signature:
- free(ptr);

`realloc()`

Dynamically adjusts the size of previously allocated memory
Maintains existing values and initializes new blocks with default garbage values
Function Signature:
- ptr = realloc(ptr, newSize);
- newSize: the new desired memory size

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Description

This quiz covers critical concepts in operating systems, focusing on the fork() system call, pipe communication, and dynamic memory allocation. Test your understanding of how processes interact and manage memory resources in a programming environment. Perfect for students studying operating systems in computer science courses.