Question

1. When a process executes a "sleep" system call, from the perspective of the process, it simply pauses for a specified amount of time and then resumes where it left off. Describe, in detail, what a sleep system call looks like from the perspective of the operating system.
2. Regarding system calls:
   1. What is a system call?
   2. For each of the following system calls, give a condition that would cause it to fail: 1) open; 2) fork; and 3) exec.

Answer 1

The sleep system call consists of specified number of seconds , It's syntax is as given below :

 unsigned int sleep(unsigned int seconds);

When a sleep() call is encountered the thread which is called sleeps for the given number of seconds or it is interrupted by another signal . The return value of the sleep() is zero or the remaining number of seconds on interruption of it by another signal.

a) The interaction between a process and operating system is done by using a system call . The users can obtain services from the operating system using a system call .

b) 1) The open() system call can cause failure if the file mentioned is not available .

2) When fork() fails a negative integer is returned , if there is no enough memory on kernel to perform the task fork() fails

3) If there are errors specified for library functions exec() will fail , for example for error [E2BIG] the system call execve() will fail