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 Definitions for semaphore: 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
WordNet (r) 2.0
:
semaphore
n : 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
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
The Free On-line Dictionary of Computing (27 SEP 03)
:
semaphore
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-wait}s (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)
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