Deadlocksituationer

Deadlocksituationer describe a state in which two or more processes or actors are blocked because each holds a resource the others require, so none can proceed. The term is used mainly in computer science but applies to other domains such as traffic and manufacturing.

Four conditions are commonly cited as necessary for a deadlock: mutual exclusion (resources are non-shareable), hold and wait (processes currently hold at least one resource while waiting for others), no preemption (resources cannot be forcibly taken from a process), and circular wait (a closed chain of processes each waiting for the next resource).

Examples: In computing, two processes each hold a lock on separate data and wait for the other's lock; in databases, two transactions wait for locks held by the other; in traffic, vehicles at a gridlocked intersection block each other.

Prevention and resolution: Prevention eliminates at least one condition, e.g., by requiring that all resources be requested at once, imposing a resource acquisition order, or preempting resources. Avoidance uses knowledge about future requests, e.g., the Banker's algorithm. Detection involves monitoring resource graphs and identifying wait-for cycles; resolution often means aborting one or more processes or rolling back transactions.

Related concepts include livelock, starvation, and resource allocation graphs.