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@devlead
Created July 9, 2017 18:43
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Sample of using async await in a cake script using a AsyncHelper class to work with all async scenarios, currently needs "--Experimental" flag or to use the Cake.CoreCLR runner as a newer version of Roslyn is required for async to be recognized. Example invocation: cake .\AsyncHelper.cake -Experimental
#load "AsyncHelper.cake"
#r "System.Net.Http"
using System.Net.Http;
using System.Net.Http.Headers;
string url = "https://icanhazdadjoke.com/";
var result = AsyncHelpers.RunSync(
async ()=> {
using(var client = new HttpClient())
{
client.DefaultRequestHeaders
.Accept
.Add(new MediaTypeWithQualityHeaderValue("text/plain"));
using(var r = await client.GetAsync(new Uri(url)))
{
string result = await r.Content.ReadAsStringAsync();
return result;
}
}
}
);
Information(result);
using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
public static class AsyncHelpers
{
/// <summary>
/// Execute's an async Task<T> method which has a void return value synchronously
/// </summary>
/// <param name="task">Task<T> method to execute</param>
public static void RunSync(Func<Task> task)
{
var oldContext = SynchronizationContext.Current;
var synch = new ExclusiveSynchronizationContext();
SynchronizationContext.SetSynchronizationContext(synch);
synch.Post(async _ =>
{
try
{
await task();
}
catch (Exception e)
{
synch.InnerException = e;
throw;
}
finally
{
synch.EndMessageLoop();
}
}, null);
synch.BeginMessageLoop();
SynchronizationContext.SetSynchronizationContext(oldContext);
}
/// <summary>
/// Execute's an async Task<T> method which has a T return type synchronously
/// </summary>
/// <typeparam name="T">Return Type</typeparam>
/// <param name="task">Task<T> method to execute</param>
/// <returns></returns>
public static T RunSync<T>(Func<Task<T>> task)
{
var oldContext = SynchronizationContext.Current;
var synch = new ExclusiveSynchronizationContext();
SynchronizationContext.SetSynchronizationContext(synch);
T ret = default(T);
synch.Post(async _ =>
{
try
{
ret = await task();
}
catch (Exception e)
{
synch.InnerException = e;
throw;
}
finally
{
synch.EndMessageLoop();
}
}, null);
synch.BeginMessageLoop();
SynchronizationContext.SetSynchronizationContext(oldContext);
return ret;
}
private class ExclusiveSynchronizationContext : SynchronizationContext
{
private bool done;
public Exception InnerException { get; set; }
readonly AutoResetEvent workItemsWaiting = new AutoResetEvent(false);
readonly Queue<Tuple<SendOrPostCallback, object>> items =
new Queue<Tuple<SendOrPostCallback, object>>();
public override void Send(SendOrPostCallback d, object state)
{
throw new NotSupportedException("We cannot send to our same thread");
}
public override void Post(SendOrPostCallback d, object state)
{
lock (items)
{
items.Enqueue(Tuple.Create(d, state));
}
workItemsWaiting.Set();
}
public void EndMessageLoop()
{
Post(_ => done = true, null);
}
public void BeginMessageLoop()
{
while (!done)
{
Tuple<SendOrPostCallback, object> task = null;
lock (items)
{
if (items.Count > 0)
{
task = items.Dequeue();
}
}
if (task != null)
{
task.Item1(task.Item2);
if (InnerException != null) // the method threw an exeption
{
throw new AggregateException("AsyncHelpers.Run method threw an exception.", InnerException);
}
}
else
{
workItemsWaiting.WaitOne();
}
}
}
public override SynchronizationContext CreateCopy()
{
return this;
}
}
}
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