Concurrency Manager

The advent of web–based information systems significantly increased the number of concurrent programs. Concurrent programs must control concurrency to guarantee safe implementations, which avoid interference that lead systems to inconsistent states and behaviors. To implement some of these controls we need to use programming language features, such as blocking methods to avoid their concurrent execution in the same object. In the Java [6] programming language we can do this synchronizing methods with the synchronized method modifier, which forbid concurrent execution of methods within an object. However, implementation of such features brings performance overhead, serializing the execution of some operations. There are several approaches concerned about guaranteeing performance increasing, removing unnecessary synchronization of Java concurrent programs [3, 1, 5]. They show the negative impact in efficiency of the Java concurrency control mechanisms. This negative impact demands alternatives to increase programs’ performance. Method synchronization guarantees that all concurrent execution of a method within an object will be serialized. With this approach we can allow or block all concurrent execution of a method. However, if some execution flows cannot be concurrently executed, but others can, we need an intermediary approach.