The document discusses the Executor Framework in Java for executing tasks asynchronously using threads or executors. It provides examples of submitting runnable tasks to an executor service, waiting for tasks to complete, scheduling tasks, and choosing appropriate executor types for different workloads. It also covers the differences between Runnable and Callable tasks and introduces the ForkJoinPool for splitting tasks recursively into sub-tasks.

1. Effective Java
Item 80: Prefer executors, tasks, and
streams to threads

2. Executor Framework - Basic Example
● Submit a runnable for execution
ExecutorService exec = Executors.newSingleThreadExecutor();
exec.execute(runnable);
exec.shutdown();

3. Executor Framework - invokeAny - Wait until first done

4. Executor Framework - invokeAny - Wait until ALL done

5. Executor Framework - invokeAny - Wait until ALL done
● Hard to get future result by complete sequence

6. Executor Framework - ExecutorCompletionService
● Get future result by sequence

7. Executor Framework - Cancel rest jobs

8. Executor Framework - Schedule task

9. Executor Framework - Choose executor
● Executors.newCachedThreadPool
○ Easy, no configuration
○ Do the right thing
○ When no available thread, new one will be added to pool
○ No task will be queued
○ Choose for small program
■ Why not heavy load program?

10. Executor Framework - Choose executor
● Executors.newCachedThreadPool
○ Easy, no configuration
○ Do the right thing
○ When no available thread, new one will be added to pool
○ No task will be queued
○ Choose for small program
■ Why not heavy load program?
● all of CPUs are fully utilized
● more tasks arrive, more threads will be created
● less CPU available, cause matters worse

11. Executor Framework - Choose executor
● Executors.newFixedThreadPool
○ Gives a pool with fixed number of threads
○ For heavy load program
○ Still need monitor queue size

12. Runnable & Callable
● Runnable: no return value
● Callable: return value

13. ForkJoinPool
● Normal Executor Thread Management
○ Main thread put task to queue
○ Sub tasks put tasks to queue
○ Every task in a queue without boundry
Main
Time

14. ForkJoinPool
● ForkJoinPool Thread Management
○ Main thread create tasks
○ Tasks create sub tasks to fork
○ tasks wait for sub tasks to join
○ Main thread get result or wait for done
Time
task1
Main
task1-1
task1-2
task2
task2-1
task2-2
Time

15. ForkJoinPool Example