MySQL Bugs: #110789: OpenAsync throws unhandled exception from thread pool

Bug #110789	OpenAsync throws unhandled exception from thread pool
Submitted:	24 Apr 2023 18:17	Modified:	15 Jul 1:04
Reporter:	Bradley Grainger (OCA)	Email Updates:
Status:	Closed	Impact on me:	None
Category:	Connector / NET	Severity:	S2 (Serious)
Version:	8.0.33, 8.3.0	OS:	Windows (10)
Assigned to:		CPU Architecture:	Any

Description:
If MySqlConnection.OpenAsync throws a timeout exception, it's now thrown from a background threadpool thread and cannot be handled by the application. This can crash the whole process.

With MySql.Data 8.0.32.1, the test program prints the following output (and exits successfully)

Caught MySql.Data.MySqlClient.MySqlException in 00:00:02.1639965
OpenAsync finished in 00:00:02.1655379

With MySql.Data 8.0.33, the test program crashes with an unhandled exception:

Unhandled exception. System.AggregateException: One or more errors occurred. (Timeout expired.  The timeout period elapsed prior to 
completion of the operation or the server is not responding.)
 ---> MySql.Data.MySqlClient.MySqlException (0x80004005): Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.
 ---> System.TimeoutException: The operation has timed out.
   at MySql.Data.Common.StreamCreator.<>c.<GetTcpStreamAsync>b__8_1()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)      
--- End of stack trace from previous location ---
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)      
   at System.Threading.CancellationTokenSource.ExecuteCallbackHandlers(Boolean throwOnFirstException)
   --- End of inner exception stack trace ---
   at System.Threading.CancellationTokenSource.ExecuteCallbackHandlers(Boolean throwOnFirstException)
   at System.Threading.TimerQueueTimer.Fire(Boolean isThreadPool)
   at System.Threading.TimerQueue.FireNextTimers()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart()

It's expected that OpenAsync will return a Task that eventually becomes faulted, so that the application can "await" it and observe the exception.

How to repeat:
Create a "dotnet new console" program and add the following code:

static async Task Main(string[] args)
{
	using var connection = new MySqlConnection("server=www.mysql.com;Connect Timeout=2");
	var stopwatch = Stopwatch.StartNew();
	try
	{
		await connection.OpenAsync();
	}
	catch (Exception ex)
	{
		Console.WriteLine($"Caught {ex.GetType()} in {stopwatch.Elapsed}");
	}
	Console.WriteLine($"OpenAsync finished in {stopwatch.Elapsed}");
}

Hello Bradley Grainger,

Thank you for the bug report.
Verified as described.

Regards,
Ashwini Patil

Bug #114065 marked as duplicate of this one.

Hello.

As reported in Bug #114065, it seems that a similar issue has occurred.
Currently, a timeout occurs when pausing due to debugging, so proper development is not possible with the current version.
When will this bug be fixed?

Also, could you please give me some advice on how to work around this issue?

We welcome your feedback.

Bug #115572 marked as duplicate of this one.

What's the status of this bug ?
It's impacting tremendously on a lot of my customers.

This bug is reproducible with 8.4.0 version as well.
To reproduce it, simply run OpenAsync on a non-reachable MySQL server.
The OpenAsync method would timeout and upon timeout application crashes with System.AggregateException.

InnerException:
MySqlException: Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.

This is affecting application availability. Is there any fix identified for this long pending issue?

Confirming this still exists in 9.2

Posted by developer:
 
Added the following entry to the Connector/NET 9.4.0 changelog: 

"When an application used an asynchronous method and the cancellationToken was triggered, Connector/NET threw an exception from a different thread, which could not be caught and broke the execution. This fix corrected this behavior by throwing the exception in the main thread."

Bug #114257 marked as duplicate of this one.