Common Multi-threading Mistakes in Java - Calling run() instead of start()

Common Multi-threading Mistakes in Java - Calling run() instead of start()

Writing multi-threaded and concurrent programs is not easy, not even in Java.  Even senior developers, including myself, make mistakes while writing concurrent Java applications. This is also one of the trickiest area of Java programming language, where misconceptions outnumbers concepts. Considering amount of misconception an average Java programmers has about multi-threading and concurrency, I thought to start a new series about common multi-threading mistakes done by Java programmers; what is better way to learn from common real word mistakes. Learning from mistakes has another name Experience, but if you only learn from your mistakes then there is only limited things you can learn, but if you learn from other peoples mistake, you can learn much more in short span of time. Have you ever thought, Why writing multi-threaded code is difficult? IMHO, primarily reason for this is that it multi-threading makes it hard for a code to speak for itself. Programmer read code sequentially to understand how it's executed, but it is only correct if one and only one thread is executing it. That's why Single threaded code are easy to read and debug. As soon as two threads comes into picture, It become very difficult to make prediction about how your code behave, especially in the absent of any synchronization rules e.g. rules enforced by Java Memory Model. Without JMM you can not make correct prediction about your code in a multi-threaded environment, because it's possible for one thread to stop at arbitrary point and another thread at different point. Situation becomes even more tricky if those threads are sharing data between them e.g. in form of objects, a poorly written multi-threaded program can cause deadlock, race condition and responsiveness issues, which will prevent a Java application to fulfil it's promise. I hope, in this series we can learn from each other's mistake and take a step forward on writing correct multi-threaded application in Java.