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11 Cards in this Set
- Front
- Back
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conditions for deadlock
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1. mutual exclusion
2. hold-and-wait 3. no preemption 4. circular wait |
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what is mutual exclusion?
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only one process may use a resource at a time
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what is hold-and-wait?
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process holds resource while waiting for another
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what is preemption / what is no preemption?
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no preemption: can't take a resource away from a process
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what is circular wait?
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waiting processes form a cycle
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ways to attack deadlock problem?
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- deadlock prevention
- deadlock avoidance - deadlock detection |
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what is deadlock prevention?
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make deadlock impossible by removing a condition
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what is deadlock avoidance?
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avoid getting into situations that lead to deadlock
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what is deadlock detection?
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- don't try to stop deadlocks
- instead, if they happen, detect and resolve |
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how do you prevent deadlock?
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simply prevent any single condition for deadlock
1. mutual exclusion - make all resources sharable 2. hold-and-wait - get all resources simultaneously (wait until all free) AND only request resources when it has none 3. no preemption - allow resources to be taken away (at any time) 4. circular wait - order all resources, force ordered acquisition |
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how do you avoid deadlock?
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- avoid situations that lead to deadlock. selective prevention: remove condition only when deadlock a possibility
- works with incremental resource requests: resources are asked for in increments, do not grant request that can lead to a deadlock - requires knowledge of maximum resource requirements |
