Fix LogViewer PreRenderQueue error

[tlmii]

Resolves #124

Switch to using a ConcurrentQueue to handle the PreRenderQueue duties.

Also removes an unused method from LogViewer and simplifies the common callstack from WatchLogsAsync -> AddLogEntriesAsync -> WriteLogsAsync to just WatchLogsAsync -> WriteLogsAsync.

[davidfowl]

Where does the concurrency happen?

[tlmii]

Where does the concurrency happen?

The async enumerator iteration in WatchLogsAsync can start up before OnAfterRenderAsync is called and finished (there's a small time between when the LogViewer is available to it's parent but before the LogViewer itself is rendered).

If WatchLogsAsync happens to call WriteLogsAsync while OnAfterRenderAsync is iterating the PreRenderQueue, it will try to add another entry to the queue while in the process of iterating the queue.

Since the old code was just a List, and iteration was a foreach, that threw the exception you saw.

Switching to a Queue (or even just switching to use a for loop) would avoid the exception, but since the problem was of the write-while-reading type, it seemed safer to just go ahead and use a ConcurrentQueue. Its use is limited to the very small window of time before the first rendering of the component (and the OnAfterRenderAsync handler) is complete.

[IEvangelist]

Why not replace the Count > 0 check with the TryDequeue(out logs) instead?

[tlmii]

My understanding (which could be wrong!) was that "it's really empty" is only one of the reasons that TryDequeue can return false. So that's why I kept the normal check to try again if it wasn't actually empty when the TryDequeue failed.

[tlmii]

Read through the code for TryDequeue and it looks like you're right. I think some of the descriptions I read about the use of it just weren't precise enough.