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 
    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 
    The operation to invoke for each element.
  • Constructor Summary

    Constructors
    Constructor
    Description
     
  • Method Summary

    Modifier and Type
    Method
    Description
    static <T, R> void
    reverseRun(List<T> list, R zero, AsyncFoldLeft.Operation<T,R> operation, org.cometd.bayeux.Promise<R> promise)
    Processes, in reverse order, the given sequence of elements.
    static <T, R> void
    run(Iterable<T> iterable, R zero, AsyncFoldLeft.Operation<T,R> operation, org.cometd.bayeux.Promise<R> promise)
    Processes the given sequence of elements.
    static <T, R> void
    run(T[] array, R zero, AsyncFoldLeft.Operation<T,R> operation, org.cometd.bayeux.Promise<R> promise)
    Processes the given array of elements.

    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, org.cometd.bayeux.Promise<R> promise)

      Processes the given array of elements.

      Type Parameters:
      T - the type of element
      R - the type of the result
      Parameters:
      array - 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
      See Also:
    • run

      public static <T, R> void run(Iterable<T> iterable, R zero, AsyncFoldLeft.Operation<T,R> operation, org.cometd.bayeux.Promise<R> promise)

      Processes the given sequence of elements.

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

      For each element the operation function is invoked.

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

      Type Parameters:
      T - the type of element
      R - the type of the result
      Parameters:
      iterable - 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
    • reverseRun

      public static <T, R> void reverseRun(List<T> list, R zero, AsyncFoldLeft.Operation<T,R> operation, org.cometd.bayeux.Promise<R> promise)

      Processes, in reverse order, the given sequence of elements.

      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
      See Also: