class Thread

for more details.
Note that these are not fiber local variables. Please see Thread#thread_variable_get

me.thread_variable?(:stanley) # => false
me.thread_variable?(:oliver) # => true
me.thread_variable_set(:oliver, "a")
me = Thread.current

thread-local variable.
Returns true if the given string (or symbol) exists as a

def thread_variable?(key)
  _locals.has_key?(key.to_sym)
end