Prob #$57$ in book:

Write a shell script in C$++$ that produces a file of sequential numbers by reading the last number in the file, adding $1$ to it$,$ and then appending it

to the file. Run one instance of the script in the background and one in the foreground, each accessing the same file.$($Hint: run a

command ending in a & to run in the background$)--$ Assume integer numbers.

How long does it take before a race condition manifests itself? What is the critical region? Modify the script to prevent the ace.

$($Hint: use

In file file.lock

to lock the data file. Or$,$ you can use the official way "flock".$)$