A set of processes is deadlocked if each process in the set 
is waiting for an event that only another process in the 
set can cause (including itself). 
To avoid these r the stratagies to be followed

 
Attacking Mutex condition 
Attacking preemption 
Attacking hold and wait condition 
Attacking circular wait

Deadlock is permanent blocking of the set processes that 
either compete for system resources or communicate each 
other.
we can avoid deadlock by avoiding the following conditions:
1.Mutual Exclusion
2.Hold and wait.
3.No preemption.
4.circular wait.