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deadlock prevention

·        Each process must request and acquire all the needed resources at the same time

·        Deny one of the required conditions for a deadlock

_ Cannot be done for non-sharable resources (like printers)

_ Sharable resources (read-only _les) do not require mutually exclusive access ) cannot be involved in deadlock

_ Cannot deny mutual exclusion as some resources are inherently non-sharable

_ Hold and Wait

_ Processes can request and acquire all the resources at one time

_ Request resources only if the process is holding none

If the process is holding any resources, they must be released before requests can be granted

 Disadvantages

1. Low resource utilization { resources may get allocated but not used for a long time

2. Possibility of starvation { on popular resources

_ No Preemption

_ If a process holding resources requests for another resource that cannot be immediately allocated, all currently held resources are

   preempted

_ Process restarted only when it regains all the resources

_ Suitable for resources whose state can be easily saved { CPU registers, memory

_ Circular Wait

_ Impose a total ordering on all resource types

_ Each process requests resources in an increasing order of enumeration

_ If several instances of a resource required, a single request must be issued for all of them

_ Deadlock Prevention based on Maximum Claims