Anomalou
s behavior due to unexpected critical dependence on the relative timing of event
s. For example, if one proce
ss write
s to a file while another i
s reading from the
same location then the data read may be the old content
s, the new content
s or
some mixture of the two depending on the relative timing of the read and write operation
s. A common remedy in thi
s kind of race condition i
s {file locking} a more cumber
some remedy i
s to reorganize the
sy
stem
such that a certain proce
sse
s (running a
daemon or the like) i
s the only proce
ss that ha
s acce
ss to the file, and all other proce
sse
s that need to acce
ss the data in that file do
so only via interproce
ss communication with that one proce
ss. A
s an example of a more
subtle kind of race condition, con
sider a
distributed chat network like
IRC, where a
user i
s granted channel-operator
privileges in any channel he
start
s. If two u
ser
s on different
servers, on different end
s of the
same network, try to
start the
same-named channel at the
same time, each u
ser'
s re
spective
server will grant channel-operator privilege
s to each u
ser,
since neither will yet have received the other'
s signal that that channel ha
s been
started. In thi
s ca
se of a race condition, the "
shared re
source" i
s the conception of the
state of the network (what channel
s exi
st, a
s well a
s what u
ser
s started them and therefore have what privilege
s), which each
server i
s free to change a
s long a
s it
signal
s the other
server
s on the network about the change
s so that they can update their conception of the
state of the network. However, the
latency acro
ss the network make
s po
ssible the kind of race condition de
scribed. In thi
s ca
se, heading off race condition
s by impo
sing a form of control over acce
ss to the
shared re
source --
say, appointing one
server to be in charge of who hold
s what privilege
s -- would mean turning the di
stributed network into a centralized one (at lea
st for that one part of the network operation). Where thi
s i
s not acceptable, the more pragmatic
solution i
s to have the
sy
stem recognize when a race condition ha
s occurred and to repair the ill effect
s. Race condition
s al
so affect electronic circuit
s where the value output by a
logic gate depend
s on the exact timing of two or more input
signal
s. For example, con
sider a two input AND gate fed with a logic
signal X on input A and it
s negation, NOT X, on input B. In theory, the output (X AND NOT X)
should never be high. However, if change
s in the value of X take longer to propagate to input B than to input A then when X change
s from fal
se to true, there will be a brief period during which both input
s are true, and
so the gate'
s output will al
so be true. If thi
s output i
s fed to an edge-
sen
sitive component
such a
s a counter or flip-flop then the temporary effect ("
glitch") will become permanent. (2002-08-03)
style="border-width:thin; border-color:#333333; border-style:dashed; padding:5px;" align="left">In addition suitable contents:
[ 2 ] [ = ] [ accept ] [ ad ] [ ae ] [ af ] [ ag ] [ ai ] [ al ] [ am ] [ an ] [ AND ] [ app ] [ ar ] [ arc ] [ arg ] [ as ] [ at ] [ av ] [ B ] [ b ] [ be ] [ bo ] [ bot ] [ br ] [ bt ] [ by ] [ C ] [ ca ] [ case ] [ cat ] [ cc ] [ ch ] [ channel ] [ char ] [ ci ] [ circuit ] [ ck ] [ co ] [ com ] [ component ] [ con ] [ cons ] [ control ] [ cr ] [ cu ] [ cy ] [ D ] [ daemon ] [ data ] [ date ] [ de ] [ diff ] [ ding ] [ do ] [ du ] [ ec ] [ ed ] [ ee ] [ eg ] [ eh ] [ electron ] [ er ] [ era ] [ es ] [ et ] [ event ] [ expect ] [ fi ] [ file ] [ flip-flop ] [ fo ] [ for ] [ fr ] [ free ] [ ga ] [ gate ] [ ge ] [ gh ] [ gi ] [ gl ] [ glitch ] [ gm ] [ gn ] [ gr ] [ h ] [ hang ] [ hat ] [ hr ] [ id ] [ ie ] [ iff ] [ il ] [ in ] [ inc ] [ input ] [ int ] [ io ] [ IR ] [ ir ] [ IRC ] [ is ] [ it ] [ ke ] [ ki ] [ la ] [ latency ] [ ld ] [ Lex ] [ li ] [ location ] [ logic gate ] [ ls ] [ lu ] [ ly ] [ ma ] [ man ] [ mm ] [ mo ] [ mod ] [ module ] [ mp ] [ mu ] [ N ] [ na ] [ named ] [ nc ] [ ND ] [ ne ] [ net ] [ network ] [ ng ] [ ni ] [ nl ] [ nn ] [ no ] [ NOT ] [ np ] [ ns ] [ O ] [ om ] [ op ] [ operator ] [ org ] [ OT ] [ output ] [ pa ] [ pe ] [ ph ] [ pl ] [ point ] [ pr ] [ pragma ] [ process ] [ pt ] [ query ] [ rc ] [ re ] [ ro ] [ ru ] [ run ] [ sa ] [ sam ] [ say ] [ sc ] [ se ] [ serve ] [ server ] [ servers ] [ sh ] [ shar ] [ si ] [ sig ] [ signal ] [ sit ] [ so ] [ solution ] [ source ] [ spec ] [ st ] [ state ] [ su ] [ sy ] [ system ] [ T ] [ table ] [ tar ] [ tc ] [ th ] [ theory ] [ to ] [ tp ] [ tr ] [ tron ] [ tw ] [ um ] [ up ] [ us ] [ user ] [ va ] [ value ] [ ve ] [ vi ] [ while ] [ write ] [ X ] [ ye ]