Deadlocks
    - Deadlocks can occur on hardware resources or on software resources.

Necessary conditions for a deadlock:

A dead lock situation can arise if the following conditions hold simultaneously in a system:

• Mutual Exclusion - some resources must be used/ held in a non-sharable manner.  A resource can be held by no more than one process at a time.

• Hold and wait - process that is holding a resource and is waiting to acquire additional resources that are currently being held by other processes.  Processes do not voluntarily release resources until finished.

• No preemption - Resources cannot be preempted.   Resource is only released by holding process.  We don't take resources away from processes once they've been assigned.

• Circular wait - A process wait on resources held by another waiting process.  e.g. P₁ waiting for R₁ which is held by P₂ which is waiting for R₂ held by P₁.