Fix Heartbeat logging after disposal

[mconnew]

Fix Heartbeat logging after disposal

Prevent Heartbeat from logging exceptions after disposal.
Fix timer loop so disposal check is immediately before heartbeat execution.

Description

During CoreWCF (based on aspnetcore) unit tests we have an ILogger built on ITestOutputHelper which will abort the test run if something is logged after the test has completed execution. The Heartbeat class can log after Dispose() has been called, which means our test run is getting aborted.

This change fixes 2 issues. First, the existing implementation called Thread.Sleep between the disposal check and calling the heart beat handlers which means the handlers can easily get called after the host has been stopped. Then in the handler code, if there's an exception it would always log even if it was disposed.

Fixes #47577

[mconnew]

I added an initial Thread.Sleep before the timer loop to avoid a potential breaking change. The previous code guaranteed a Thread.Sleep call before the first invocation of OnHeatbeat. I wanted to avoid the possibility of any latent issues of a heartbeat handler failing if called too soon. This change maintains this behavior.

[JamesNK]

Seems ok to me.

Off-topic to PR but related to this area: It seems wasteful that the heartbeat thread can sleep for 5 seconds 1 second after the app is stopped. Thread.Sleep can't be canceled. Instead, have we considered using a WaitHandle that can be triggered on stop to exit the TimerLoop immediately?

@halter73 @Tratcher @BrennanConroy

[mconnew]

Isn't it only 1 second?

[danmoseley]

Thread.Sleep can't be canceled.

I put this in the other issue but I believe Thread.Interrupt will cancel it. Of course you have to have the thread object.