org.elkoserver.foundation.run
Class SlowServiceRunner

java.lang.Object
  org.elkoserver.foundation.run.SlowServiceRunner

public class SlowServiceRunner
extends Object

This class provides a mechanism for safely making use of external services that are only available via synchronous, blocking (i.e., slow) interfaces. It maintains a thread pool in which calls to such services run, delivering their results back via callback thunks that are dropped onto the normal server run queue.

Constructor Summary

SlowServiceRunner(Runner resultRunner, int maxPoolSize)
Constructor.

Method Summary

void	enqueueTask(Callable<Object> task, ArgRunnable resultHandler) Enqueue a task to be executed via the slow path.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

SlowServiceRunner

public SlowServiceRunner(Runner resultRunner,
                         int maxPoolSize)

Constructor. Note that while this is a constructable class, in practice it should usually be managed as a singleton, i.e., don't mak more than one.

Parameters:

resultRunner - Run queue in which result handlers will be run

maxPoolSize - Maximum number of threads allowed in the thread pool

Method Detail

enqueueTask

public void enqueueTask(Callable<Object> task,
                        ArgRunnable resultHandler)

Enqueue a task to be executed via the slow path. Unlike most code running in our environment, tasks run via this mechanism *are* allowed to invoke operations that can block. However, they are not allowed to lock or reference any normal mutable server state. Since there is not really any graceful way to enforce the latter rule, tasks are on their honor to be well behaved!

Tasks should return a result object that will be passed to the given result handler for execution in the main server run queue. It is permissible for a task result to be null. However, if a task throws an exception, this will be given to the handler as the result, so if the normal task result is an exception type, it is up to the programmer of the task and the result handler to take measures to sort things out appropriately.

Parameters:

task - Callable that executes the task. This will be executed in a separate thread.

resultHandler - Thunk that will be invoked with the result returned by the task. This will be executed on the main run queue.