What is it?
In Multi-threading applications or Distributed Computing systems, a lock is used when multiple threads try to access the same resource at the same time. One thread will lose and will need to wait the other to finish, so it can use the resource.
A lock is also a mechanism which some programming languages such as Java use to explicitly control access to a shared resource. Applying locks provides exclusive access to a single thread, and every other need for the lock to be acquired by it first.
Below, a Mutual Exclusion of a shared resource and two threads:
