(deadlocks)

In concurrent computing, deadlock is any situation in which no member of some group of entities can proceed because each waits for another member, including itself, to take action, such as sending a message or, more commonly, releasing a lock. Deadlocks are a common problem in multiprocessing systems, parallel computing, and distributed systems, because in these contexts systems often use software or hardware locks to arbitrate shared resources and implement process synchronization.

<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}. [Jargon File] (2000-07-26)

deadlock

<parallel> /li:v'lok/ When two or more processes continuously change their state in response to changes in the other process(es) without doing any useful work. This is similar to deadlock in that no progress is made but differs in that neither process is blocked or waiting for anything. A human example of livelock would be two people who meet face-to-face in a corridor and each moves aside to let the other pass, but they end up swaying from side to side without making any progress because they always move the same way at the same time. [Jargon File] (1998-07-05)

In game theory, Deadlock is a game where the action that is mutually most beneficial is also dominant. This provides a contrast to the Prisoner's Dilemma where the mutually most beneficial action is dominated.