Deadlock Flashcards
(12 cards)
Difference between deadlock prevention and deadlock avoidance
Deadlock prevention ensures atleast one of the conditions will never occur, whereas deadlock avoidance ensures the system will not enter a non safe state
Four conditions
Mutual exclusion
No pre-emption
Hold and wait
Circular wait
Mutual extension problem/solution
Resources are not shareable, only one process can user a resource at a time
Solution:
Share resources but some can’t be shared e.g. printer
No pre-emotion problem/solution
Only the process can release the resource
Solution: Use time quantum method - allocate time to each process to access the resources and once the time is up the resource will be released
Hold and wait problem/solution
Process is holding one resource and waiting for another
Solution: Try not to hold and wait - give processes the resources before it starts
Circular wait problem/solution
All processes are waiting for resources
Solution: Number the resources so that the process can request the resources in increasing order
What causes a deadlock
When two or more processes block each other by holding locks on resources that another process needs
Safe state
= no deadlock
The process allocated to the resource has completed successfully without problems
Unsafe state
= possibility of deadlock
Bankers Algorithm
Illustration
Why don’t Windows designers use deadlock avoidance and prevention
In modern o/s it’s almost impossible for a deadlock to occur because the os scheduler makes sure that all competing tasks gets a fair share of access to different resources
PCB
Process control block is the data structure maintained by the o/s which is indicated by the process ID. It keeps all the information needed to keep track of the process e.g.
- process ID (unique ID)
- process state (current state)
- process privileges (grants access to resources)
- pointer (points to parent process)
