What is a Safe State and its’ use in deadlock avoidance?

When a process requests an available resource, system must decide if immediate allocation leaves the system in a  safe state

v  System is in safe state if there exists a safe sequence of all processes.  

v  Sequence <P1, P2… Pn> is safe if for each Pi, the resources that Pi can still request can be satisfied by currently available resources + resources held by all the Pj, with j<I.

     If Pi resource needs are not immediately available, then Pi can wait until all Pj have finished.

     When Pj is finished, Pi can obtain needed resources, execute, return allocated resources, and terminate. 

     When Pi terminates, Pi+1 can obtain its needed resources, and so on. 

Deadlock Avoidance ⇒ ensure that a system will never enter an unsafe state.