exercise02

Exercise Sheet 2

In this exercise sheet you will work with processes and signals.

Remember to provide a Makefile, and to adhere to our general guidelines for programming exercises.

Task 1

Write a program which creates N child processes, where N can be specified on the command line.

Every child

• Computes the 40th number of the Fibonacci sequence.
• Prints a message of the form "Child <i> PID = <PID>. Fib(40) = <fib(40)>" where PID refers to the process id.

The parent waits until all children have exited and then prints "Done".

You may use the following implementation for the Fibonacci sequence:

unsigned fib(unsigned n) {
  if(n <= 1) return n;
  return fib(n - 1) + fib(n - 2);
}

Example output:

./task1 2
Child 0 PID = 19698. Fib(40) = 102334155
Child 1 PID = 19699. Fib(40) = 102334155
Done

Analyze the obtained output. Is the order of the messages consistent? Can the order of these messages be predicted? What does it depend on?

Hint: Remember that a child process can be created with fork(). A parent process can wait for its children using wait() or waitpid()

Task 2

Write a program in which the parent creates a single child process. The child process prints the message "Child <PID> sleeping for 5 seconds..." and then sleeps for five seconds, using the sleep() function. Afterwards it prints "Child done" and exits. The parent process waits until it is sure that the child has terminated, prints "Parent done" and exits as well. There is a catch, however: In this task, you must not use wait() or waitpid().

Example output:

./task2
Child 20196 sleeping for 5 seconds...
Child done
Parent done

Hint: Check the man page of fork() to see whether the parent is somehow notified of child termination. Also see sigaction() to determine how to respond to an incoming signal. For a general overview on signals see man 7 signal.

Task 3

Write a program in which the parent process creates a single child process.

The parent

• Waits three seconds and then sends SIGUSR2, followed by SIGUSR1 to the child
• It then continuously sends SIGUSR1 every three seconds, until the child process has terminated
• Finally, it prints "Parent done" and exits

To implement this behavior the parent process must use the following functions: alarm() and pause() (or alternatively sigsuspend()). You must not use sleep().

The child

• Blocks SIGUSR2 for 13 seconds
• Upon receiving SIGUSR1, it prints "Received SIGUSR1"
• Upon receiving SIGUSR2, it prints "Child done" and exits

Note that you may use sleep() in the child process.

Example output:

./task3
Received SIGUSR1
Received SIGUSR1
Received SIGUSR1
Received SIGUSR1
Child done
Parent done

Hint: Check the man page of alarm(), pause(), kill(), sigprocmask() and sigaction().