Write a note on deadlocks.

The proper definition of deadlock

A set of processes is deadlocked if every process in the set is waiting for an event that only a process in the set can cause.

There are four essential conditions for deadlock to occur. They are as follows:

1. Mutual Exclusion: Resources are not sharable.
2. Non-preemption: formerly a resource is given to a process it can't be revoked until the process voluntarily gives it up.
3. Hold and Wait: It is probable for a process that is holding resources to request more.
4. Circular wait: It is probable for there to be a cyclic pattern of requests.

The techniques used by OS for handling deadlock are:

1. Deadlock detection and recovery: Permit the system to enter a deadlock state, detect it and then recover.

1. Deadlock prevention: Use a protocol to make sure that the system will never enter a dead lock state.          

      3.   Deadlock avoidance: Evade deadlock by careful resource scheduling.