When to create multiple executor service per application java

Question

When is it a good idea to create more than one executor service per run of a program/application? Why would you do it, instead of just starting up executors.newcachedthreadpool() at the beginning and submitting all callables to it.

Answer 1

• You might need different flavours (say a fixed thread pool or a scheduled executor)
• Encapsulation: if a specific class needs to run things through an executor, it makes sense that this class be responsible to decide its execution policy, which is an implementation detail
• Specialisation - corollary of the previous point:
  • some tasks need many threads (typically network tasks)
  • while others only need a few (CPU-bound task)
  • and some should only use one (if you read/write on your local hard drive for example)
• There certainly are situations where you want to pass an executor to an object because you want the calling code to control how some tasks will be executed

Bottom line, I can't think of a reason why, for a sufficiently large project, you would want to just use one thread pool for your whole program.