Deadlock and Starvation

Deadlock and Starvation

Deadlock occurs when threads or processes cannot run because they are waiting for a resource that will never become available.

Starvation refers to a similar idea, but the thread or process may get to run a little, tiny bit, but is not able to actually complete its task.

Livelock occus when threads or processes can exeute, but are in a circular state, acquiring a resource, then releasing it, then acquiring it, then releasing it, ...
The "Hungry Philosophers" is a classic example used to describe deadlock.

So, here's the problem:

A bunch of philosophers (in this case 5 of them) are eating spaghetti. They also think a lot.

When they are thinking they do not eat. In order to eat, a philosopher must use both forks.

What algorithm will solve this problem and allow them to eat?

Another classic example is a husband and wife with one pen and one checkbook (and no ATM card). In order to write a check, they must have both the pen and the checkbook.

Note: Dealing with deadlock can be very complicated, and we won't necessarily be able to solve it.

However, in general, for production-level code, it is not sufficient to say that the odds of a particular deadlock situation are so low that it would be unlikely to occur.

Close is not good enough - you should guarantee deadlock can never happen.

Ok, time for another disclaimer, and in writing this time:
Multi-threaded, concurrent programming is a complicated and big topic. There are whole books on concurrent programming, and we could have an entire class on the subject. For this course, you should just get the basics and be able to use 2 or more threads in your programs as needed.
Liveness (Oracle Tutorials) - covers Deadlock, Starvation, and Livelock