Deadlock

A deadlock is a situation wherein two or more competing actions are waiting for the other to finish, so neither ever does. It is often seen in a paradox, like the chicken or the egg.

Deadlock avoidance

Deadlock can be avoided if certain information about processes is available in advance of resource allocation. For every resource request, the system sees if granting the request will mean that the system will enter an unsafe state, meaning a state that could result in deadlock. The system then only grants request that will lead to safe states. In order for the system to be able to figure out whether the next state will be safe or unsafe, it must know in advance at any time the number and type of all resources in existence, available, and requested. One known algorithm that is used for deadlock avoidance is the Banker's algorithm. However, for many systems it is impossible to know in advance what every process will request. This means that deadlock avoidance is often impossible.

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