Package org.cometd.common

Class AsyncFoldLeft

java.lang.Object

org.cometd.common.AsyncFoldLeft

public class AsyncFoldLeft
extends Object

Processes asynchronously a sequence of elements, producing a result that is the reduction of the results produced by the processing of each element.

This class implements the asynchronous version of the following synchronous for loop, but where the processing of each element may be asynchronous.

 R result;
 for (T element : list) {
     (result, proceed) = operation.apply(result, element);
     if (!proceed) {
         break;
     }
 }
 

Using this class, the loop above becomes:

 R zero;
 AsyncFoldLeft.run(list, zero, (result, element, loop) -> {
     CompletableFuture<R> future = processAsync(element);
     future.whenComplete((r, x) -> {
         if (x == null) {
             R reduced = reduce(result, r);
             if (shouldIterate(r)) {
                 loop.proceed(reduced);
             } else {
                 loop.leave(reduced);
             }
         } else {
             loop.fail(x);
         }
     })
 }, Promise.complete((r, x) -> {
     // Process final result or failure.
 });
 

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	AsyncFoldLeft.Loop<R>	Controls the iteration over a sequence of elements, allowing to continue the iteration (with a result), break out of the iteration (with a result), or fail the iteration (with an exception).
static interface	AsyncFoldLeft.Operation<T,R>	The operation to invoke for each element.

Constructor Summary

Constructors

Constructor	Description
AsyncFoldLeft()

Method Summary

Modifier and Type	Method	Description
static <T, R> void	run(Collection<T> collection, R zero, AsyncFoldLeft.Operation<T,R> operation, Promise<R> promise)	Processes the given collection of elements.
static <T, R> void	run(List<T> list, R zero, AsyncFoldLeft.Operation<T,R> operation, Promise<R> promise)	Deprecated. use run(Collection, Object, Operation, Promise) instead.
static <T, R> void	run(T[] array, R zero, AsyncFoldLeft.Operation<T,R> operation, Promise<R> promise)

Methods inherited from class java.lang.Object

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

Constructor Details

AsyncFoldLeft

public AsyncFoldLeft()

Method Details

run

public static <T, R> void run(T[] array, R zero, AsyncFoldLeft.Operation<T,R> operation, Promise<R> promise)

run

@Deprecated public static <T, R> void run(List<T> list, R zero, AsyncFoldLeft.Operation<T,R> operation, Promise<R> promise)

Deprecated.

use run(Collection, Object, Operation, Promise) instead.

Processes the given list of elements.

The initial result zero is returned if the list is empty.

For each element the operation function is invoked.

Type Parameters:

T - the type of element

R - the type of the result

Parameters:

list - the elements to process

zero - the initial result

operation - the operation to invoke for each element

promise - the promise to notify of the final result

run

public static <T, R> void run(Collection<T> collection, R zero, AsyncFoldLeft.Operation<T,R> operation, Promise<R> promise)

Processes the given collection of elements.

The initial result zero is returned if the collection is empty.

For each element the operation function is invoked.

The collection should have a "stable" iterator, i.e. it should not be affected if the collection is modified concurrently by another thread, or by the same thread in th operation during the iteration.

Type Parameters:

T - the type of element

R - the type of the result

Parameters:

collection - the elements to process

zero - the initial result

operation - the operation to invoke for each element

promise - the promise to notify of the final result