// Listing 13.# Parallel Fork/Join using TPL DataFlow
public static async Task <R> ForkJoin <T1, T2, R>(
this IEnumerable <T1> source, Func <T1, Task <IEnumerable <T2> > > map,
Func <R, T2, Task <R> > aggregate, R initialState, // #A
CancellationTokenSource cts = null,
int partitionLevel = 8, int boundCapacity = 20) // #B
{
cts = cts ?? new CancellationTokenSource();
var blockOptions = new ExecutionDataflowBlockOptions
{
MaxDegreeOfParallelism = partitionLevel,
BoundedCapacity = boundCapacity,
CancellationToken = cts.Token
}; // #C
var inputBuffer = new BufferBlock <T1>(
new DataflowBlockOptions
{
CancellationToken = cts.Token,
BoundedCapacity = boundCapacity
}); // #D
var mapperBlock = new TransformManyBlock <T1, T2>(map, blockOptions);
var reducerAgent = Agent.Start(initialState, aggregate, cts);
var linkOptions = new DataflowLinkOptions {
PropagateCompletion = true
};
inputBuffer.LinkTo(mapperBlock, linkOptions);
IDisposable disposable = mapperBlock.AsObservable()
.Subscribe(async item => await reducerAgent.Send(item)); // #E
foreach (var item in source)
{
await inputBuffer.SendAsync(item); // #F
}
inputBuffer.Complete();
var tcs = new TaskCompletionSource <R>();
await inputBuffer.Completion.ContinueWith(task => mapperBlock.Complete());
await mapperBlock.Completion.ContinueWith(task =>
{
var agent = reducerAgent as StatefulDataflowAgent <R, T2>;
disposable.Dispose();
tcs.SetResult(agent.State);
}); // #G
return(await tcs.Task);
}
