Signal the backend that it should emit GC metrics when it has the chance. This should be installed in a GC alarm or another form of regular trigger.

Should be called regularly for background processing, timeout checks, etc.

Give the collector the list of callbacks to be executed when tick() is called. Each such callback should be short and reentrant. Depending on the collector's implementation, it might be called from a thread that is not the one that called on_tick.