Class WorkerGroup

java.lang.Object

org.cojen.tupl.util.WorkerGroup

public abstract class WorkerGroup
extends Object

A group of workers for running tasks. This class isn't thread safe for enqueuing tasks, and so the caller must provide its own mutual exclusion to protect against concurrent enqueues.

Although this class behaves somewhat like a general purpose thread pool, the actual behavior is different. When adding tasks into a thread pool, any thread can be selected for running the task. A WorkerGroup is best used for managing collections of tasks which must run on the same thread, and in a specific order. When using a general purpose thread pool, these tasks would need to synchronize with each other, leading to contention.

When using a WorkerGroup, the first task in the collection should be enqueued as normal, but all of the remaining tasks should be enqueued directly into the selected worker. This ensures that one thread will run the tasks, and in the correct order. Worker threads are shared among many task collections, and execution is interleaved. Care must be taken to avoid creating stalled tasks, since this can stall the execution of unrelated tasks.

Method Summary

Modifier and Type	Method	Description
abstract Worker	enqueue(Worker.Task task)	Enqueue a task, blocking if necessary until space is available.
abstract void	interrupt()	Interrupts all the workers.
abstract void	join(boolean interrupt)	Waits until all the worker queues are drained.
static WorkerGroup	make(int workerCount, int maxSize, long keepAliveTime, TimeUnit unit, ThreadFactory threadFactory)
abstract Worker	tryEnqueue(Worker.Task task)	Attempts to select an available worker and enqueues a task without blocking.

Methods inherited from class java.lang.Object

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

Method Details

make

public static WorkerGroup make(int workerCount,
 int maxSize,
 long keepAliveTime,
 TimeUnit unit,
 ThreadFactory threadFactory)

Parameters:

workerCount - number of workers

maxSize - maximum amount of tasks which can be enqueued per worker

keepAliveTime - maximum idle time before worker threads exit

unit - keepAliveTime time unit per worker

threadFactory - null for default

tryEnqueue

public abstract Worker tryEnqueue(Worker.Task task)

Attempts to select an available worker and enqueues a task without blocking. When the task object is enqueued, it must not be used again for any other tasks.

Returns:

selected worker or null if all worker queues are full and task wasn't enqueued

enqueue

public abstract Worker enqueue(Worker.Task task)

Enqueue a task, blocking if necessary until space is available. When the task object is enqueued, it must not be used again for any other tasks.

Returns:

selected worker

join

public abstract void join(boolean interrupt)

Waits until all the worker queues are drained. If the worker threads are interrupted and exit, new threads are started when new tasks are enqueued. The same mutual exclusion rules for enqueueing apply to this method too.

Parameters:

interrupt - pass true to interrupt the worker threads so that they exit

interrupt

public abstract void interrupt()

Interrupts all the workers.