Backport thread-local variables from Ruby 2.0

1 files changed, 70 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/core_ext/thread.rb b/activesupport/lib/active_support/core_ext/thread.rb
new file mode 100644
index 0000000000..6ad0b2d69c
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/thread.rb
@@ -0,0 +1,70 @@
+class Thread
+  LOCK = Mutex.new # :nodoc:
+
+  # 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 <tt>"bar"</tt> 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.
+  def thread_variable_get(key)
+    locals[key.to_sym]
+  end
+
+  # Sets a thread local with +key+ to +value+. Note that these are local to
+  # threads, and not to fibers. Please see Thread#thread_variable_get for
+  # more information.
+  def thread_variable_set(key, value)
+    locals[key.to_sym] = value
+  end
+
+  # Returns an 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#thread_variable_get
+  # for more details.
+  def thread_variables
+    locals.keys
+  end
+
+  # Returns <tt>true</tt> 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#thread_variable_get
+  # for more details.
+  def thread_variable?(key)
+    locals.has_key?(key.to_sym)
+  end
+
+  private
+
+  def locals
+    @locals || LOCK.synchronize { @locals ||= {} }
+  end
+end unless Thread.instance_methods.include?(:thread_variable_set)