![]() ![]() However, if a deadlock occurs we can reboot our system and the deadlock is resolved automatically. Operating systems such as UNIX and Windows follow this approach. Since the problem of deadlock situation is not frequent, some systems simply ignore it. In the method, the system assumes that deadlock never occurs. Resource Preemption: Resources are taken one by one from a process and assigned to higher priority processes until the deadlock is resolved.Abort one process at a time until the system recovers from the deadlock.We let the system fall into a deadlock and if it happens, we detect it using a detection algorithm and try to recover. If the system enters into an unsafe state, it has to take a step back to avoid deadlock. Therefore, it requires additional information such as how many resources of each type is required by a process. If allocating that resource sends the system into an unsafe state, the request is not granted. When a process requests a resource, the deadlock avoidance algorithm examines the resource-allocation state. ![]() Since deadlock occurs when all the above four conditions are met, we try to prevent any one of them, thus preventing a deadlock. This is done by restraining the ways a request can be made. The first two methods are used to ensure the system never enters a deadlock. Methods of Handling Deadlocks in Operating System Therefore, all four conditions are satisfied. None of the two processes releases their resources before their execution and this creates a circular wait. Each process is holding a resource and waiting for the other process the release the resource it requires. Since the resources are non-shareable they can only be used by one process at a time(Mutual Exclusion). This creates a situation of deadlock because none of the two processes can be executed. Process 1 holds "Resource 1" and needs "Resource 2" while Process 2 holds "Resource 2" and requires "Resource 1". In the above figure, there are two processes and two resources. This creates a circular relation between all these processes and they have to wait forever to be executed. For example, lets say there are a set of processes such that P 0 P_0 P 0 depends on P 1 P_1 P 1 , P 1 P_1 P 1 depends on P 2 P_2 P 2 , P 2 P_2 P 2 depends on P 3 P_3 P 3 and P 3 P_3 P 3 depends on P 0 P_0 P 0 .
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