semaphores

Noun

semaphore (countable and uncountable, plural semaphores)

1. Any equipment used for visual signalling by means of flags, lights, or mechanically moving arms, which are used to represent letters of the alphabet, or words.
   • We must here take the liberty of expostulating with Sir Home [Riggs] Popham and the first Lord of the Admiralty, for having given to the telegraphic machine, invented by that gallant officer, the barbarous name of Semaphore, instead of Sematophore or Semophore—either of them ugly enough.[1820 January, “Art. II.—Thesaurus Græcæ Linguæ ab H. Stephano [Henry Stephens] constructus. Editio nova, auctior et emendatior. Vol. I. Partes I–IV. Londini, in ædibus Valpianis, 1815–1818. [book...
2. A visual system for transmitting information using the above equipment; especially, by means of two flags held one in each hand, using an alphabetic and numeric code based on the position of the signaller's arms; flag semaphore.
   • Its [the article's] object is to furnish a rule for determining the number of distinct signals which can be made by any semaphore, whatever be the number of arms or indicators, of whatever be the number of positions of each arm. In the Cyclopædia of Rees, the number of signals which the semaphores...1834 October, Charles Blackburn, “XXXV. A Method of Determining the Number of Signals which Can be Made by the Modern Telegraphs.”, in David Brewster, Richard Taylor, Richard Phillips, editors, The...
3. A bit, token, fragment of code, or some other mechanism which is used to restrict access to a shared function or device to a single process at a time, or to synchronize and coordinate events in different processes.
   • The thread increments the semaphore to prevent other threads from entering the critical section at the same time.

See all 4 meanings of semaphore