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Fix race condition that caused LaunchAsync to never resolve for chrome #2214

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merged 15 commits into from Jun 13, 2023
Merged

Fix race condition that caused LaunchAsync to never resolve for chrome #2214

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ca95043
Fix https://github.com/hardkoded/puppeteer-sharp/issues/2202
leonardo-fernandes May 26, 2023
5a5391b
Change the await to only apply to attachedToTarget, leaving other mes…
leonardo-fernandes May 27, 2023
f58262f
Remove the await for OnAttachedToTarget call, and also included a mis…
leonardo-fernandes May 30, 2023
aabb86e
* Fixed a race condition if a message is received before the Browser.…
leonardo-fernandes Jun 1, 2023
deb351d
Previous commit introduced a new race condition. It was possible that…
leonardo-fernandes Jun 1, 2023
84c3dd5
It was possible for the TargetManager initialization to finish withou…
leonardo-fernandes Jun 2, 2023
dda9812
PR review
leonardo-fernandes Jun 2, 2023
91c5e2b
Rolling back Target.setDiscoverTargets to be sent from the constructor
leonardo-fernandes Jun 10, 2023
7e65695
Handle exceptions in OnAttachedToTarget
leonardo-fernandes Jun 10, 2023
0d3a600
OnAttachedToTarget should be executed synchronously if possible, so t…
leonardo-fernandes Jun 10, 2023
16b9283
Fix PuppeteerConnectTests.ShouldSupportTargetFilter.
leonardo-fernandes Jun 12, 2023
d7d6617
Fix OOPIFTests.ShouldDetectExistingOopifsWhenPuppeteerConnectsToAnExi…
leonardo-fernandes Jun 12, 2023
e8199a6
Revert unintentional line ending changes.
leonardo-fernandes Jun 12, 2023
f22b62a
Merge branch 'hardkoded:master' into master
leonardo-fernandes Jun 12, 2023
1bbb87f
Use the launcher timeout when awaiting for `_targetDiscoveryCompletio…
leonardo-fernandes Jun 12, 2023
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33 changes: 33 additions & 0 deletions lib/PuppeteerSharp.Tests/UtilitiesTests/TaskQueueTests.cs
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Expand Up @@ -49,6 +49,39 @@ public async Task ShouldNotThrowWhenDisposingMultipleTimesAsync()
await taskQueue.DisposeAsync().ConfigureAwait(false);
}

[Fact]
public async Task CanDisposeWhileSemaphoreIsHeld()
{
var taskQueue = new TaskQueue();

await taskQueue.Enqueue(() =>
{
taskQueue.Dispose();
return Task.CompletedTask;
});

var semaphore = GetSemaphore(taskQueue);
Assert.Throws<ObjectDisposedException>(() => semaphore.AvailableWaitHandle);

taskQueue.Dispose();
}

[Fact]
public async Task CanDisposeWhileSemaphoreIsHeldAsync()
{
var taskQueue = new TaskQueue();

await taskQueue.Enqueue(async () =>
{
await taskQueue.DisposeAsync();
});

var semaphore = GetSemaphore(taskQueue);
Assert.Throws<ObjectDisposedException>(() => semaphore.AvailableWaitHandle);

await taskQueue.DisposeAsync();
}

private static SemaphoreSlim GetSemaphore(TaskQueue queue) =>
(SemaphoreSlim)typeof(TaskQueue).GetField("_semaphore", BindingFlags.Instance | BindingFlags.NonPublic).GetValue(queue);
}
Expand Down
20 changes: 6 additions & 14 deletions lib/PuppeteerSharp/Browser.cs
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Expand Up @@ -202,12 +202,6 @@ public async Task<ITarget> WaitForTargetAsync(Func<ITarget, bool> predicate, Wai
}

var timeout = options?.Timeout ?? DefaultWaitForTimeout;
var existingTarget = Targets().FirstOrDefault(predicate);
if (existingTarget != null)
{
return existingTarget;
}

var targetCompletionSource = new TaskCompletionSource<ITarget>(TaskCreationOptions.RunContinuationsAsynchronously);

void TargetHandler(object sender, TargetChangedArgs e)
Expand All @@ -220,17 +214,15 @@ void TargetHandler(object sender, TargetChangedArgs e)

try
{
foreach (var target in Targets())
{
if (predicate(target))
{
return target;
}
}

TargetCreated += TargetHandler;
TargetChanged += TargetHandler;

var existingTarget = Targets().FirstOrDefault(predicate);
if (existingTarget != null)
{
return existingTarget;
}
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return await targetCompletionSource.Task.WithTimeout(timeout).ConfigureAwait(false);
}
finally
Expand Down
57 changes: 37 additions & 20 deletions lib/PuppeteerSharp/ChromeTargetManager.cs
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Expand Up @@ -25,6 +25,9 @@ internal class ChromeTargetManager : ITargetManager
private readonly List<string> _targetsIdsForInit = new();
private readonly TaskCompletionSource<bool> _initializeCompletionSource = new();

// Needed for .NET only to prevent race conditions between StoreExistingTargetsForInit and OnAttachedToTarget
private readonly TaskCompletionSource<bool> _targetDiscoveryCompletionSource = new();

public ChromeTargetManager(
Connection connection,
Func<TargetInfo, CDPSession, Target> targetFactoryFunc,
Expand All @@ -35,8 +38,21 @@ internal class ChromeTargetManager : ITargetManager
_targetFactoryFunc = targetFactoryFunc;
_logger = _connection.LoggerFactory.CreateLogger<ChromeTargetManager>();
_connection.MessageReceived += OnMessageReceived;
_connection.SessionDetached += Connection_SessionDetached;
_connection.SessionDetached += Connection_SessionDetached;
}

public event EventHandler<TargetChangedArgs> TargetAvailable;

public event EventHandler<TargetChangedArgs> TargetGone;

public event EventHandler<TargetChangedArgs> TargetChanged;

public event EventHandler<TargetChangedArgs> TargetDiscovered;

public ConcurrentDictionary<string, Target> GetAvailableTargets() => _attachedTargetsByTargetId;

public async Task InitializeAsync()
{
_ = _connection.SendAsync("Target.setDiscoverTargets", new TargetSetDiscoverTargetsRequest
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Is there a benefit of moving the call to Target.setDiscoverTargets in InitializeAsync instead of having it in the constructor as it is in puppeteer?

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I didn't fully understand this, so I'll have to run more tests to get a better grip at it. But the test PuppeteerConnectTests.ShouldSupportTargetFilter was failing randomly. This test connects to a browser that already has 3 tabs open.

What I found was that the messages of the targets were being processed concurrently, even before the event handlers in AttachAsync were added. Again, ultimately this is due to the multi-threaded .NET vs single-threaded JS difference, as in JS the constructor and the event handlers would be added without any concurrent code.

I will get back to you with a more thorough explanation.

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I agree with the addition of _targetDiscoveryCompletionSource to ensure it has completed before anything else tries to consume _targetsIdsForInit which StoreExistingTargetsForInit populates.

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@jnyrup jnyrup Jun 7, 2023 •
edited

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Another idea, if we move Target.setDiscoverTargets to InitializeAsync anyways, can we use modern async/await syntax and avoid _targetDiscoveryCompletionSource or am I missing some concurrency again?

public async Task InitializeAsync()
{
    var setDiscoverTargetsTask = _connection.SendAsync("Target.setDiscoverTargets", new TargetSetDiscoverTargetsRequest
    {
        Discover = true,
        Filter = new[]
        {
            new TargetSetDiscoverTargetsRequest.DiscoverFilter()
            {
                Type = "tab",
                Exclude = true,
            },
            new TargetSetDiscoverTargetsRequest.DiscoverFilter(),
        },
    });

    await _connection.SendAsync("Target.setAutoAttach", new TargetSetAutoAttachRequest()
    {
        WaitForDebuggerOnStart = true,
        Flatten = true,
        AutoAttach = true,
    }).ConfigureAwait(false);

    try
    {
        await setDiscoverTargetsTask.ConfigureAwait(false);
        StoreExistingTargetsForInit();
    }
    catch (Exception ex)
    {
        _logger.LogError(ex, "Target.setDiscoverTargets failed");
    }

    FinishInitializationIfReady();

    await _initializeCompletionSource.Task.ConfigureAwait(false);
}

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@jnyrup I have reverted these changes and couldn't reproduce any failure in 100 executions of PuppeteerConnectTests.ShouldSupportTargetFilter. Let's see how it behaves in AppVeyor.

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Turns out awaiting for _targetDiscoveryCompletionSource is needed before calling FinishInitializationIfReady(), otherwise FinishInitializationIfReady could execute before any targets have been added to the _targetsIdsForInit collection and the initialization would be considered completed.

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I'm fine with how it's done now 👍

... but if we moved _connection.SendAsync("Target.setDiscoverTargets" to InitializeAsync again and awaited it, like in my example above, I'm failing to see how we can reach FinishInitializationIfReady before setDiscoverTargetsTask has completed, which should remove the need for _targetDiscoveryCompletionSource.

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@jnyrup had a closer look at your code above.

The change seems fine, and it simplifies a few things - for example it uses a try/catch which is more natural than checking t.IsFaulted. It's also closer to how FirefoxTargetManager works.

However, the _targetDiscoveryCompletionSource is still needed, to signal other threads that may be processing a message and executing OnAttachedToTarget.

It also has the downside of diverging from upstream.

I can commit these changes if you agree it's a better solution.

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Ahh, it's those events messing with my brain again...
I now (again) see why _targetDiscoveryCompletionSource still is necessary.

I'll let kblok decide whether to call _connection.SendAsync("Target.setDiscoverTargets" in the constructor of InitializeAsync.

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I think that in this PR, _targetDiscoveryCompletionSource is more important than the location of Target.setDiscoverTargets. I would leave Target.setDiscoverTargets in the constructor as we have in upstream.

We are making some important changes (good changes). But it would be nice to see if we do need to move it to InitializeAsync in isolation. If we see that we need it, we can move it in a new PR.

This PR is looking great. I would merge it after the new WithTimeouts. Thank you @leonardo-fernandes, @jnyrup for the hard work here.

{
Discover = true,
Expand All @@ -52,38 +68,34 @@ internal class ChromeTargetManager : ITargetManager
}).ContinueWith(
t =>
{
if (t.IsFaulted)
try
{
_logger.LogError(t.Exception, "Target.setDiscoverTargets failed");
if (t.IsFaulted)
{
_logger.LogError(t.Exception, "Target.setDiscoverTargets failed");
}
else
{
StoreExistingTargetsForInit();
}
}
else
finally
{
StoreExistingTargetsForInit();
_targetDiscoveryCompletionSource.SetResult(true);
}
},
TaskScheduler.Default);
}

public event EventHandler<TargetChangedArgs> TargetAvailable;

public event EventHandler<TargetChangedArgs> TargetGone;

public event EventHandler<TargetChangedArgs> TargetChanged;

public event EventHandler<TargetChangedArgs> TargetDiscovered;

public ConcurrentDictionary<string, Target> GetAvailableTargets() => _attachedTargetsByTargetId;

public async Task InitializeAsync()
{
await _connection.SendAsync("Target.setAutoAttach", new TargetSetAutoAttachRequest()
{
WaitForDebuggerOnStart = true,
Flatten = true,
AutoAttach = true,
}).ConfigureAwait(false);

await _targetDiscoveryCompletionSource.Task.ConfigureAwait(false);
FinishInitializationIfReady();

await _initializeCompletionSource.Task.ConfigureAwait(false);
}

Expand Down Expand Up @@ -125,14 +137,16 @@ private void StoreExistingTargetsForInit()
}
}

private async void OnMessageReceived(object sender, MessageEventArgs e)
private void OnMessageReceived(object sender, MessageEventArgs e)
{
try
{
switch (e.MessageID)
{
case "Target.attachedToTarget":
await OnAttachedToTarget(sender, e.MessageData.ToObject<TargetAttachedToTargetResponse>(true)).ConfigureAwait(false);
#pragma warning disable CS4014
OnAttachedToTarget(sender, e.MessageData.ToObject<TargetAttachedToTargetResponse>(true)).ConfigureAwait(false);
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#pragma warning restore CS4014
return;
case "Target.detachedFromTarget":
OnDetachedFromTarget(sender, e.MessageData.ToObject<TargetDetachedFromTargetResponse>(true));
Expand Down Expand Up @@ -238,6 +252,8 @@ private async Task OnAttachedToTarget(object sender, TargetAttachedToTargetRespo
}
};

await _targetDiscoveryCompletionSource.Task.ConfigureAwait(false);

if (!_connection.IsAutoAttached(targetInfo.TargetId))
{
return;
Expand All @@ -264,6 +280,7 @@ private async Task OnAttachedToTarget(object sender, TargetAttachedToTargetRespo
_ignoredTargets.Add(targetInfo.TargetId);
FinishInitializationIfReady(targetInfo.TargetId);
await silentDetach().ConfigureAwait(false);
return;
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}

var existingTarget = _attachedTargetsByTargetId.TryGetValue(targetInfo.TargetId, out var target);
Expand Down
33 changes: 29 additions & 4 deletions lib/PuppeteerSharp/Helpers/TaskQueue.cs
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Expand Up @@ -7,6 +7,7 @@ namespace PuppeteerSharp.Helpers
internal sealed class TaskQueue : IDisposable, IAsyncDisposable
{
private readonly SemaphoreSlim _semaphore;
private readonly AsyncLocal<bool> _held = new AsyncLocal<bool>();
private int _disposed;

internal TaskQueue() => _semaphore = new SemaphoreSlim(1);
Expand All @@ -18,7 +19,11 @@ public void Dispose()
return;
}

_semaphore.Wait();
if (!_held.Value)
{
_semaphore.Wait();
}

_semaphore.Dispose();
}

Expand All @@ -29,7 +34,10 @@ public async ValueTask DisposeAsync()
return;
}

await _semaphore.WaitAsync().ConfigureAwait(false);
if (!_held.Value)
{
await _semaphore.WaitAsync().ConfigureAwait(false);
}

_semaphore.Dispose();
}
Expand All @@ -39,11 +47,13 @@ internal async Task<T> Enqueue<T>(Func<Task<T>> taskGenerator)
await _semaphore.WaitAsync().ConfigureAwait(false);
try
{
_held.Value = true;
return await taskGenerator().ConfigureAwait(false);
}
finally
{
_semaphore.Release();
TryRelease(_semaphore);
_held.Value = false;
}
}

Expand All @@ -52,11 +62,26 @@ internal async Task Enqueue(Func<Task> taskGenerator)
await _semaphore.WaitAsync().ConfigureAwait(false);
try
{
_held.Value = true;
await taskGenerator().ConfigureAwait(false);
}
finally
{
_semaphore.Release();
TryRelease(_semaphore);
_held.Value = false;
}
}

private void TryRelease(SemaphoreSlim semaphore)
{
try
{
semaphore.Release();
}
catch (ObjectDisposedException)
{
// If semaphore has already been disposed, then Release() will fail
// but we can safely ignore it
}
}
}
Expand Down