Eventloop Module

Eventloop module is the foundation of other modules that run their code inside event loops and threads. It provides efficient management of asynchronous operations without multithreading overhead. Particularly useful for building client-server applications with high performance requirements.

You can add Eventloop module to your project by inserting dependency in pom.xml:


  • Eventloop utilizes Java’s NIO to allow asynchronous computations and I/O operations (TCP, UDP).
  • Eliminates traditional bottleneck of I/O for further business logic processing.
  • Can run multiple eventloop threads on available cores.
  • Minimal GC pressure: arrays and byte buffers are reused.
  • Eventloop can schedule/delay certain tasks for later execution or background execution.
  • Eventloop is single-threaded, so it doesn’t have concurrency overhead.

Eventloop represents an infinite loop, where each loop executes all the tasks that are provided by Selector or stored in special queues. Each of these tasks should be small and its execution is called tick.

The only blocking operation of Eventloop infinite loop is Selector.select(). This operation selects a set of keys whose corresponding channels are ready for I/O operations. With these keys and queues with tasks, it begins asynchronous executing in one thread in the overridden method run() (Eventloop is an implementation of Runnable).

Eventloop works with different types of tasks that are stored in separate queues:

Tasks Description
Local tasks Tasks which were added from current Eventloop thread
Concurrent tasks Tasks which were added from other threads
Scheduled tasks Tasks which are scheduled to be executed later
Background tasks Same as Scheduled, but if there are only Background tasks left, Eventloop will be closed

Execution of an eventloop will be ended when its queues with non-background tasks are empty, Selector has no selected keys and amount of concurrent operations in other threads equals 0. To prevent Eventloop closing in such cases, you should use keepAlive flag (when set true, Eventloop will continue running even without tasks).

You can explore Eventloop examples here

This module on GitHub repository