any website is fine
2006-12-23 01:18:32 · 6 answers · asked by norah S. 1 in Computers & Internet ➔ Programming & Design
A semaphore is a protected variable (or abstract data type) and constitutes the classic method for restricting access to shared resources (e.g. storage) in a multiprogramming environment. They were invented by Edsger Dijkstra and first used in the THE operating system.
The value of the semaphore is initialized to the number of equivalent shared resources it is implemented to control. In the special case where there is a single equivalent shared resource, the semaphore is called a binary semaphore. The general case semaphore is often called a counting semaphore.
2006-12-23 01:20:07 · answer #1 · answered by R2 3 · 0⤊ 0⤋
The semaphore or optical telegraph is an apparatus for conveying information by means of visual signals, with towers with pivoting blades or paddles, shutters, in a matrix, or hand-held flags etc. Information is encoded by the position of the mechanical elements; it is read when the blade or flag is in a fixed position. In modern usage it refers to a system of signaling using two handheld flags.
Other forms of optical telegraphy include ship flags, Aldis lamps, and Heliographs.
Semaphore lines preceded the electrical telegraph.
They were faster than post riders for bringing a message over long distances, but far more expensive and less private than the electrical telegraph lines which would replace them.
The distance that an optical telegraph can bridge is limited by geography and weather, thus in practical use, most optical telegraphs used lines of relay stations to bridge longer distances.
2006-12-23 09:19:44 · answer #2 · answered by Anonymous · 0⤊ 0⤋
type semaphore on the search for questions here in yahoo answers. you'll find several links there..
2006-12-23 09:21:25 · answer #3 · answered by rjyll 2 · 0⤊ 0⤋
See wikipedia (2 meanings).
2006-12-23 09:21:24 · answer #4 · answered by ricochet 5 · 0⤊ 0⤋
For trains: http://www.semaphores.com/
For flag signalling: http://www.anbg.gov.au/flags/semaphore.html
For computers: http://java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/Semaphore.html
Sometimes search engines like Ask.com or Google.com or even Yahoo.com are quicker at finding answers than waiting for others to do the work for you.
2006-12-23 09:33:48 · answer #5 · answered by sparkletina 6 · 0⤊ 0⤋
how about www.google.com
2006-12-23 09:20:41 · answer #6 · answered by free_indeed2000 4 · 0⤊ 0⤋