Chapter 38: TPL Dataflow
Section 38.1: Asynchronous Producer Consumer With A
Bounded Bu erBlock
var bufferBlock = new BufferBlock<int>(new DataflowBlockOptions
{
BoundedCapacity = 1000
});
var cancellationToken = new CancellationTokenSource(TimeSpan.FromSeconds(10)).Token;
var producerTask = Task.Run(async () =>
{
var random = new Random();
while (!cancellationToken.IsCancellationRequested)
{
var value = random.Next();
await bufferBlock.SendAsync(value, cancellationToken);
}
});
var consumerTask = Task.Run(async () =>
{
while (await bufferBlock.OutputAvailableAsync())
{
var value = bufferBlock.Receive(); Console.WriteLine(value);
}
});
await Task.WhenAll(producerTask, consumerTask);
Section 38.2: Posting to an ActionBlock and waiting for completion
// Create a block with an asynchronous action
var block = new ActionBlock<string>(async hostName =>
{
IPAddress[] ipAddresses = await Dns.GetHostAddressesAsync(hostName); Console.WriteLine(ipAddresses[0]);
});
block.Post("google.com"); // Post items to the block's InputQueue for processing block.Post("reddit.com");
block.Post("stackoverflow.com");
block.Complete(); // Tell the block to complete and stop accepting new items
await block.Completion; // Asynchronously wait until all items completed processingu
Section 38.3: Linking blocks to create a pipeline
var httpClient = new HttpClient();
// Create a block the accepts a uri and returns its contents as a string var downloaderBlock = new TransformBlock<string, string>(
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async uri => await httpClient.GetStringAsync(uri));
//Create a block that accepts the content and prints it to the console var printerBlock = new ActionBlock<string>(
contents => Console.WriteLine(contents));
//Make the downloaderBlock complete the printerBlock when its completed.
var dataflowLinkOptions = new DataflowLinkOptions {PropagateCompletion = true};
// Link the block to create a pipeline downloaderBlock.LinkTo(printerBlock, dataflowLinkOptions);
// Post urls to the first block which will pass their contents to the second one. downloaderBlock.Post("http://youtube.com"); downloaderBlock.Post("http://github.com"); downloaderBlock.Post("http://twitter.com");
downloaderBlock.Complete(); // Completion will propagate to printerBlock
await printerBlock.Completion; // Only need to wait for the last block in the pipeline
Section 38.4: Synchronous Producer/Consumer with Bu erBlock<T>
public class Producer
{
private static Random random = new Random((int)DateTime.UtcNow.Ticks);
//produce the value that will be posted to buffer block public double Produce ( )
{
var value = random.NextDouble(); Console.WriteLine($"Producing value: {value}"); return value;
}
}
public class Consumer
{
//consume the value that will be received from buffer block
public void Consume (double value) => Console.WriteLine($"Consuming value: {value}");
}
class Program
{
private static BufferBlock<double> buffer = new BufferBlock<double>(); static void Main (string[] args)
{
//start a task that will every 1 second post a value from the producer to buffer block var producerTask = Task.Run(async () =>
{
var producer = new Producer(); while(true)
{
buffer.Post(producer.Produce()); await Task.Delay(1000);
}
});
//start a task that will recieve values from bufferblock and consume it var consumerTask = Task.Run(() =>
{
var consumer = new Consumer(); while(true)
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{
consumer.Consume(buffer.Receive());
}
});
Task.WaitAll(new[] { producerTask, consumerTask });
}
}
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