NOTES.txt

COMPILING

   For compilation we provided a shell script ('compile.sh') that you can run and it will
   compile everything. This way you don't need to give each executable permission to be 
   run, although you will need to give 'compile.sh' permission to run.


EXECUTING

   For running the program just run the DB_editor executable in a terminal. In an effort
   to make our program easy to use, our DB_server, interest and write_state processes
   are all child processes of the DB_editor so you don't need to worry about them. After
   this you can run as many ATM's as you want in separate terminals.


EXAMPLE COMPILING AND EXECUTING COMMANDS
	
In one terminal:
	$ chmod +x compile.sh
	$ ./compile.sh
	$ ./DB_editor

Then one terminal for each ATM:
	$ ./ATM


EXITING
   
   For exiting the program the simplest way is to just type 'X' when prompted to choose an
   operation in the DB_editor. This will delete all IPCs and exit all processes including the
   ATMs. We did it this way to make it easy to use and because we considered the DB_editor to
   be sort of like an administrator user, while the ATMs are just regular users. Each ATM can 
   be exited individually by typing 'X' when asked for an account number and then closing the 
   terminal window.

   If you accidentally exit the DB_editor by closing the terminal window, the ATM's will not 
   be terminated and you will not delete the IPCs properly. To fix this, you can just run the
   DB_editor again and type 'X' to exit right away. The IPCs will be properly deleted.


OTHER IMPORTANT NOTES

   There is an interesting side effect that happens occasionally that when DB_server checks 
   all other user input, the DB_editor may cause a segmentation fault if you input an invalid 
   value when first prompted to choose an operation. If you do this occurs, you will need to 
   do ps aux and kill the child processes of the DB_editor manually to terminate the program.

   The way we protected accounts was using an array of binary semaphores. In order to
   do this we need to be able to set the array to a fixed length. We thought it was
   outside of the scope of the project to use a linked list for this because it would
   be much more complicated. With the array implementation there is a limit to the number
   of accounts that can exist at one time. Currently, the max number of accounts is 10, 
   but this can be changed by changing the 'NUM_LOCKS' constant in 'structs.h'.

   If you close an ATM manually you will get a sem_acquire failed message because of the
   way we made it so that the DB_editor can close the ATM. This is done by having each ATM
   fork itself to have a parent process that waits for the DB_editor to tell it to close,
   and a child process that does all of the ATM work. This way, when the ATM tells the
   parent to close, the actual ATM will be also forced to close. The sem_acquire failure
   message is not a problem at all.