In its simplest form, deadlock occurs when each of two (minimun two) threads try to acquire a lock on a resource already locked by another.

E.g:
Take example of two threads
1. thread 1
2. Thread 2
And two resources
1. Resource 1
2. Resource 2
Thread 1 locked on Resources 1 and tries to acquire a lock on Reosurce 2.
At the same time, Thread 2 has a lock on Resource 2 and it tries to acquire lock on Resource 1.
Two threads never give up their locks, hence a DEADLOCK occures.

 Solution :
The simplest way to avoid deadlock is to use a timeout value .
You can use the Monitor class (system.Threading.Monitor) to set a timeout during acquiring a lock.

Ex. in C#
if(Monitor.TryEnter(this, 500))
{
// critical section
}
catch (Exceprion ex)
{
}
finally
{
Monitor.Exit();
}

 
Here the timeout is 500 milliseconds .
If the lock can’t be acquired, after 500 miliseconds, timeout occurs and the code exit the Monitor block.