Likely race condition in FileTraceWriter

[paulbatum]

A user on Azure Functions doing a high throughput event hubs scenario reported they often see an exception with the following trace:

System.ArgumentOutOfRangeException: Index and count must refer to a location within the buffer. Parameter name: chars at 
System.Text.EncoderNLS.GetBytes(Char[] chars, Int32 charIndex, Int32
 charCount, Byte[] bytes, Int32 byteIndex, Boolean flush) at 
System.IO.StreamWriter.Flush(Boolean flushStream, Boolean flushEncoder) at
System.IO.StreamWriter.Flush() at 
Microsoft.Azure.WebJobs.Host.CompositeTraceWriter.Flush() at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.<ExecuteWithLoggingAsync>d__14.MoveNext()

 --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task
 task) at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.<TryExecuteAsync>d__12.MoveNext()

(original report here)

From the trace it looks likely that the problem is unsynchronized access to a StreamWriter. Considering that FileTraceWriter has the only non-trivial implementation of TraceWriter.Flush, its the most likely source of the issue.

[fabiocav]

We put a fix in place for this but in a couple of places. @brettsam this looks similar to the StringBuilder bug.

[brettsam]

We had some similar races in the Core SDK, here:

• fixing threading bug in logging azure-webjobs-sdk#849.
• making TextWriterTraceAdapter synchronized azure-webjobs-sdk#1043

It may come from FileTraceWriter, but it's not entirely clear:

• I do see that this also has StringBuilder in the Flush path, but it's not in the stack for the error, which I would expect if it was the same bug. You also get a new StringBuilder with every call to Flush, unlike the above issues.
• FileTraceWriter locks around its writing -- which is a call to File.AppendAllText. I wouldn't expect to see this come from that code.

[AlexLvovsky]

Hi,
Are there any updates about this issue?