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//
// AsyncCriticalSection.cs
//
// Author:
// Lluis Sanchez Gual <lluis@xamarin.com>
//
// Copyright (c) 2015 Xamarin, Inc (http://www.xamarin.com)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
namespace MonoDevelop.Projects
{
/// <summary>
/// A critical section object which can be awaited
/// </summary>
/// <remarks>This critical section is not reentrant.</remarks>
public class AsyncCriticalSection
{
class CriticalSectionDisposer: IDisposable
{
public AsyncCriticalSection AsyncCriticalSection;
public void Dispose ()
{
AsyncCriticalSection.Exit ();
}
}
IDisposable criticalSectionDisposer;
Queue<TaskCompletionSource<IDisposable>> queue = new Queue<TaskCompletionSource<IDisposable>> ();
bool locked;
public AsyncCriticalSection ()
{
criticalSectionDisposer = new CriticalSectionDisposer { AsyncCriticalSection = this };
}
public IDisposable Enter ()
{
return EnterAsync ().Result;
}
public Task<IDisposable> EnterAsync ()
{
lock (queue) {
if (!locked) {
locked = true;
return Task.FromResult (criticalSectionDisposer);
}
// When the TaskCompletionSource's SetResult method is called then all the async continuations waiting
// on this lock may be invoked synchronously. This can cause a stack overflow if many tasks are queued.
// To avoid this the continuations are run asynchronously by creating the TaskCompletionSource with
// TaskCreationOptions.RunContinuationsAsynchronously.
// https://stackoverflow.com/questions/28321457/taskcontinuationoptions-runcontinuationsasynchronously-and-stack-dives
var s = new TaskCompletionSource<IDisposable> (TaskCreationOptions.RunContinuationsAsynchronously);
queue.Enqueue (s);
return s.Task;
}
}
void Exit ()
{
TaskCompletionSource<IDisposable> cs = null;
lock (queue) {
if (queue.Count > 0) {
cs = queue.Dequeue ();
} else
locked = false;
}
// Set the result outside the lock, otherwise this can lead to stack overflow on task continuations.
cs?.SetResult (criticalSectionDisposer);
}
}
}
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