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The OpenVMS DLM periodically checks for deadlock situations. In the example above, the second lock enqueue request of one of the processes would return with a deadlock status. It would then be up to this process to take action to resolve the deadlock—in this case by releasing the first lock it obtained.
(B) Deadlock occurs when both processes lock the resource simultaneously. (C) The deadlock can be resolved by breaking the symmetry of the locks. (D) The deadlock can be prevented by breaking the symmetry of the locking mechanism. Deadlock prevention works by preventing one of the four Coffman conditions from occurring.
The UNIX and Windows operating systems take this approach. [ 1 ] [ 2 ] Although using the ostrich algorithm is one of the methods of dealing with deadlocks , other effective methods exist such as dynamic avoidance, banker's algorithm , detection and recovery, and prevention.
Banker's algorithm is a resource allocation and deadlock avoidance algorithm developed by Edsger Dijkstra that tests for safety by simulating the allocation of predetermined maximum possible amounts of all resources, and then makes an "s-state" check to test for possible deadlock conditions for all other pending activities, before deciding whether allocation should be allowed to continue.
Semaphore locking also has a time limit to prevent a deadlock condition in which a lock is acquired by a single process for an infinite time, stalling the other processes that need to use the shared resource protected by the critical section.
Upgrading a lock from read-mode to write-mode is prone to deadlocks, since whenever two threads holding reader locks both attempt to upgrade to writer locks, a deadlock is created that can only be broken by one of the threads releasing its reader lock. The deadlock can be avoided by allowing only one thread to acquire the lock in "read-mode ...
The problem which mutual exclusion addresses is a problem of resource sharing: how can a software system control multiple processes' access to a shared resource, when each process needs exclusive control of that resource while doing its work?
A simple solution to this problem is to add a waiter, who represents a lock, that the philosophers need exclusive access to before picking up either of their forks. Once a philosopher has exclusive access to the waiter’s attention they have that attention until the philosopher has successfully picked up both forks.