An option for SimpleAsyncTaskExecutor to throw an exception when limit is reached

[dsteb]

Hello,

Use-case:

1. We have an @Async @Retryable task that may fail (e.g. during an incident).
2. If it fails, we retry N times for M seconds.
3. Given N, M and RPS, there can be hundred thousands of pending @Async tasks.
4. We would like to limit concurrency by several thousands, and reject over-limit tasks without affecting a caller of @Async method (without blocking the caller or failing the caller).
5. We would like to use Virtual Threads.

Using default SimpleAsyncTaskExecutor with concurrencyLimit is not an option as it blocks the caller when limit is reached.

Using ThreadPoolExecutor with Virtual Threads is an option, but it is considered an anti-pattern.

Another option is not to use @Async, but just use virtual threads with a semaphore for example.

Is it possible to implement an option for SimpleAsyncTaskExecutor to throw some TaskRejectedException when limit is reached instead of blocking the caller?

[jhoeller]

Good idea! I've introduced a corresponding rejectTasksWhenLimitReached flag on SimpleAsyncTaskExecutor.

This will be available in the upcoming 6.2.6 snapshot in a few minutes. Feel free to give it an early try!