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deadlock

[′ded‚läk]
(computer science)
A situation in which a task in a multiprogramming system cannot proceed because it is waiting for an event that will never occur. Also known as deadly embrace; interlock; knot.

deadlock

1. A lock equipped with a dead bolt only.
2. A lock in which a bolt is moved by means of a key or thumb turn, and is positively stopped in its projected position.

deadlock

(parallel, programming)
A situation where two or more processes are unable to proceed because each is waiting for one of the others to do something.

A common example is a program waiting for output from a server while the server is waiting for more input from the controlling program before outputting anything. It is reported that this particular flavour of deadlock is sometimes called a "starvation deadlock", though the term "starvation" is more properly used for situations where a program can never run simply because it never gets high enough priority.

Another common flavour is "constipation", in which each process is trying to send stuff to the other but all buffers are full because nobody is reading anything). See deadly embrace.

Another example, common in database programming, is two processes that are sharing some resource (e.g. read access to a table) but then both decide to wait for exclusive (e.g. write) access.

The term "deadly embrace" is mostly synonymous, though usually used only when exactly two processes are involved. This is the more popular term in Europe, while deadlock predominates in the United States.

Compare: livelock. See also safety property, liveness property.

deadly embrace

A stalemate that occurs when two elements in a process are each waiting for the other to respond. For example, in a network, if one user is working on file A and needs file B to continue, but another user is working on file B and needs file A to continue, each one waits for the other. Both are temporarily locked out. The software must be able to deal with this. Contrast with livelock.
References in periodicals archive ?
When told that the meeting between the dockworkers and the IOCs was deadlocked, jatto said, 'am not aware of that because what I know is that the strike has not taken a full effect on port operations but rather a skeletal area at the quay.
Once the algorithm terminates the execution, it declares all the nodes that have not been reduced in the set [UC.sub.init] as deadlocked.
But with multilateral negotiations deadlocked, regionalism could easily reinforce rather than contain protectionist forces, as it did in the 1930s.
The WTO global trade negotiations under the current Doha Round have been deadlocked since the collapse of a ministerial meeting in Mexico last September.
''Relations between Iraq and the (U.N.) Security Council are in effect deadlocked now,'' Iraq's Deputy Prime Minister and acting Foreign Minister Tareq Aziz told reporters.
When a jury "cannot reach a verdict by the required voting margin," a hung, or deadlocked, jury results.(3)
Bush and Al Gore were deadlocked in the tightest-ever race for the office of President of the United States.
According to the merger agreement between Telenor and Telia the two companies are supposed to seek arbitration in a Danish court after an issue has been deadlocked for 30 days.
A detection mechanism identifies potential deadlock configurations; once deadlock is detected, a recovery scheme breaks the deadlocked cycle.
The hypercube in Figure 1(b) is in a deadlocked state, since no message can completely reserve the path to its destination in order to complete its transmission and release the links it has reserved.
Regarding the other patent, the jury found noninfringement on one of the two claims and the judge declared the jury deadlocked on the remaining claim.