thread_variable_get

        # Thread.thread_variable_get

(from ruby core)
---
    thr.thread_variable_get(key)  -> obj or nil

---

Returns the value of a thread local variable that has been set.  Note
that these are different than fiber local values.  For fiber local
values, please see Thread#[] and Thread#[]=.

Thread local values are carried along with threads, and do not respect
fibers.  For example:

    Thread.new {
      Thread.current.thread_variable_set("foo", "bar") # set a thread local
      Thread.current["foo"] = "bar"                    # set a fiber local

      Fiber.new {
        Fiber.yield [
          Thread.current.thread_variable_get("foo"), # get the thread local
          Thread.current["foo"],                     # get the fiber local
        ]
      }.resume
    }.join.value # => ['bar', nil]

The value "bar" is returned for the thread local, where nil is returned
for the fiber local.  The fiber is executed in the same thread, so the
thread local values are available.