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semaphore    
n. 臂式号志,信号,手旗信号
vt. 以信号机联络
vi. 打信号

臂式号志,信号,手旗信号以信号机联络打信号

semaphore
信号; 信号标志; 信号灯

semaphore
旗号

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

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

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 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 = s1;
}

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)


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  • single. dvi - University of Wisconsin–Madison
    A semaphore is an object with an integer value that we can manipulate with two routines; in the POSIX standard, these routines are sem wait() and sem post()1 Because the initial value of the semaphore deter-mines its behavior, before calling any other routine to interact with the semaphore, we must first initialize it to some value, as the
  • CONCURRENCY: SEMAPHORES - University of Wisconsin–Madison
    AGENDA LEARNING OUTCOMES Concurrency abstractions How can semaphores help with producer-consumer? How to implement semaphores?
  • CS 537 Notes, Section #10: Semaphore Implementation
    Test and set is tricky to use, since you cannot get at it from HLLs Typically, use a routine written in assembler, or an HLL pragma Using test and set to implement semaphores: For each semaphore, keep a test-and-set integer in addition to the semaphore integer and the queue of waiting processes
  • CONCURRENCY: SEMAPHORES, DEADLOCK
    Build Semaphore from Lock and CV Typedef struct { int value; cond_t cond; lock_t lock; Semaphores } sem_t; Locks
  • CS 537 Notes, Section #6: Semaphores and Producer Consumer Problem
    P (semaphore): an atomic operation that waits for semaphore to become positive, then decrements it by 1 Called sem_wait in pthreads (which we'll use on Linux) V (semaphore): an atomic operation that increments semaphore by 1 Called sem_post in pthreads The names come from the Dutch, proberen (test) and verhogen (increment) Semaphores are simple and elegant and allow the solution of many
  • CS 537 Notes, Section #7: Semaphore Example: Readers and Writers
    Semaphore usage generally falls into two classes: Uniform resource usage, simple first-in-first-out scheduling: use semaphores for everything This is usually the case Use one semaphore for each constraint in the system More complex patterns of resource usage: interaction between different users of a resource, or changing priorities: semaphores cannot capture the scheduling all by themselves
  • Microsoft Word - 31-40. doc
    wait if value of semaphore s is negative } int sem_post(sem_t *s) { increment the value of semaphore s by one if there are one or more threads waiting, wake one }
  • CS 537 Notes, Section #12: Deadlock
    Deadlock is one area where there is a strong theory, but it is almost completely ignored in practice Reason: solutions are expensive and or require predicting the future
  • UW Computer Sciences User Pages
    semaphore to ensure that only a single writer can acquire the lock and thus enter the critical section to update the data structure in question More interesting is the rwlock_acquire_readlock() and rwlock_release_readlock() pair When acquiring a read lock, the reader first acquires "lock" and then increments the "readers" variable to track





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