Deadlock Prevention

• At least 1 necessary condition does not hold– Mutual Exclusion: not required for sharable resources; must hold for non-sharable resources.– Hold-and-Wait: can not request new when
holding resources.
• Protocol 1: request all resources before it begins execution
• Protocol 2: request resources only when the process has none.
• Low resource utilization; starvation possible.– No Preemption: preempt resources from processes
• Protocol 1: If a request can not be satisfied then preempt all resources held and block
• Protocol 2: Preempt only if resources are needed by another running process
• Requires resource state to be easily restored– Circular Wait: Block any request that results in a cycle.
• Impose a total ordering of all resource types, and require that each process requests resources in an increasing order