Deadlock avoidance methods analyze resource allocation to determine if granting a request would lead to an unsafe state where deadlock could occur. A deadlock happens when multiple processes are waiting indefinitely for resources held by each other in a cyclic dependency. To prevent deadlock, an operating system must have information on current resource availability and allocations, as well as future resource needs. The system only grants requests that will lead to a safe state where there are enough resources for all remaining processes and deadlock is not possible.

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Deadlock Avoidance in Operating System

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  PRESENTATION ONDEADLOCK AVOIDANCE
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  In this slidewe are going toknow:What is Deadlock?How can we Avoid Deadlock?
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  What is Deadlock?Adeadlock is a situation which occurs when a process enters in a waiting statebecause the requested resource is being held by another waiting process, which inturn is waiting for another resource held by another waiting process. If a process isunable to change its state indefinitely because the resources requested by it arebeing used by another waiting process, then the system is said to be in a deadlock.
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  A practical exampleof Deadlock You can't get a job without experience. You can't get experience without a job.Let’s visualize DeadlockTwo processes competing for two resources in opposite order.(A) A single process goes through.(B) The later process has to wait.(C) A deadlock occurs when the first process locks the first resource at thesame time as the second process locks the second resource.(D) The deadlock can be resolved by cancelling and restarting the firstprocess.
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  Deadlock Avoidance Deadlockcan be avoided if certain information about processesare available to the operating system before allocation of resources. For every resource request, the system sees whether granting therequest will cause the system to enter an unsafe state that meansthis state could result in deadlock.The system then only grants the requests that will lead to safestates.
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  Possible States Deadlock:No further progress is possible. Unsafe State: A state that may allow deadlock. It is possible for aprocess to be in an unsafe state but for this not to result in adeadlock. Safe State: A state is safe if it has a bunch of processes and thereare enough resources for the 1st process to be finished and after itreleases it’s resources there are enough resources for the nextprocess to be proceed. There is no chance of Deadlock.
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  In order todetermine the condition of next state (safe/ unsafe/ deadlock) thesystem must know these information in advance: Resources currently available. Resources currently allocated to each process. Resources that will be required and released by these processes in the future.To avoid deadlock we have to follow a simple rule. If a request causes the nextstate into unsafe mood or deadlock then we shouldn’t proceed the request.THE END
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  Presented by:Mohammad Hafiz-Al-Masud,ID:1209035,Session: 2012/13,Department of ICT,Comilla University.