System Software and Operating System MCQ - Deadlocks
A system is in a safe state only if there exists a safe sequence of processes P1, P2, P3, Pn where:
For each Pi, the resources that Pi can still request can be satisfied by the currently available resources plus the resources help by all Pj, j<i.
If a system is in safe state, there is no deadlock.
If the system is deadlocked, it is in an unsafe state.
If a system is in unsafe state, there is a possibility for a deadlock.
Avoidance: making sure the system will not enter an unsafe state.
For each Pi, the resources that Pi can still request can be satisfied by the currently available resources plus the resources help by all Pj, j<i.
If a system is in safe state, there is no deadlock.
If the system is deadlocked, it is in an unsafe state.
If a system is in unsafe state, there is a possibility for a deadlock.
Avoidance: making sure the system will not enter an unsafe state.
Two processes can never lead to deadlock as the peak time demand of 6 (3 + 3) tape drives can be satisfied. But 3 processes can lead to a deadlock if each hold 2 drives and then demand one more.
Using Banker's algorithm, one can show that one process has to acquire all its needed resources. This process, after completing its task, will release all its resources, thereby avoiding any possible deadlock.
Having 11 resources ensures that atleast 1 process will have no pending request. This process after using will release the resources and so deadlock can never occur.
