Package com.ibm.asyncutil.locks

Class AsyncFunnel<T>

java.lang.Object

com.ibm.asyncutil.locks.AsyncFunnel<T>

public class AsyncFunnel<T>
extends Object

Enforces that a single asynchronous computation occurs at a time, allowing others to observe it.

Used when many clients need the result of an expensive asynchronous operation but only one should be ongoing at any given time. If doOrGet(java.util.function.Supplier<java.util.concurrent.CompletionStage<T>>) is called while an operation is ongoing, the future result of that ongoing task is returned. After the operation completes, a new task can be created.

For example, imagine we have many threads that will perform a computation on a potentially cached value. If the value is not in the cache, they will have to do an expensive operation to populate the cache. Many threads may discover the value needs to be computed at the same time, but only one thread needs to actually compute it.

 
 AsyncFunnel readFunnel = new AsyncFunnel();
 for (int i = 0; i < numThreads; i++) {
    CompletableFuture.supplyAsync(() -> {

        val = readFromCache();
        if (val != null) {
          return StageSupport.completedStage(val);
        }
        // populate the cache if we're first, or just listen for the result on the thread
        // already doing the computation if we're not
        return readFunnel.doOrGet(() -> {
            return expensiveOperation().thenApply(computedVal -> {
                updateCache(readVal);
                return readVal;
            });
        });
    })
 }
 
 

Constructor Summary

Constructors

Constructor	Description
AsyncFunnel()

Method Summary

Modifier and Type	Method	Description
CompletionStage<T>	doOrGet(Supplier<CompletionStage<T>> action)	Runs the provided action, or returns an existing CompletionStage if an action is already running.

Methods inherited from class java.lang.Object

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

Constructor Detail

AsyncFunnel

public AsyncFunnel()

Method Detail

doOrGet

public CompletionStage<T> doOrGet(Supplier<CompletionStage<T>> action)

Runs the provided action, or returns an existing CompletionStage if an action is already running. After the returned stage is completed, the first subsequent doOrGet call will start a new action

Parameters:

action - Supplier of a CompletionStage of T that only runs if no action is currently running

Returns:

A CompletionStage produced by action or one that was previously produced