How to make module specific VERBOSE logging dynamic

[anirbanr-fb]

Today at every VLOG_IS_ON site, we cache a vlocal pointer, which points to FLAGS_v if
vmodule was never used on that binary. If that site's logging has been hit one time, I think
it will point to &FLAGS_v and no more to &google::kLogSiteUninitialized.

This will prevent this site to recache a new value of vlocal which could now have been set
using SetVLOGLevel(). How can we achieve module specific dynamic logging in such a case?

I would like a server to be running with verbose logging FLAGS_v = 0 initially. Then instead of
turning on FLAGS_v globally I would like to be selectively turned on for a few files.

This problem also seems to be captured in the comments on the header file.

// NOTE: To change the log level for VLOG(_IS_ON) sites
// that have already executed after/during InitGoogleLogging,
// one needs to supply the exact --vmodule pattern that applied to them.
// (If no --vmodule pattern applied to them
// the value of FLAGS_v will continue to control them.)

which tells that the dynamic nature of these flags can never be an afterthought.

[sergiud]

This issue should have been fixed by #650.