Java Concurrency Uncovered — Part 4: Why new Thread() Doesn't Scale

Understanding the limitations of manual thread management and why Java moved toward task-based concurrency

In the previous articles, we explored the fundamentals of Java multithreading using three core primitives: Thread, Runnable, and synchronized. For simple, small-scale applications, these building blocks are often sufficient. However, as applications grow and handle increasing levels of concurrency, the limitations of manually managing threads become difficult to ignore.

Creating a thread is easy. Managing thousands of threads efficiently is a different problem altogether.

In this article, we’ll explore why creating a new thread for every task doesn’t scale, what limitations Runnable and synchronized have in larger applications, and how Java 5 introduced the java.util.concurrent package to move concurrency toward a more task-oriented approach.

Threads Are Expensive to Create and Destroy

Creating a thread using new Thread() works well when there are only a few concurrent tasks. The problem starts when the number of tasks grows. If an application creates a new thread for every incoming request, the number of threads grows along…