Header only singletons are not working properly for Windows

[marcalff]

The opentelemetry-cpp API uses header only singletons, for example for the tracer provider.

When:

• an application calls TracerProvider::SetTracerProvider() in the main application code
• a shared library is loaded by the main application
• the shared library uses TracerProvider::GetTracerProvider()

the shared library does not see the tracer provider installed in the main application.

As a result, opentelemetry is disabled in the shared library (the noop tracer provider is seen instead).

Related issues:

• Support building DLL for windows  #1105
• Build OpenTelemetry C++ SDK and exporter into DLL #1932
• Fix header only api singletons (#1520) #1604
  • This fixed all platforms except Windows.
• [TEST] Expand api singleton test to cover explicit dlopen(). #2164
  • The test is executed on all platforms except Windows.
• [POC RFC] header only API for singletons (Windows) #1595
• [POC RFC] header only API for singletons #1525

The issue about singletons for the Windows platform is known, but still not resolved.

[malkia]

I've been running the singleton_test in my soft-fork that targets single .dll for Windows (combining sdk+api) - and it's passing in that version. - https://github.com/malkia/opentelemetry-cpp/actions/runs/7878684091/job/21497437677#step:5:8420 - this has been my "test" to ensure that I'm not breaking things across dlls - but I've been relyin on bazel to make the .dll, not CMake (it's what I'm more familiar with).

[github-actions]

This issue was marked as stale due to lack of activity.