A Java.Util.Concurrent.ThreadPoolExecutor that can additionally schedule commands to run after a given delay, or to execute periodically. This class is preferable to Java.Util.Timer when multiple worker threads are needed, or when the additional flexibility or capabilities of Java.Util.Concurrent.ThreadPoolExecutor (which this class extends) are required.

Delayed tasks execute no sooner than they are enabled, but without any real-time guarantees about when, after they are enabled, they will commence. Tasks scheduled for exactly the same execution time are enabled in first-in-first-out (FIFO) order of submission.

When a submitted task is cancelled before it is run, execution is suppressed. By default, such a cancelled task is not automatically removed from the work queue until its delay elapses. While this enables further inspection and monitoring, it may also cause unbounded retention of cancelled tasks.

Successive executions of a task scheduled via scheduleAtFixedRate or scheduleWithFixedDelay do not overlap. While different executions may be performed by different threads, the effects of prior executions those of subsequent ones.

While this class inherits from Java.Util.Concurrent.ThreadPoolExecutor, a few of the inherited tuning methods are not useful for it. In particular, because it acts as a fixed-sized pool using corePoolSize threads and an unbounded queue, adjustments to maximumPoolSize have no useful effect. Additionally, it is almost never a good idea to set corePoolSize to zero or use allowCoreThreadTimeOut because this may leave the pool without threads to handle tasks once they become eligible to run.

Extension notes: This class overrides the ThreadPoolExecutor.Execute(Java.Lang.IRunnable) and AbstractExecutorService.Submit(Java.Lang.IRunnable) methods to generate internal Java.Util.Concurrent.IScheduledFuture objects to control per-task delays and scheduling. To preserve functionality, any further overrides of these methods in subclasses must invoke superclass versions, which effectively disables additional task customization. However, this class provides alternative protected extension method decorateTask (one version each for Runnable and Callable) that can be used to customize the concrete task types used to execute commands entered via execute, submit, schedule, scheduleAtFixedRate, and scheduleWithFixedDelay. By default, a ScheduledThreadPoolExecutor uses a task type extending Java.Util.Concurrent.FutureTask. However, this may be modified or replaced using subclasses of the form:

public class CustomScheduledExecutor extends ScheduledThreadPoolExecutor {

   static class CustomTask implements RunnableScheduledFuture { ... 

   protected  RunnableScheduledFuture decorateTask(
                Runnable r, RunnableScheduledFuture task) {
       return new CustomTask(r, task);
   }

   protected  RunnableScheduledFuture decorateTask(
                Callable c, RunnableScheduledFuture task) {
       return new CustomTask(c, task);
   }
   // ... add constructors, etc.
 }}

[Android Documentation]