[FIXED] Threads are increasing but not decreasing when the task finished in Java

Issue

I have an application that I did thread configuration as follows,

corepoolsize = 10
maxpoolsize = 10
queuecapacity = 10

But when I do use Threads and functions that run on threads (asynchronous process) I see it is increasing like the follows, But I don't see the threads are decreasing. Is that a indication of memory leak? Can anybody guide me?

Log prints like this,

2021-09-15 01:13:48.554  INFO 111 --- [Async-1]
2021-09-15 01:13:48.654  INFO 121 --- [Async-2]
2021-09-15 01:13:48.754  INFO 132 --- [Async-3]
2021-09-15 01:13:48.854  INFO 140 --- [Async-4]
2021-09-15 01:13:48.954  INFO 155 --- [Async-5]
2021-09-15 01:13:49.554  INFO 160 --- [Async-6]

But I don't see it is calling again [Async-1], [Async-2] like that. Is this a memory leak or a thread cache or after filling up corepoolsize then will it run [Async-1]?

Solution

This is expected behaviour. The documentation for ThreadPoolExecutor explicitly states:

When a new task is submitted in method execute(Runnable), if fewer than corePoolSize threads are running, a new thread is created to handle the request, even if other worker threads are idle.

Answered By - Thomas Kläger