ETYM Greek sema a sign + pherein to bear: cf. French sémaphore.
An apparatus for visual signaling with lights or mechanically moving arms.
In programming, a signal—a flag variable—used to govern access to shared system resources. A semaphore indicates to other potential users that a file or other resource is in use and prevents access by more than one user.
A semaphore is nothing more than a variable that is protected.
It provides a means to restrict access to a resource that is shared amongst two or more processes. Two operations are permitted, commonly called acquire and release.
1. To convey by semaphore, of information.
2. To send signals by or as if by semaphore.
Visual signaling code in which the relative positions of two moveable pointers or hand-held flags stand for different letters or numbers. The system is used by ships at sea and for railroad signals.