Commits on Dec 11, 2022

1. Lazily initialize the view package's default worker …

   See discussion in census-instrumentation#1191 for impetus, but in general, it's not
   particularly good practice to start up goroutines in package `init`
   functions, with one reason being that it means that they're started for
   projects that don't even make use of the package, and maybe just have it
   as a transitive dependency.
   
   So here, remove the `view` package's default worker in favor of a new
   function that'll lazily initialize one when any package-level functions
   are called that use the default worker. We use a `sync.Once` that has an
   optimized short-circuit path in case the work's already been done, so
   new overhead should be negligible, and registering/unregistering views
   is probably not a particularly common operation anyway.
   
   This change is backwards compatible, with use of the package's API
   staying exactly the same. Test coverage seems to be pretty good, with a
   function that previously reset the default worker between test cases
   which I've modified to instead reset the default worker back to its
   uninitialized state, and thereby verify that the test cases can
   initialize it if necessary.
   
   I thought about trying to deinitialize the default worker in case its
   last view is unregistered, but decided against it because (1) it's more
   invasive, (2) it's not likely to actually help anyone in practice as
   views probably stay registered for a program's entire duration anwyay,
   and (3) its interaction with the existing package-level `Stop` function
   would take some thinking through.

   

   brandur committed Dec 11, 2022
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