If the number of tasks is floating (from units to hundreds), what type of thread pool should be chosen?

If the number of tasks is variable and can range from a few to hundreds, it is optimal to use a thread pool with a dynamic size, such as ThreadPoolExecutor with scaling capabilities.

In Java, the ThreadPoolExecutor class is suitable for this, where you can set the minimum and maximum number of threads, as well as a task queue. When the load increases, the pool will automatically create new threads up to the maximum, and when it decreases, it will reduce their number.

An example of creating such a pool:

int corePoolSize = 5;
int maximumPoolSize = 100;
long keepAliveTime = 60L;
BlockingQueue<Runnable> workQueue = new LinkedBlockingQueue<>();

ThreadPoolExecutor executor = new ThreadPoolExecutor(
    corePoolSize,
    maximumPoolSize,
    keepAliveTime,
    TimeUnit.SECONDS,
    workQueue
);

This approach allows efficient resource utilization, adapting to the current load, and avoiding unnecessary thread creation when the number of tasks is small.