ArgumentOutOfRangeException when accessing ConnectionMultiplexer log

[paveliak]

Hi

I got an ArgumentOutOfRangeException exception when calling ToString() for the ConnectionMultiplexer log. From the code it looks like all writes to the TextWriter object are synchronized inside the StackExchange.Redis code so the only thing that comes into my mind is that writes might continue after Connect() method returns and then ToString() method collides with those writes. Does it sound plausible?

FWIW we are using v1.2.6.

System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: chunkLength

at System.Text.StringBuilder.ToString()
at System.Text.StringBuilder.AppendFormatHelper(IFormatProvider provider, String format, ParamsArray args)
at System.String.FormatHelper(IFormatProvider provider, String format, ParamsArray args)
...

Here is our code:

var log = new StringWriter();
ConnectionMultiplexer mux = ConnectionMultiplexer.Connect(configurationOptions, log);
Trace($"ConnectionMultiplexerCreated: id={m_id}, log={log}");

Thanks,
Pavel

[mgravell]

My guess here is that there was a delayed operation in a race condition; suggested workaround:

var log = new StringWriter();
ConnectionMultiplexer mux = ConnectionMultiplexer.Connect(configurationOptions, log);
string logText;
lock (log) { logText = log.ToString(); }
Trace($"ConnectionMultiplexerCreated: id={m_id}, log={logText}");

[paveliak]

Thanks @mgravell although I am puzzled how locking on StringWriter object would help here because ConnectionMultiplexer locks on LogSyncLock (different) object when writing into "log".

[mgravell]

Oh, you're right - my bad; I incorrectly remembered what it locked on - I thought it locked on the log. So, er... yeah, that's a fun problem. Let me think on that.

[mgravell]

(for context: from distant memory, I suspect that at one point it did lock on the log instance, and then we hit a problem where someone else was also locking on the log instance, and ... well, bad things)

[mgravell]

I think what I'm going to have to do here is create a proxy to the log object, so that I can wipe it once (inside the lock etc) before leaving Connect/ConnectAsync, and then immediately: any future attempts to write to the log will fail. That's my plan, anyways!

[paveliak]

Sounds good. Meanwhile I will wrap ToString() with try/catch.