“Base to Bombardier”
 
Objectives
 
In this lab, each student is to prepare a single program called prog9.c which has a “base process” which communicates with child processes acting as “bombers” that it creates. The student specifically explores:
 
• Handling processes by use of fork(), getpid()and wait()
 
• Handling signals by use of signal(),alarm()and kill()
 
• Opening and accessing a console window buffer
 
Operation
 
Before executing the program, the user should open four console (terminal) windows.
The first terminal window will represent the base, and the other three will represent the three bombers.
 
The first action of the program’s main loop is to discover how many terminals are open by trying to open all possible terminal number buffers (e.g. /dev/pts/1,/dev/pts/1 etc…) as a read only file.
Those that are open should be stored so that the first four found can be written to.
 
The main function of the air base is use fork() to spawn three child bomber processes which are to execute the same exact code, and a fourth child (without an associated terminal window) to receive input and while monitoring and signaling the bombers.
 
Each bomber is to be initialized to contain 50 gallons of fuel, six bombs, and to be a distance of zero miles from the base. An alarm() timer is to be installed and used which:
 
• Decrements the fuel by two gallons each second.
 
• Increments the distance from base by one mile every two seconds if going toward target, and decrements the distance from base by one mile every two seconds if returning to base.
 
• Reports the fuel amount, ordinance left, and distance from base every three seconds in the appropriate terminal. e.g. Bomber id to base, g gallons left, b bombs left, m miles from base.

System Programming Concepts
 
If a bomber ever runs out of fuel it should be terminated by exiting with an unsuccessful code. If a bomber drops its entire payload, it should begin returning to base. If it makes it back to base without running out of fuel, it should terminate with a successfully code.
 
Input/output
 
The program should accept the following input (where invalid commands should produce a suitable error message):
 
• bn – Orders plane n (n = 1 to 3) to drop a bomb.
 
• rn – Refuels plane n’s fuel tank to 50 gallons.
 
• kn – Terminates (kills) the plane n process.
 
• q – Exits the program.
 
Given the bn command, the base should send the signal SIGUSR1 to plane n. Upon receiving the signal SIGUSR1, the plane should print out that it (plane n) has dropped a bomb and then print how many bombs it has left. When the plane has no more bombs left, it should print that it has no more ordinance left and that it is returning to base.
 
Given the rn command, the base process should send the signal SIGUSR2 to plane n. Upon receiving the signal SIGUSR2, a plane should refuel, resetting its fuel value to 50 gallons. Whenever a plane’s fuel drops below 5 gallons, it should print the message “Mayday, mayday!” If a plane uses all its fuel before being refueled, the plane should send the signal SIGUSR2 to the base, print the message “Bomber n down. Pick us up in the drink.” and then exit. The base should respond with “Vaya Con Dios, Flight n” in its terminal window.
 
Given the kn command, the base should terminate the selected child process and note such in its terminal. Given the q command, the base should terminate all child processes and close the program.