The experimental EmitSync flag can in theory be used to select which implementation of the synchronization primitives to use. The flag was convenient when the various implementations were compared a long time ago.

In practice the only implementation that is used and tested today is the default one. The EmitSync flag no longer serves the purpose it used to, and is "Unsafe, Unstable" (the documentation of the flag says so explicitly). It should be obsoleted and later removed.