Deadlock [110]

• finite number of resources distributed to competing processes

• physical: memory space, CPU cycles, I/O devices

• logical: files, semaphores

• multiple instances of a resource type

• process requests, uses, releases resource

• deadlock: set of procs waiting for release from one (or more) members of set

Deadlock: Necessary Conditions [110]

• mutual exclusion: at least one nonshareable resource

• hold and wait: at least one proc holds resource, waits for other

• no preemption: resources can only be voluntarily released

• circular wait: P0 waiting for P1 ... waiting for P0

• circular wait IMPLIES hold and wait

• if you can break any one of these conditions IMPLIES no deadlock