Error from Metricreader::Collect at shutdown when using PeriodicExportingMetricReader

[timwoj]

Describe your environment
macOS Ventura, otel-cpp 1.8.3

Steps to reproduce
Run the metrics_simple example

What is the expected behavior?
Example should run without error printouts

What is the actual behavior?
During shutdown, the error MetricReader::Collect invoked while Shutdown in progress! is printed.

Additional context
I found this while implementing metrics in a project I work on, but I then discovered that the metrics_simple example does the same.

I’m using a PeriodicExportingMetricReader. An lldb run confirms that PeriodicExportingMetricReader::OnShutDown is being called, but the log message is emitted during the join() call there on the thread. A backtrace shows that OnShutDown is called from MetricReader::Shutdown(), but that doesn’t happen until after MetricReader::shutdown_ is already set to true. If PeriodicExportingMetricReader::OnShutDown does one more call to Collect during the join (which I wouldn’t be surprised if it does), then it’s going to always output that error.

[lalitb]

The PeriodicExportingMetricReader is supposed to do one last metric collect after shutdown is invoked. But you are right, that last collect would never happen, and will fail with the error. This needs to be fixed.