Concurrency

Its literal meaning is “happening at same time”. Whereas in context of object it’s the property that distinguishes an active object from the one that is not active. The object oriented programming focuses upon data abstraction, encapsulation and inheritance, concurrency focuses upon process abstraction ad synchronization. The object is a concept that unifies these two different viewpoints : each object (drawn from an abstraction of the real world) may represent a separate thread of control (a process abstraction). Such objects are called active . In a system based on an object-oriented design. We can conceptualize the world as consisting of a set of cooperative objects.some of which are active and thus serve as centers of independent activity. There are three approaches to concurrency in OOD:

• Concurrency as an intrinsic feature of certain programming languages.
• A language may use a class library that implements  concurrency
• Interrupts can be used to give illusion of concurrency, but it requires knowledge of certain low level hardware details

No matter which approach to concurrency we take one of the realities about concurrency is that once you introduce it into a systems. We must consider how active objects synchronize their activities with one another as well as with objects that are purely sequential. For example, if two active objects try to send messages to a third object, we must be certain to use some means of mutual exclusion, so that state of object being acted upon is not corrupted when both active objects try to update its state simultaneously. This is the point where the ideas of abstraction,encapsulation & concurrency interact.