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13 Cards in this Set
- Front
- Back
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deadlock |
When a process is stuck in waiting state because the resources it has requested are held by other waiting processes. The process never finishes executing |
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The four simultaneous conditions of a deadlock |
Mutual exclusion. |
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Mutual exclusion |
At lease one resource must be held in a nonsharable mode; only one process at a time can use a resource. If another process requests that resource, the requesting process must be delayed until the resource has been released. |
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Hold and wait |
A process must be holding at least one resource and waiting to acquire additional resources that are currently being held by other processes. |
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No preemption |
Resources cannot be preempted. A resources can be released only voluntarily by the process holding it, after that process has completed its task. |
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Circular wait |
A set of waiting processes must exist such that the first process is waiting for a resource held by the next process which is waiting for a resources held by the next and so on and so forth until the last process is waiting for a resource held by the very first process. |
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system resources- allocation graph |
This graph consists of a set of vertices V and a set of edges E. The set of vertices is partitioned into two different types of nodes P (set of active processes in the system) and R (set of all resource types in the system). |
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requested edge |
A directed edge Pi -> Rj. |
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assignment edge |
A directed edge Rj -> Pi. |
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Deadlock prevention |
provides a set of methods to ensure that at least on of the necessary conditions cannot hold. Prevent deadlocks by constraining how requests for resources can be made. |
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Deadlock avoidance |
requires that the operating system be given additional information in advance concerning which resources a process will request and use during its lifetime. |
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Safe state |
If the system can allocate resources to each process (up to its maximum) in some order and still avoid deadlock. Only exists if there is a safe sequence. |
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modify (dirty) bit |
reduces the overhead of page transfers - only modified pages are written to disk. |
