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Fixed a null reference exception issue in InternalFireQueuedAsync method and added a fix to support multi-tasks firing triggers #535

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Fixed a null reference exception issue in InternalFireQueuedAsync method and added a fix to support multi-tasks firing triggers #535

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43 changes: 26 additions & 17 deletions src/Stateless/StateMachine.Async.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -135,28 +135,37 @@ async Task InternalFireAsync(TTrigger trigger, params object[] args)
/// <param name="args"> A variable-length parameters list containing arguments. </param>
async Task InternalFireQueuedAsync(TTrigger trigger, params object[] args)
{
if (_firing)
if (!_firing)
{
_eventQueue.Enqueue(new QueuedTrigger { Trigger = trigger, Args = args });
return;
}

try
{
_firing = true;

await InternalFireOneAsync(trigger, args).ConfigureAwait(RetainSynchronizationContext);
await _lock.WaitAsync();

while (_eventQueue.Count != 0)
if(!_firing)
{
var queuedEvent = _eventQueue.Dequeue();
await InternalFireOneAsync(queuedEvent.Trigger, queuedEvent.Args).ConfigureAwait(RetainSynchronizationContext);
try
{
_firing = true;
_lock.Release();
await InternalFireOneAsync(trigger, args).ConfigureAwait(RetainSynchronizationContext);

while (!_eventQueue.IsEmpty)
{
bool suuccess = _eventQueue.TryDequeue(out QueuedTrigger queuedEvent);
if (suuccess)
{
await InternalFireOneAsync(queuedEvent.Trigger, queuedEvent.Args).ConfigureAwait(RetainSynchronizationContext);
}
}
return;
}
finally
{
_firing = false;
}
}
_lock.Release();
}
finally
{
_firing = false;
}

_eventQueue.Enqueue(new QueuedTrigger { Trigger = trigger, Args = args });
}

async Task InternalFireOneAsync(TTrigger trigger, params object[] args)
Expand Down
14 changes: 11 additions & 3 deletions src/Stateless/StateMachine.cs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,9 @@
using Stateless.Reflection;
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Threading;

namespace Stateless
{
Expand Down Expand Up @@ -32,14 +34,15 @@ public partial class StateMachine<TState, TTrigger>
private readonly OnTransitionedEvent _onTransitionCompletedEvent;
private readonly TState _initialState;
private readonly FiringMode _firingMode;
private readonly SemaphoreSlim _lock;

private class QueuedTrigger
{
public TTrigger Trigger { get; set; }
public object[] Args { get; set; }
}

private readonly Queue<QueuedTrigger> _eventQueue = new Queue<QueuedTrigger>();
private readonly ConcurrentQueue<QueuedTrigger> _eventQueue = new ConcurrentQueue<QueuedTrigger>();
private bool _firing;

/// <summary>
Expand Down Expand Up @@ -102,6 +105,7 @@ public StateMachine(TState initialState, FiringMode firingMode) : this()
_unhandledTriggerAction = new UnhandledTriggerAction.Sync(DefaultUnhandledTriggerAction);
_onTransitionedEvent = new OnTransitionedEvent();
_onTransitionCompletedEvent = new OnTransitionedEvent();
_lock = new SemaphoreSlim(1, 1);
}

/// <summary>
Expand Down Expand Up @@ -374,8 +378,12 @@ private void InternalFireQueued(TTrigger trigger, params object[] args)
// Empty queue for triggers
while (_eventQueue.Any())
{
var queuedEvent = _eventQueue.Dequeue();
InternalFireOne(queuedEvent.Trigger, queuedEvent.Args);
bool suuccess = _eventQueue.TryDequeue(out QueuedTrigger queuedEvent);
if(suuccess)
{
InternalFireOne(queuedEvent.Trigger, queuedEvent.Args);
}

}
}
finally
Expand Down
50 changes: 50 additions & 0 deletions test/Stateless.Tests/InitialTransitionFixture.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -335,5 +335,55 @@ public async void AsyncTransitionEvents_OrderingWithInitialTransition()
Assert.Equal(expectedOrdering[i], actualOrdering[i]);
}
}

[Fact]
public async Task CheckMultipleFireAsync()
{
for (int i = 0; i < 200; i++)
{
await CheckAsyncMethod();
}
}

private async Task CheckAsyncMethod()
{
// Create a state machine
var sm = new StateMachine<State, Trigger>(State.A);

sm.Configure(State.A).Permit(Trigger.X, State.B);
sm.Configure(State.A).Permit(Trigger.Y, State.C);
sm.Configure(State.B).Permit(Trigger.Y, State.D);
sm.Configure(State.B).Permit(Trigger.X, State.A);
sm.Configure(State.C).Permit(Trigger.Y, State.D);
sm.Configure(State.C).Permit(Trigger.X, State.A);
sm.Configure(State.D).Permit(Trigger.Y, State.B);
sm.Configure(State.D).Permit(Trigger.X, State.C);


// Create some tasks
List<Task> tasks = new List<Task>();

for (int i = 0; i < 20; i++)
{
Task taskTriggerX = Task.Run(() => FireTrigger(sm, Trigger.X, false));
Task taskTriggerY = Task.Run(() => FireTrigger(sm, Trigger.Y, false));
Task taskTriggerDelay = Task.Run(() => FireTrigger(sm, Trigger.X, true));
tasks.Add(taskTriggerX);
tasks.Add(taskTriggerY);
tasks.Add(taskTriggerDelay);
}

// Wait for tasks to complete
await Task.WhenAll(tasks);
}

private async Task FireTrigger(StateMachine<State, Trigger> sm, Trigger trigger, bool addDelay)
{
if(addDelay)
{
await Task.Delay(20);
}
await sm.FireAsync(trigger);
}
}
}