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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
namespace System.Threading.RateLimiting
{
internal sealed class TimerAwaitable : IDisposable, ICriticalNotifyCompletion
{
private Timer? _timer;
private Action? _callback;
private static readonly Action _callbackCompleted = () => { };
private readonly TimeSpan _period;
private readonly TimeSpan _dueTime;
private readonly object _lockObj = new object();
private bool _disposed;
private bool _running = true;
public TimerAwaitable(TimeSpan dueTime, TimeSpan period)
{
_dueTime = dueTime;
_period = period;
}
public void Start()
{
if (_timer == null)
{
lock (_lockObj)
{
if (_disposed)
{
return;
}
if (_timer == null)
{
// Don't capture the current ExecutionContext and its AsyncLocals onto the timer
bool restoreFlow = false;
try
{
if (!ExecutionContext.IsFlowSuppressed())
{
ExecutionContext.SuppressFlow();
restoreFlow = true;
}
_timer = new Timer(static state =>
{
var thisRef = (TimerAwaitable)state!;
thisRef.Tick();
},
state: this,
dueTime: _dueTime,
period: _period);
}
finally
{
// Restore the current ExecutionContext
if (restoreFlow)
{
ExecutionContext.RestoreFlow();
}
}
}
}
}
}
public TimerAwaitable GetAwaiter() => this;
public bool IsCompleted => ReferenceEquals(_callback, _callbackCompleted);
public bool GetResult()
{
_callback = null;
return _running;
}
private void Tick()
{
Action? continuation = Interlocked.Exchange(ref _callback, _callbackCompleted);
continuation?.Invoke();
}
public void OnCompleted(Action continuation)
{
if (ReferenceEquals(_callback, _callbackCompleted) ||
ReferenceEquals(Interlocked.CompareExchange(ref _callback, continuation, null), _callbackCompleted))
{
Task.Run(continuation);
}
}
public void UnsafeOnCompleted(Action continuation)
{
OnCompleted(continuation);
}
public void Stop()
{
lock (_lockObj)
{
// Stop should be used to trigger the call to end the loop which disposes
if (_disposed)
{
throw new ObjectDisposedException(GetType().FullName);
}
_running = false;
}
// Call tick here to make sure that we yield the callback,
// if it's currently waiting, we don't need to wait for the next period
Tick();
}
public void Dispose()
{
lock (_lockObj)
{
_disposed = true;
_timer?.Dispose();
_timer = null;
}
}
}
}
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