To complete the signals$-$based chat program described above, do the following. We recommend doing them in order. Each is described in more detail below.

Note the above instructions regarding testing on portal.

I would recommend working in pairs on this lab, but note that both instances of the chat program need to run as the same user. $($You can$$t send signals to another user$$s programs.$)$

Start with the template program below that prints out its PID and reads in another PID into a global variable.

As described below, the template program sets up access to two shared memory regions:

my$\_$inbox which is this process$$s inbox for chat messages;

other$\_$inbox which is the other process$$s inbox for chaat messages.

Your code will write to other$\_$inbox and read from my$\_$inbox.

Create a signal handler for the SIGINT, SIGTERM, and SIGUSR$1$ signals

SIGTERM should invoke cleanup$\_$inboxes and then exit

SIGINT should invoke cleanup$\_$inboxes and then send SIGTERM to the other user and then exit

SIGUSR$1$ should display the contents of the inbox $($eventually in shared memory; make a pointer to a placeholder character array for now$)$ and then set its first character to be $\text{'}\backslash 0\text{'}$

$($Although normally one should take care to only use signal$-$safe functions in your signal handlers, for this lab, we do not care if you follow this rule.$)$