Using shared memory . . . with no safe guards.

In this assignment you will write a program that connects to a shared
memory segment that contains two integers. The first integer is a
numerical value that corresponds to a number of cows in a stable. Your
process has come to this shared memory to take a cow from that
stable. The second integer is going to be a unique id. When you take a
cow, you leave your own id so that the next person knows it is their
turn to take a cow. This id (and who you follow) will be assigned to
you during class.


Your program will connect to the shared memory.  Your program should
report to the console the initial value and the initial unique id
stored in the shared memory space. Then your program should wait until
the initial id matches the users id that precedes you. If the id's do
not match, your program will sleep for 1 second, wake up and then try
again. You can use the usleep function in unistd.h for this. When the
id does finally match, you reduce the number of cows by 1 and then
change the id to your own. If this deduction results in a negative
value for cows, set the cows to 999,999,999 instead. Your program
should then report to the console the new cows value and unique id of
the shared memory space and it may safely exit.



When finished, detach from the shared memory segment but do not remove
it.

Your data structure could look like this:

struct data {
   int cows;
   int id;
};


To make sure that we all connect to the shared memory segment for this
assignment, use ftok("/bin/ls",'A') to get the key.  In addition, pass
only 0777 as the last argument to shmget as the shared memory is
already created and the other flags are both unnecessary and
problematic in that situation.


IDs: (You'll need to know yours and your "previous")


Adam		497     (use previous as 1471)
Daniel		804
Jacquelyn	207
Ashley		560
Henning		322
Caleb		1351
Alex		1589
Georgios	1433
Erin		917
Tianyi		1471