Possible Memory Leak in Async code

[WayneHiller]

I believe I have discovered a memory leak in Http.Async.cs

void SetTimeout(IAsyncResult asyncResult)
        {
            if (Timeout != 0)
                ThreadPool.RegisterWaitForSingleObject(
                    asyncResult.AsyncWaitHandle,
                    TimeoutCallback, _timeoutState, Timeout, true
                );

            static void TimeoutCallback(object state, bool timedOut)
            {
                if (!timedOut)
                    return;

                if (!(state is TimeOutState tos))
                    return;

                lock (tos) tos.TimedOut = true;

                tos.Request?.Abort();
            }
        }

The handle In the call to ThreadPool.RegisterWaitForSingleObject is not saved and handle.Unregister is never called.

https://docs.microsoft.com/en-us/dotnet/api/system.threading.threadpool.registerwaitforsingleobject?view=netcore-3.1

My ANTS Memory Profiler is showing the leak.

Specifications

• Version: 106.10.1
• Platform: Win x64

[WayneHiller]

This could be a fix:

class TimeOutState
{
      public bool TimedOut { get; set; }
      public HttpWebRequest? Request { get; set; }
      public RegisteredWaitHandle Handle = null;
}

...

void SetTimeout(IAsyncResult asyncResult)
        {
            if (Timeout != 0)
                _timeoutState.Handle = ThreadPool.RegisterWaitForSingleObject(
                    asyncResult.AsyncWaitHandle,
                    TimeoutCallback, _timeoutState, Timeout, true
                );

            static void TimeoutCallback(object state, bool timedOut)
            {
                if (!(state is TimeOutState tos))
                    return;

                lock(tos)
                {
                    if(!timedOut)
                    {
                        if(tos.Handle != null)
                        {
                            tos.Handle.Unregister(null);
                        }
                        return;
                    }

                    tos.TimedOut = true;
                }

                tos.Request?.Abort();
            }

[WayneHiller]

I cloned the repo, made the above changes and tested it in my project. The leak was fixed. Any idea why the Repo I cloned is version 106.8.10 but the nuget version I have already in the project is 106.10.1?

[mhornbacher]

Is there a Pull Request for this fix?

[WayneHiller]

I did not create a Pull Request because the version number of the Repo I cloned was older than the release.

[mhornbacher]

@WayneHiller mind if I take a crack at it? Its effecting our production code.

[WayneHiller]

@mhornbacher Go for it.

[alexeyzimarev]

Ok, it's merged, @WayneHiller would you be able to check it against your test with the latest alpha nuget package?

[WayneHiller]

I have since changed the code to use HttpClient, I won't be able to test it. I did test the code above and the leak was fixed.

[mhornbacher]

@alexeyzimarev we deployed this beta package to our QA environment and validated that the memory leak is indeed fixed.

[alexeyzimarev]

@mhornbacher awesome, I will make a fix release soon for the stable package.

[mhornbacher]

Thank you!

Should we close this issue?