Lec1- Introduction for OS Deadlock

Deadlock

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Deadlock can be defined as the permanent blocking of a set of processes that either compete for system resources or communicate with each other.A set of processes is deadlocked when each process in the set is blocked awaiting an event (typically the freeing up of some requested resource) that can only be triggered by another blocked process in the set. Deadlock is permanent because none of the events is ever triggered. Unlike other problems in concurrent process management, there is no efficient solution in the general case. All deadlocks involve conflicting needs for resources by two or more processes. A common example is the traffic deadlock. Figure 6.1a shows a situation in which four cars have arrived at a four-way stop intersection at approximately the same time.The four quadrants of the intersection are the resources over which control is needed.In particular,if all four cars wish to go straight through the intersection,the resource requirements are as follows: