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in a multithreaded system, if the resource locked by one thread is needed by other and vice-versa, the system stops working. This is deadlock.

deadlock detection and avoidance is a problem in computer science, with many different approaches. these approaches would change with the system they are applied to.
a naive/beginner approach might be the logic that no thread/process should hold on to its resources if it can not find _all_ the resources it needs.

Check this out, its good:

cs.jhu.edu/~yairamir/cs418/os4/sld010.htm

Deadlock is a situation whereby two or more threads have locked resources needed by each other.
There are two schools of thoughts – Deadlock Prevention (a traffic light) and more promising, Deadlock Avoidance (a traffic police)

A deadlock occurs when a thread holds a resource and trying to acquire other resource already held by another thread,while that thread is also waiting for the first thread resource. Any number of threads can be involved in a deadlock if there is at least one resource per thread.Below are techniques to avoid deadlock:

1) Use sequence number with mutexes. Associate a sequence number with each mutex and acquire mutex in sequence. Never acquire a sequence number which is lower than sequence number already hold by thread.

2) Avoid locking more than one mutex at the same time.