Package com.spotify.futures

Class ConcurrencyReducer<T>

java.lang.Object

com.spotify.futures.ConcurrencyReducer<T>

public class ConcurrencyReducer<T>
extends Object

ConcurrencyReducer is used to queue tasks which will be executed in a manner reducing the number of concurrent tasks. Note: This is a port of ConcurrencyLimiter from futures-extra for use with CompletionStages

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	ConcurrencyReducer.CapacityReachedException
private static class	ConcurrencyReducer.Job<T>

Field Summary

Fields

Modifier and Type	Field	Description
private final Semaphore	limit
private final int	maxConcurrency
private final int	maxQueueSize
private final BlockingQueue<ConcurrencyReducer.Job<T>>	queue

Constructor Summary

Constructors

Modifier	Constructor	Description
private	ConcurrencyReducer(int maxConcurrency, int maxQueueSize)

Method Summary

Modifier and Type	Method	Description
CompletableFuture<T>	add(Callable<? extends CompletionStage<T>> callable)	the callable function will run as soon as the currently active set of futures is less than the maxConcurrency limit.
static <T> ConcurrencyReducer<T>	create(int maxConcurrency, int maxQueueSize)
private ConcurrencyReducer.Job<T>	grabJob()	Does one of two things: 1) return a job and acquire a permit from the semaphore 2) return null and does not acquire a permit from the semaphore
private void	invoke(CompletableFuture<T> response, Callable<? extends CompletionStage<T>> callable)
int	numActive()
int	numQueued()
private void	pump()
int	remainingActiveCapacity()
int	remainingQueueCapacity()

Methods inherited from class java.lang.Object

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

Field Details

queue

private final BlockingQueue<ConcurrencyReducer.Job<T>> queue

limit

private final Semaphore limit

maxQueueSize

private final int maxQueueSize

maxConcurrency

private final int maxConcurrency

Constructor Details

ConcurrencyReducer

private ConcurrencyReducer(int maxConcurrency,
 int maxQueueSize)

Method Details

create

public static <T> ConcurrencyReducer<T> create(int maxConcurrency,
 int maxQueueSize)

Parameters:

maxConcurrency - maximum number of futures in progress,

maxQueueSize - maximum number of jobs in queue. This is a soft bound and may be temporarily exceeded if add() is called concurrently.

Returns:

a new concurrency limiter

add

public CompletableFuture<T> add(Callable<? extends CompletionStage<T>> callable)

the callable function will run as soon as the currently active set of futures is less than the maxConcurrency limit.

Parameters:

callable - - a function that creates a future.

Returns:

a proxy future that completes with the future created by the input function. This future will be immediately failed with ConcurrencyReducer.CapacityReachedException if the soft queue size limit is exceeded.

numQueued

public int numQueued()

Returns:

the number of callables that are queued up and haven't started yet.

numActive

public int numActive()

Returns:

the number of currently active futures that have not yet completed.

remainingQueueCapacity

public int remainingQueueCapacity()

Returns:

the number of additional callables that can be queued before failing.

remainingActiveCapacity

public int remainingActiveCapacity()

Returns:

the number of additional callables that can be run without queueing.

grabJob

private ConcurrencyReducer.Job<T> grabJob()

Does one of two things: 1) return a job and acquire a permit from the semaphore 2) return null and does not acquire a permit from the semaphore

pump

private void pump()

invoke

private void invoke(CompletableFuture<T> response,
 Callable<? extends CompletionStage<T>> callable)