Deadlock

Question 1

Name and explain the two types of correctness properties for concurrent programs

Answer 1

Safety properties - property must always be true e.g. acquire semaphore for access to critical section
Liveness properties - must eventually become true

Question 2

what are the four conditions that must be satisfied simultaneously for deadlock to occur?

Answer 2

Mutual excl
Hold and wait
No preemption - resource can only be released voluntarily by the threads
circular wait - think circular dependencies

Question 3

Why can we not remove mutual exclusion (as a condition for deadlock)

Answer 3

Safety is a requirement

Question 4

why can we not remove hold and wait (as a condition for deadlock)

Answer 4

impractical, low resource utilization, starvation possible

Question 5

Why can we not remove preemption (as a condition for deadlock)

Answer 5

impractical for most systems - performance issues, primitives are atomic and cannot be interrupted