com.google.common.util.concurrent
Class Executors

java.lang.Object
  com.google.common.util.concurrent.Executors

public class Executors
extends Object

Factory and utility methods for Executor, ExecutorService, and ThreadFactory.

Since:

2009.09.15 tentative

Author:

Eric Fellheimer, Kyle Littlefield, Justin Mahoney

Constructor Summary

Executors()

Method Summary

static void	addDelayedShutdownHook(ExecutorService service, long terminationTimeout, TimeUnit timeUnit) Add a shutdown hook to wait for thread completion in the given service.
static ThreadFactory	daemonThreadFactory() Returns a ThreadFactory which creates daemon threads.
static ThreadFactory	daemonThreadFactory(ThreadFactory factory) Wraps another ThreadFactory, making all new threads daemon threads.
static ExecutorService	getExitingExecutorService(ThreadPoolExecutor executor) Converts the given ThreadPoolExecutor into an ExecutorService that exits when the application is complete.
static ExecutorService	getExitingExecutorService(ThreadPoolExecutor executor, long terminationTimeout, TimeUnit timeUnit) Converts the given ThreadPoolExecutor into an ExecutorService that exits when the application is complete.
static ScheduledExecutorService	getExitingScheduledExecutorService(ScheduledThreadPoolExecutor executor) Converts the given ThreadPoolExecutor into a ScheduledExecutorService that exits when the application is complete.
static ScheduledExecutorService	getExitingScheduledExecutorService(ScheduledThreadPoolExecutor executor, long terminationTimeout, TimeUnit timeUnit) Converts the given ScheduledThreadPoolExecutor into a ScheduledExecutorService that exits when the application is complete.
static ExecutorService	sameThreadExecutor() Creates an executor service that runs each task in the thread that invokes execute/submit, as in ThreadPoolExecutor.CallerRunsPolicy This applies both to individually submitted tasks and to collections of tasks submitted via invokeAll or invokeAny.

Methods inherited from class java.lang.Object

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

Constructor Detail

Executors

public Executors()

Method Detail

getExitingExecutorService

public static ExecutorService getExitingExecutorService(ThreadPoolExecutor executor,
                                                        long terminationTimeout,
                                                        TimeUnit timeUnit)

Converts the given ThreadPoolExecutor into an ExecutorService that exits when the application is complete. It does so by using daemon threads and adding a shutdown hook to wait for their completion.

This is mainly for fixed thread pools. See Executors.newFixedThreadPool(int).

Parameters:

executor - the executor to modify to make sure it exits when the application is finished

terminationTimeout - how long to wait for the executor to finish before terminating the JVM

timeUnit - unit of time for the time parameter

Returns:

an unmodifiable version of the input which will not hang the JVM

getExitingScheduledExecutorService

public static ScheduledExecutorService getExitingScheduledExecutorService(ScheduledThreadPoolExecutor executor,
                                                                          long terminationTimeout,
                                                                          TimeUnit timeUnit)

Converts the given ScheduledThreadPoolExecutor into a ScheduledExecutorService that exits when the application is complete. It does so by using daemon threads and adding a shutdown hook to wait for their completion.

This is mainly for fixed thread pools. See Executors.newScheduledThreadPool(int).

Parameters:

executor - the executor to modify to make sure it exits when the application is finished

terminationTimeout - how long to wait for the executor to finish before terminating the JVM

timeUnit - unit of time for the time parameter

Returns:

an unmodifiable version of the input which will not hang the JVM

addDelayedShutdownHook

public static void addDelayedShutdownHook(ExecutorService service,
                                          long terminationTimeout,
                                          TimeUnit timeUnit)

Add a shutdown hook to wait for thread completion in the given service. This is useful if the given service uses daemon threads, and we want to keep the JVM from exiting immediately on shutdown, instead giving these daemon threads a chance to terminate normally.

Parameters:

service - ExecutorService which uses daemon threads

terminationTimeout - how long to wait for the executor to finish before terminating the JVM

timeUnit - unit of time for the time parameter

getExitingExecutorService

public static ExecutorService getExitingExecutorService(ThreadPoolExecutor executor)

Converts the given ThreadPoolExecutor into an ExecutorService that exits when the application is complete. It does so by using daemon threads and adding a shutdown hook to wait for their completion.

This method waits 120 seconds before continuing with JVM termination, even if the executor has not finished its work.

This is mainly for fixed thread pools. See Executors.newFixedThreadPool(int).

Parameters:

executor - the executor to modify to make sure it exits when the application is finished

Returns:

an unmodifiable version of the input which will not hang the JVM

getExitingScheduledExecutorService

public static ScheduledExecutorService getExitingScheduledExecutorService(ScheduledThreadPoolExecutor executor)

Converts the given ThreadPoolExecutor into a ScheduledExecutorService that exits when the application is complete. It does so by using daemon threads and adding a shutdown hook to wait for their completion.

This method waits 120 seconds before continuing with JVM termination, even if the executor has not finished its work.

This is mainly for fixed thread pools. See Executors.newScheduledThreadPool(int).

Parameters:

executor - the executor to modify to make sure it exits when the application is finished

Returns:

an unmodifiable version of the input which will not hang the JVM

daemonThreadFactory

public static ThreadFactory daemonThreadFactory()

Returns a ThreadFactory which creates daemon threads. This is implemented by wrapping Executors.defaultThreadFactory(), marking all new threads as daemon threads

Returns:

a ThreadFactory which creates daemon threads

daemonThreadFactory

public static ThreadFactory daemonThreadFactory(ThreadFactory factory)

Wraps another ThreadFactory, making all new threads daemon threads.

Parameters:

factory - the ThreadFactory used to generate new threads

Returns:

a new ThreadFactory backed by factory whose created threads are all daemon threads

sameThreadExecutor

public static ExecutorService sameThreadExecutor()

Creates an executor service that runs each task in the thread that invokes execute/submit, as in ThreadPoolExecutor.CallerRunsPolicy This applies both to individually submitted tasks and to collections of tasks submitted via invokeAll or invokeAny. In the latter case, tasks will run serially on the calling thread. Tasks are run to completion before a Future is returned to the caller (unless the executor has been shutdown).

Although all tasks are immediately executed in the thread that submitted the task, this ExecutorService imposes a small locking overhead on each task submission in order to implement shutdown and termination behavior.

The implementation deviates from the ExecutorService specification with regards to the shutdownNow method. First, "best-effort" with regards to canceling running tasks is implemented as "no-effort". No interrupts or other attempts are made to stop threads executing tasks. Second, the returned list will always be empty, as any submitted task is considered to have started execution. This applies also to tasks given to invokeAll or invokeAny which are pending serial execution, even the subset of the tasks that have not yet started execution. It is unclear from the ExecutorService specification if these should be included, and it's much easier to implement the interpretation that they not be. Finally, a call to shutdown or shutdownNow may result in concurrent calls to invokeAll/invokeAny throwing RejectedExecutionException, although a subset of the tasks may already have been executed.