class Thread

# File activesupport/lib/active_support/core_ext/thread.rb, line 72
def freeze
  _locals.freeze
  super
end

Freezes the thread so that thread local variables cannot be set via #thread_variable_set, nor can fiber local variables be set.

me = Thread.current
me.freeze
me.thread_variable_set(:oliver, "a")  #=> RuntimeError: can't modify frozen thread locals
me[:oliver] = "a"                     #=> RuntimeError: can't modify frozen thread locals

# File activesupport/lib/active_support/core_ext/thread.rb, line 61
def thread_variable?(key)
  _locals.has_key?(key.to_sym)
end

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

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

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

# File activesupport/lib/active_support/core_ext/thread.rb, line 25
def thread_variable_get(key)
  _locals[key.to_sym]
end

Returns the value of a thread local variable that has been set. Note that these are different than fiber local values.

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.

# File activesupport/lib/active_support/core_ext/thread.rb, line 32
def thread_variable_set(key, value)
  _locals[key.to_sym] = value
end

Sets a thread local with key to value. Note that these are local to threads, and not to fibers. Please see #thread_variable_get for more information.

# File activesupport/lib/active_support/core_ext/thread.rb, line 47
def thread_variables
  _locals.keys
end

Returns an array of the names of the thread-local variables (as Symbols).

thr = Thread.new do
  Thread.current.thread_variable_set(:cat, 'meow')
  Thread.current.thread_variable_set("dog", 'woof')
end
thr.join               # => #<Thread:0x401b3f10 dead>
thr.thread_variables   # => [:dog, :cat]

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