Locking
To make a file or other piece of data inaccessible. File locking is a critical
component of all multi-user computer systems, including local area networks.
When users share files, the operating system must ensure that two or more users
do not attempt to simultaneously modify the same file. The operating system
prevents simultaneous write operations by locking the file as soon as the first
user opens it. All subsequent users may read the file, but they cannot write to
it until the first user releases the file.