semaphore

from WordNet (r) 3.0 (2006)

semaphore
    n 1: an apparatus for visual signaling with lights or
         mechanically moving arms
    v 1: send signals by or as if by semaphore
    2: convey by semaphore, of information

from The Collaborative International Dictionary of English v.0.48

Semaphore \Sem"a*phore\, n. [Gr. sh^ma a sign + fe`rein to bear:
   cf. F. s['e]maphore.]
   A signal telegraph; an apparatus for giving signals by the
   disposition of lanterns, flags, oscillating arms, etc.
   [1913 Webster] Semaphoric

from The Free On-line Dictionary of Computing (8 July 2008)

semaphore

   <programming, operating system> The classic method for
   restricting access to shared resources (e.g. storage) in a
   {multi-processing} environment.  They were invented by
   {Dijkstra} and first used in {T.H.E} {operating system}.

   A semaphore is a {protected variable} (or {abstract data
   type}) which can only be accessed using the following
   operations:

   	P(s)
   	Semaphore s;
   	{
   	  while (s == 0) ;	/* wait until s>0 */
   	  s = s-1;
   	}

   	V(s)
   	Semaphore s;
   	{
   	  s = s+1;
   	}

   	Init(s, v)
   	Semaphore s;
   	Int v;
   	{
   	  s = v;
   	}

   P and V stand for Dutch "Proberen", to test, and "Verhogen",
   to increment.  The value of a semaphore is the number of units
   of the resource which are free (if there is only one resource
   a "binary semaphore" with values 0 or 1 is used).  The P
   operation {busy-waits} (or maybe {sleeps}) until a resource is
   available whereupon it immediately claims one.  V is the
   inverse, it simply makes a resource available again after the
   process has finished using it.  Init is only used to
   initialise the semaphore before any requests are made.  The P
   and V operations must be {indivisible}, i.e. no other process
   can access the semaphore during the their execution.

   To avoid {busy-wait}ing, a semaphore may have an associated
   {queue} of processes (usually a {FIFO}).  If a process does a
   P on a semaphore which is zero the process is added to the
   semaphore's queue.  When another process increments the
   semaphore by doing a V and there are tasks on the queue, one
   is taken off and resumed.

   (1995-02-01)

from Moby Thesaurus II by Grady Ward, 1.0

72 Moby Thesaurus words for "semaphore":
      Roman candle, aid to navigation, alarm, amber light, balefire,
      beacon, beacon fire, bell, bell buoy, blinker, blue peter, buoy,
      caution light, flare, fog bell, fog signal, fog whistle, foghorn,
      glance, go light, gong buoy, green light, heliograph, high sign,
      international alphabet flag, international numeral pennant, kick,
      leer, marker beacon, nod, nudge, parachute flare, pilot flag, poke,
      police whistle, quarantine flag, radio beacon, red flag, red light,
      rocket, sailing aid, semaphore flag, semaphore telegraph, sign,
      signal, signal beacon, signal bell, signal fire, signal flag,
      signal gong, signal gun, signal lamp, signal light, signal mast,
      signal post, signal rocket, signal shot, signal siren,
      signal tower, spar buoy, stop light, the nod, the wink, touch,
      traffic light, traffic signal, watch fire, white flag, wigwag,
      wigwag flag, wink, yellow flag