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C# Language : Task Parallel Library


Curious Bot - December 1, 2018 - 0 comments

Parallel.ForEach

An example that uses Parallel.ForEach loop to ping a given array of website urls.

static void Main()
{
string [] urls =
{
"www.stackoverflow.com",
"www.google.net",
"www.facebook.com",
"www.twitter.com"
};

System.Threading.Tasks.Parallel.ForEach(urls, url =>
{
var ping = new System.Net.NetworkInformation.Ping();

var result = ping.Send(url);

if (result.Status == System.Net.NetworkInformation.IPStatus.Success)
{
Console.WriteLine(string.Format("{0} is online", url));
}
});
}

Parallel.For

An example that uses Parallel.For loop to ping a given array of website urls.

static void Main()
{
string [] urls =
{
"www.stackoverflow.com",
"www.google.net",
"www.facebook.com",
"www.twitter.com"
};

System.Threading.Tasks.Parallel.For(0, urls.Length, i =>
{
var ping = new System.Net.NetworkInformation.Ping();

var result = ping.Send(urls[i]);

if (result.Status == System.Net.NetworkInformation.IPStatus.Success)
{
Console.WriteLine(string.Format("{0} is online", urls[i]));
}
});
}

Parallel.Invoke

Invoking methods or actions in parallel (Parallel region)

static void Main()
{
string [] urls =
{
"www.stackoverflow.com",
"www.google.net",
"www.facebook.com",
"www.twitter.com"
};

System.Threading.Tasks.Parallel.Invoke(
() => PingUrl(urls[0]),
() => PingUrl(urls[1]),
() => PingUrl(urls[2]),
() => PingUrl(urls[3])
);
}

void PingUrl(string url)
{
var ping = new System.Net.NetworkInformation.Ping();

var result = ping.Send(url);

if (result.Status == System.Net.NetworkInformation.IPStatus.Success)
{
Console.WriteLine(string.Format("{0} is online", url));
}
}

An async cancellable polling Task that waits between iterations

public class Foo
{
private const int TASK_ITERATION_DELAY_MS = 1000;
private CancellationTokenSource _cts;

public Foo()
{
this._cts = new CancellationTokenSource();
}

public void StartExecution()
{
Task.Factory.StartNew(this.OwnCodeCancelableTask_EveryNSeconds, this._cts.Token);
}

public void CancelExecution()
{
this._cts.Cancel();
}

/// <summary>
/// "Infinite" loop that runs every N seconds. Good for checking for a heartbeat or updates.
/// </summary>
/// <param name="taskState">The cancellation token from our _cts field, passed in the StartNew call</param>
private async void OwnCodeCancelableTask_EveryNSeconds(object taskState)
{
var token = (CancellationToken)taskState;

while (!token.IsCancellationRequested)
{
Console.WriteLine("Do the work that needs to happen every N seconds in this loop");

// Passing token here allows the Delay to be cancelled if your task gets cancelled.
await Task.Delay(TASK_ITERATION_DELAY_MS, token);
}
}
}

A cancellable polling Task using CancellationTokenSource

public class Foo
{
private CancellationTokenSource _cts;

public Foo()
{
this._cts = new CancellationTokenSource();
}

public void StartExecution()
{
Task.Factory.StartNew(this.OwnCodeCancelableTask, this._cts.Token);
}

public void CancelExecution()
{
this._cts.Cancel();
}

/// <summary>
/// "Infinite" loop with no delays. Writing to a database while pulling from a buffer for example.
/// </summary>
/// <param name="taskState">The cancellation token from our _cts field, passed in the StartNew call</param>
private void OwnCodeCancelableTask(object taskState)
{
var token = (CancellationToken) taskState; //Our cancellation token passed from StartNew();

while ( !token.IsCancellationRequested )
{
Console.WriteLine("Do your task work in this loop");
}
}
}

Async version of PingUrl

    static void Main(string[] args)
{
string url = "www.stackoverflow.com";
var pingTask = PingUrlAsync(url);
Console.WriteLine($"Waiting for response from {url}");
Task.WaitAll(pingTask);
Console.WriteLine(pingTask.Result);
}

static async Task<string> PingUrlAsync(string url)
{
string response = string.Empty;
var ping = new System.Net.NetworkInformation.Ping();

var result = await ping.SendPingAsync(url);

await Task.Delay(5000); //simulate slow internet

if (result.Status == System.Net.NetworkInformation.IPStatus.Success)
{
response = $"{url} is online";
}

return response;
}

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