/
AsyncHelpers.cs
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/
AsyncHelpers.cs
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// Copyright (c) .NET Foundation and Contributors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Adapted from Rebus
using System.Collections.Concurrent;
using System.Runtime.ExceptionServices;
namespace RestSharp;
static class AsyncHelpers {
/// <summary>
/// Executes a task synchronously on the calling thread by installing a temporary synchronization context that queues continuations
/// </summary>
/// <param name="task">Callback for asynchronous task to run</param>
public static void RunSync(Func<Task> task) {
var currentContext = SynchronizationContext.Current;
var customContext = new CustomSynchronizationContext(task);
try {
SynchronizationContext.SetSynchronizationContext(customContext);
customContext.Run();
}
finally {
SynchronizationContext.SetSynchronizationContext(currentContext);
}
}
/// <summary>
/// Executes a task synchronously on the calling thread by installing a temporary synchronization context that queues continuations
/// </summary>
/// <param name="task">Callback for asynchronous task to run</param>
/// <typeparam name="T">Return type for the task</typeparam>
/// <returns>Return value from the task</returns>
public static T RunSync<T>(Func<Task<T>> task) {
T result = default!;
RunSync(async () => { result = await task(); });
return result;
}
/// <summary>
/// Synchronization context that can be "pumped" in order to have it execute continuations posted back to it
/// </summary>
class CustomSynchronizationContext : SynchronizationContext {
readonly ConcurrentQueue<Tuple<SendOrPostCallback, object?>> _items = new();
readonly AutoResetEvent _workItemsWaiting = new(false);
readonly Func<Task> _task;
ExceptionDispatchInfo? _caughtException;
bool _done;
/// <summary>
/// Constructor for the custom context
/// </summary>
/// <param name="task">Task to execute</param>
public CustomSynchronizationContext(Func<Task> task) =>
_task = task ?? throw new ArgumentNullException(nameof(task), "Please remember to pass a Task to be executed");
/// <summary>
/// When overridden in a derived class, dispatches an asynchronous message to a synchronization context.
/// </summary>
/// <param name="function">Callback function</param>
/// <param name="state">Callback state</param>
public override void Post(SendOrPostCallback function, object? state) {
_items.Enqueue(Tuple.Create(function, state));
_workItemsWaiting.Set();
}
/// <summary>
/// Enqueues the function to be executed and executes all resulting continuations until it is completely done
/// </summary>
public void Run() {
async void PostCallback(object? _) {
try {
await _task().ConfigureAwait(false);
}
catch (Exception exception) {
_caughtException = ExceptionDispatchInfo.Capture(exception);
throw;
}
finally {
Post(_ => _done = true, null);
}
}
Post(PostCallback, null);
while (!_done) {
if (_items.TryDequeue(out var task)) {
task.Item1(task.Item2);
if (_caughtException == null) {
continue;
}
_caughtException.Throw();
}
else {
_workItemsWaiting.WaitOne();
}
}
}
/// <summary>
/// When overridden in a derived class, dispatches a synchronous message to a synchronization context.
/// </summary>
/// <param name="function">Callback function</param>
/// <param name="state">Callback state</param>
public override void Send(SendOrPostCallback function, object? state) => throw new NotSupportedException("Cannot send to same thread");
/// <summary>
/// When overridden in a derived class, creates a copy of the synchronization context. Not needed, so just return ourselves.
/// </summary>
/// <returns>Copy of the context</returns>
public override SynchronizationContext CreateCopy() => this;
}
}