Question

How do the semantics of the fork() change for multithreaded processes vs single processes?

Answer 1

fork() system call:

The fork() system call is used to create a new process(child process) that will be executed concurrently with the parent process. This system call returns an integer value and this value may be of three types:

1. Zero
2. Positive
3. Negative

1. Zero

The zero value is returned to the newly created child process.

2. Positive value

The positive value is returned to the parent process and this value is the process id of the child process.

3. Negative value

The negative value is returned if the child process is not created successfully.

In the multithreaded system when a fork() system call is called then a new program is created with the same code.

A thread process is considered a sibling of the existing process while a forked process is considered a child process.  

vfork() System Call:

vfork() system call is similar to fork() system call but does not create an identical copy of the parent process.

The syntax of vfork() is given below:

pid_t vfork(void);