Solving the Spring Boot Scheduled Task Continuation Problem During Shutdown

Discover how to prevent `Runnable` tasks from executing during server shutdown in `Spring Boot` applications using a custom `ThreadPoolTaskScheduler`.
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Solving the Spring Boot Scheduled Task Continuation Problem During Shutdown

When developing applications with Spring Boot, it’s common to implement scheduled tasks that perform routine operations like database maintenance or data cleanup. However, there may arise a situation where these scheduled tasks continue executing even after you send a shutdown request to the server. This behavior can lead to several exceptions and inconsistencies, particularly when the application context is shutting down and the underlying resources like the database are being closed.

In this guide, we will explore a common problem faced by developers when implementing scheduled tasks in Spring Boot, and we’ll provide a solution to ensure that these tasks stop executing during the server shutdown process.

Introduction to the Problem

As developers work on Spring Boot applications, they often utilize actuators for shutdown and restart functionalities. A user encountered issues where, despite a successful shutdown request (indicated by a 200 response), scheduled tasks continued execution. The logs revealed exceptions related to the EntityManager, indicating that once the application context starts shutting down, the resources needed for executing these tasks are no longer available.

Here are some key aspects of the issue:

Scheduled tasks continue running even when the server is shutting down.

Exceptions related to the EntityManager occur after shutdown, indicating attempts to access closed resources.

This problem not only leads to cluttered logs but may also affect the application’s integrity, especially concerning pending transactions or data operations.

Understanding the Solution

To resolve this issue, we can create a custom implementation of ThreadPoolTaskScheduler. The goal of this solution is to ensure that all scheduled tasks are cancelled before the shutdown process is fully executed.

Steps to Implement the Custom Scheduler

Create a Custom ThreadPoolTaskScheduler Implementation
We’ll extend the existing ThreadPoolTaskScheduler class, overriding the necessary methods to keep track of scheduled tasks and ensure proper cancellation during the shutdown procedure.

Here’s an example of the implementation:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code

Set to Keep Track of Futures: We maintain a Set of ScheduledFuture<?> to hold references to all scheduled tasks.

Override Scheduling Methods: In the overridden schedule and scheduleWithFixedDelay methods, we store each newly created ScheduledFuture in our Set.

Shutdown Method: During the shutdown process, we iterate over the Set and cancel all scheduled tasks. This ensures that they are halted before the application context begins its shutdown operations.

Instantiate the Scheduler in Your Configuration Class
Utilize this custom scheduler within your application configuration class where you define your scheduled tasks:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

The implementation of a custom ThreadPoolTaskScheduler allows developers to effectively manage the lifecycle of scheduled tasks during application shutdown in Spring Boot. By ensuring all tasks are cancelled prior to the context shutting down, we not only clean up the execution of background processes but also mitigate the risk of running into access issues concerning closed resources like the EntityManager.

This solution not only makes your Spring Boot applications more robust but also leads to improved stability and resource management during shutdown operations.

If you're facing similar issues with scheduled tasks in your application, consider implementing a cust