On many platforms Unity can use multi-threaded rendering, where actual calls to underlying graphics API are
done on a separate thread. Normally you do not have to worry about this, except if you're making native code
rendering plugins. In that case, you need to make sure your plugin also does rendering calls on the right
thread; use GL.IssuePluginEvent for that.
See Also: GL.IssuePluginEvent, Native Plugin Interface.