Server: Flush console output periodically

[rainersigwald]

This was the intention of the prior call, but _syncWriter.Flush() is
a noop because it's a wrapper around a TextWriter; instead we need to
flush the RedirectConsoleWriter itself, an operation which sends the
accumulated text to the client.

[rainersigwald]

@YuliiaKovalova I was trying to make a nice video of the before/after where this was working/not, but my most recent 8.0.3xx MSBuild didn't reproduce it--I think this regressed from #9983, somehow.

[YuliiaKovalova]

@YuliiaKovalova I was trying to make a nice video of the before/after where this was working/not, but my most recent 8.0.3xx MSBuild didn't reproduce it--I think this regressed from #9983, somehow.

could you please check if reverting this change addresses it?
https://github.com/dotnet/msbuild/pull/9983/files/6ef1733094989a1b8d56bc5d2998061681cf12fb#diff-fc28ca0d80e868e8557a28620998ecee6d7e1def91d231109d4211dd3e4b2ba7

[rainersigwald]

Yup, reverting just that file (and suppressing the warning) fixes the problem. Though I don't see how!

[rainersigwald]

Ah, I see what happened. Before your change, TimerCallback called _syncWriter.Flush() which was a synchronized wrapper over RedirectConsoleWriter.Flush() so it did actually call the "send bits over the pipe" code, and in a thread-safe way since the call would be synchronized.

The current version of this PR fixes it but breaks the thread safety. I think I'll manage the locking manually without Syncronized().

[YuliiaKovalova]

It looks like you address this ticket here:
#10013

[JanKrivanek]

Looks OK.

I'd just probably prefer if the resulting string handling callback is not part of the synchronization here. It doesn't already concern the writer, but rather the external processing of the data (sending them down the pipe)