ch.8 deadlock

Question 1

what is a deadlock?

Answer 1

occurs when two or more threads are waiting for an event that can only be caused by another process

Question 1

what is a preemptable resource?

Answer 1

can be taken away from a process without a problem

Question 2

what is a preemptable resource?

Answer 2

would cause a problem to fail if taken away

Question 3

starvation

Answer 3

an indefinite block of a thread
- all deadlocks cause starvation
- not all starvation are caused by deadlocks

Question 4

what are the four conditions for deadlock?

Answer 4

1. mutual exclusion, each resource is held at most by one process
2. hold and wait: a process holding resources can request more resources
3. no preemption : the system cannot take resources from a process
4. circular wait: there is a circular chain of 2 or more process where each is waiting for a resource held by the next member of the chain

Question 5

what is live lock?

Answer 5

occurs when threads can execute but cannot make progress

Question 6

how do we deal with deadlock?

Answer 6

1. prevent mutual exclusion: Ensure that resources don’t need to be held to be used.
   Ex: queue print jobs instead of holding a printer
2. prevent hold and wait : require processes to request all necessary processes
3. Design all resources to be preemptable. This is kinda how
   databases work: all transactions can be aborted.
4. prevent circular wait : Always acquire resources in same order. This is the “systems”
   way