Java Multithreading & Concurrency Overview

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Multithreading and Concurrency in Java-
Java was one of the first languages to make multithreading easily available to developers. Java had multithreading capabilities from the very beginning. Therefore, Java developers often face the problems described above. That is the reason I am writing this trail on Java concurrency. As notes to myself, and any fellow Java developer whom may benefit from it.

The trail will primarily be concerned with multithreading in Java, but some of the problems occurring in multithreading are similar to problems occurring in multitasking and in distributed systems. References to multitasking and distributed systems may therefore occur in this trail too. Hence the word "concurrency" rather than "multithreading".

Concurrency Models-

The first Java concurrency model assumed that multiple threads executing within the same application would also share objects. This type of concurrency model is typically referred to as a "shared state concurrency model". A lot of the concurrency language constructs and utilities are designed to support this concurrency model.

However, a lot has happened in the world of concurrent architecture and design since the first Java concurrency books were written, and even since the Java 5 concurrency utilities were released

The shared state concurrency model causes a lot of concurrency problems which can be hard to solve elegantly. Therefore, an alternative concurrency model referred to as "shared nothing" or "separate state" has gained popularity. In the separate state concurrency model the threads do not share any objects or data. This avoids a lot of the concurrent access problems of the shared state concurrency model.

New, asynchronous "separate state" platforms and toolkits like Netty, Vert.x and Play / Akka and Qbit have emerged. New non-blocking concurrency algorithms have been published, and new non-blocking tools like the LMax Disrupter have been added to our toolkits. New functional programming parallelism has been introduced with the Fork and Join framework in Java 7, and the collection streams API in Java 8.