race condition

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race condition

[′rās kən‚dish·ən]
(electricity)
An ambiguous condition occurring in control counters when one flip-flop changes to its next state before a second one has had sufficient time to latch.

race condition

Anomalous behavior due to unexpected critical dependence on the relative timing of events.

For example, if one process writes to a file while another is reading from the same location then the data read may be the old contents, the new contents or some mixture of the two depending on the relative timing of the read and write operations.

A common remedy in this kind of race condition is file locking; a more cumbersome remedy is to reorganize the system such that a certain processes (running a daemon or the like) is the only process that has access to the file, and all other processes that need to access the data in that file do so only via interprocess communication with that one process.

As an example of a more subtle kind of race condition, consider a distributed chat network like IRC, where a user is granted channel-operator privileges in any channel he starts. If two users on different servers, on different ends of the same network, try to start the same-named channel at the same time, each user's respective server will grant channel-operator privileges to each user, since neither will yet have received the other's signal that that channel has been started.

In this case of a race condition, the "shared resource" is the conception of the state of the network (what channels exist, as well as what users started them and therefore have what privileges), which each server is free to change as long as it signals the other servers on the network about the changes so that they can update their conception of the state of the network. However, the latency across the network makes possible the kind of race condition described. In this case, heading off race conditions by imposing a form of control over access to the shared resource -- say, appointing one server to be in charge of who holds what privileges -- would mean turning the distributed network into a centralized one (at least for that one part of the network operation). Where this is not acceptable, the more pragmatic solution is to have the system recognize when a race condition has occurred and to repair the ill effects.

Race conditions also affect electronic circuits where the value output by a logic gate depends on the exact timing of two or more input signals. For example, consider a two input AND gate fed with a logic signal X on input A and its negation, NOT X, on input B. In theory, the output (X AND NOT X) should never be high. However, if changes in the value of X take longer to propagate to input B than to input A then when X changes from false to true, there will be a brief period during which both inputs are true, and so the gate's output will also be true. If this output is fed to an edge-sensitive component such as a counter or flip-flop then the temporary effect ("glitch") will become permanent.

race condition

An error condition in which two signals or sets of data collide. It can take place within a chip, a circuit, a network or an application. It can be due to a timing malfunction in the hardware or poorly written software.
References in periodicals archive ?
FAVOURED by the race conditions, Meri Devie should be tough to beat in the Grade 3 Irish Independent Hurdle in Limerick.
SynthOS automatically ties them all together in a single real-time system that meets timing requirements, avoids hazards like deadlocks and race conditions, and is hardened against security breaches from mal-ware.
The Warwick contest has attracted 14 entries but four trainers were caught out by the race conditions, entering horses who have won in the past year.
Making the most of the excellent race conditions, Slovona, a 24-year-old sport and tourism student at the University of Almaty, dominated the 1.
TABLE 1 Means and Standard Deviations of Positive and Negative Affect Schedule-Expanded Form Subscale Scores for Race and No-Race Conditions Race Condition (n = 145) Pretest Posttest M SD M SD Fear 1.
Vettel edged Hamilton in the second 90-minute practice session at the Yas Marina track that replicated race conditions as it began under a setting sun and ended in darkness.
Another test under race conditions is planned at the fourth VLN round on 28 May.
Constantly changing with the times and adapting race conditions, Aintree should instead just get ahead of the game.
He hasn't had his optimum race conditions for a while and he should get them there.
Couple that wind with cool temperatures in the low 50s and race conditions were causing runners to salivate.
Four miles holds no fears for him whatsoever, nor particularly would heavy ground and I think the race conditions, 0-150, actually suit him pretty well.
Because of her lack of recent success and due to her age, the three-year-old is well treated by the race conditions which has no doubt prompted her shrewd trainer to take up this entry.