How to deal with deadlock ?

There are three possible approaches to dealing with deadlock:

• Deadlock prevention — Deadlock can be prevented by ensuring that at least one of the four conditions required for deadlock never occurs. For example, by using sharable resources, never holding one resource while waiting for another, making resources preemptible, or by imposing a strict logical ordering on resource allocation requests so that all threads request resources in the same order.

• Deadlock avoidance — If more information on the pattern of resource usage is known, then it is possible to construct an algorithm that will allow all the four conditions necessary for deadlock to occur, but which will also ensure that the system never enters a deadlock state. A deadlock avoidance algorithm will examine dynamically the resource allocation state and take action to ensure that the system can never enter into deadlock. Any resource allocation request that is potentially unsafe is denied.

• Deadlock detection and recovery — In many general-purpose concurrent systems, the resource allocation usage is a priori unknown. Even if it is known, the cost of deadlock avoidance is often prohibitive. Consequently, many of these systems will ignore the problems of deadlock until they enter a deadlock state. They then take some corrective action (for example, by aborting a concurrent activity and preempting its resources.)