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Effective Java 68 Prefer executors and tasks to threads
Principle
The general mechanism for executing tasks is the executor service. If you think in terms of tasks and let an executor service execute them for you, you gain great flexibility in terms of selecting appropriate execution policies. In essence, the Executor Framework does for execution what the Collections Framework did for aggregation.
Exceutor Framework is a flexible interface-based task execution facility.
Creating work queue with Executor
ExecutorService executor = Executors.newSingleThreadExecutor();
executor.execute(runnable);
Here is how to tell the executor to terminate gracefully (if you fail to do this, it is likely that your VM will not exit):
executor.shutdown();
Usage of executor service
| Usage | Utility |
| Wait for a particular task to complete. | "background thread SetObserver" |
| Wait for any or all of a collection of tasks to complete. | invokeAny or invokeAll methods |
| Wait for the executor service‘s graceful termination to complete. | awaitTermination method |
| Retrive the results of tasks one by one as they complete. | ExecutorCompletionService |
| Control every aspect of a thread pool‘s operation | ThreadPoolExecutor class |
| Small program or lightly loaded server (submitted tasks are not queued but immediately handed off to a thread for execution. If no threads are available, a new one is created. ) | Executors.newCachedThreadPool |
| Heavily loaded production server | Executors.newFixedThreadPool ThreadPoolExecutor |
Thread pool (Fixed or variable service number of threads) .
Task - The key abstraction is the unit of work.
| Task category | return value |
| Runnable | N |
| callable | Y |
|
| Multithread | Time accuracy for long running tasks | Grace recover on uncaught exception |
| java.util.Timer | N | N | N |
| ScheduledThreadPoolExecutor | Y | Y | Y |