When two or more threads of your program are blocked from 
gaining access to a resource and as a result cannot make 
ant progress, such a situation is called Starvation.

The ultimate form of Starvation is Deadlock. Deadlock 
occurs when two or more threads are waiting on a condition 
that cannot be satisfied. Most often a Deadlock occurs when 
two or more threads are each waiting for the other to do 
something.

Semaphores are used to avoid Deadlock situations.

Dead lock is the situation which occurs when a process is
waiting for a resource which is already handled by someother
process and that particular process is waiting for some
other resource to complete its task which is handled by some
other differnt process
it is cyclic