Deadlock Definition
A set of processes is deadlocked if each process in the set is waiting for an event that only another process in the set can cause (including itself).
Waiting for an event could be:
waiting for access to a critical section
waiting for a resource Note that it is usually a non-preemptable (resource). pre-emptable resources can be yanked away and given to another.
It could also be a situation in which two computer programs sharing the same resource are effectively preventing each other from accessing the resource, resulting in both programs ceasing to function.
Conditions for Deadlock
Mutual exclusion: resources cannot be shared.
Hold and wait: processes request resources incrementally, and hold on to what they've got.
No pre-emption: resources cannot be forcibly taken from processes.
Circular wait: circular chain of waiting, in which each process is waiting for a resource held by the next process in the chain.
Strategies for dealing with Deadlock
ignore the problem altogether ie. ostrich algorithm it may occur very infrequently, cost of detection/prevention etc may not be worth it.
detection and recovery
avoidance by careful resource allocation
prevention by structurally negating one of the four necessary conditions.
Re: What is a deadlock ?
Deadlock Definition
A set of processes is deadlocked if each process in the set is waiting for an event that only another process in the set can cause (including itself).
Waiting for an event could be:
waiting for access to a critical section
waiting for a resource Note that it is usually a non-preemptable (resource). pre-emptable resources can be yanked away and given to another.
It could also be a situation in which two computer programs sharing the same resource are effectively preventing each other from accessing the resource, resulting in both programs ceasing to function.
Conditions for Deadlock
Mutual exclusion: resources cannot be shared.
Hold and wait: processes request resources incrementally, and hold on to what they've got.
No pre-emption: resources cannot be forcibly taken from processes.
Circular wait: circular chain of waiting, in which each process is waiting for a resource held by the next process in the chain.
Strategies for dealing with Deadlock
ignore the problem altogether ie. ostrich algorithm it may occur very infrequently, cost of detection/prevention etc may not be worth it.
detection and recovery
avoidance by careful resource allocation
prevention by structurally negating one of the four necessary conditions.