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Exercise Sheet 3

Note that starting with this exercise all implementation work should be completed in C. Ensure that your programs compile with -Wall -Werror.

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

Hint: Remember that a process can be created with fork(), vfork(), and in Linux also with clone(). A parent process can wait for its children using wait() or waitpid(). Choose the most suitable option for process creation and waiting for every situation.

Task 1

a)

Write a program in which the parent process creates exactly 7 child processes and waits for them to finish. Every child process finishes immediately after being created.

b)

Write a program which creates exactly 12 child processes. After that, the parent process prints on the standard output the message: 12 child processes have been created.

Every child process simply prints its pid on the standard output. Analyse the obtained output. Is the order of the messages (parent and child ones) consistent? Can the order of these messages be predicted? What does it depend on?

Task 2

Write a program in which the parent creates exactly 1 child process. The child process should print its pid to the standard output and then finish. The parent process waits until it is sure that the child has terminated. The parent terminates after it has waited for the child process.

Note that you may not use wait() or waitpid() in this task.

Hint: Check the man page of fork() to see whether a parent is notified of child termination via any signal. Also see sigaction() to determine how to respond to an incoming signal.

Task 3

Write a program in which the parent process creates exactly 1 child. After creating the child, the behaviour of the parent process is as follows: Five seconds after creating the child, the parent process sends SIGUSR2 to the child. Afterwards it continously sends SIGUSR1 every five seconds until the child process has terminated. To implement this behaviour the parent process must use the following functions: alarm() and pause().

The behaviour of the child is as follows: On startup, it first blocks SIGUSR2, and unblocks it after 13 seconds. Upon receiving a signal the child should react as follows:

  • SIGUSR1 prints a message to standard out.
  • SIGUSR2 terminates the process.

Hint: Check the man page of alarm(), pause(), sigprocmask() and sigaction(). For a general overview see man 7 signal.