Moved thread local var classes into own files.

Author: jdantonio

lib/concurrent/atomic/abstract_thread_local_var.rb

@@ -0,0 +1,40 @@
+module Concurrent
+
+  # @!macro thread_local_var
+  # @!macro internal_implementation_note
+  # @!visibility private
+  class AbstractThreadLocalVar
+
+    # @!visibility private
+    NIL_SENTINEL = Object.new
+    private_constant :NIL_SENTINEL
+
+    # @!macro thread_local_var_method_initialize
+    def initialize(default = nil)
+      @default = default
+      allocate_storage
+    end
+
+    # @!macro thread_local_var_method_get
+    def value
+      raise NotImplementedError
+    end
+
+    # @!macro thread_local_var_method_set
+    def value=(value)
+      raise NotImplementedError
+    end
+
+    # @!macro thread_local_var_method_bind
+    def bind(value, &block)
+      raise NotImplementedError
+    end
+
+    protected
+
+    # @!visibility private
+    def allocate_storage
+      raise NotImplementedError
+    end
+  end
+end

lib/concurrent/atomic/java_thread_local_var.rb

@@ -0,0 +1,50 @@
+require 'concurrent/atomic/abstract_thread_local_var'
+
+if Concurrent.on_jruby?
+
+  module Concurrent
+
+    # @!visibility private
+    # @!macro internal_implementation_note
+    class JavaThreadLocalVar < AbstractThreadLocalVar
+
+      # @!macro thread_local_var_method_get
+      def value
+        value = @var.get
+
+        if value.nil?
+          @default
+        elsif value == NIL_SENTINEL
+          nil
+        else
+          value
+        end
+      end
+
+      # @!macro thread_local_var_method_set
+      def value=(value)
+        @var.set(value)
+      end
+
+      # @!macro thread_local_var_method_bind
+      def bind(value, &block)
+        if block_given?
+          old_value = @var.get
+          begin
+            @var.set(value)
+            yield
+          ensure
+            @var.set(old_value)
+          end
+        end
+      end
+
+      protected
+
+      # @!visibility private
+      def allocate_storage
+        @var = java.lang.ThreadLocal.new
+      end
+    end
+  end
+end

lib/concurrent/atomic/ruby_thread_local_var.rb

@@ -0,0 +1,172 @@
+require 'thread'
+require 'concurrent/atomic/abstract_thread_local_var'
+
+module Concurrent
+
+  # @!visibility private
+  # @!macro internal_implementation_note
+  class RubyThreadLocalVar < AbstractThreadLocalVar
+
+    # Each thread has a (lazily initialized) array of thread-local variable values
+    # Each time a new thread-local var is created, we allocate an "index" for it
+    # For example, if the allocated index is 1, that means slot #1 in EVERY
+    #   thread's thread-local array will be used for the value of that TLV
+    #
+    # The good thing about using a per-THREAD structure to hold values, rather
+    #   than a per-TLV structure, is that no synchronization is needed when
+    #    reading and writing those values (since the structure is only ever
+    #    accessed by a single thread)
+    #
+    # Of course, when a TLV is GC'd, 1) we need to recover its index for use
+    #   by other new TLVs (otherwise the thread-local arrays could get bigger
+    #   and bigger with time), and 2) we need to null out all the references
+    #   held in the now-unused slots (both to avoid blocking GC of those objects,
+    #   and also to prevent "stale" values from being passed on to a new TLV
+    #   when the index is reused)
+    # Because we need to null out freed slots, we need to keep references to
+    #   ALL the thread-local arrays -- ARRAYS is for that
+    # But when a Thread is GC'd, we need to drop the reference to its thread-local
+    #   array, so we don't leak memory
+
+    # @!visibility private
+    FREE = []
+    LOCK = Mutex.new
+    ARRAYS = {} # used as a hash set
+    @@next = 0
+    private_constant :FREE, :LOCK, :ARRAYS
+
+    # @!macro [attach] thread_local_var_method_initialize
+    #
+    #   Creates a thread local variable.
+    #
+    #   @param [Object] default the default value when otherwise unset
+    def initialize(default = nil)
+      @default = default
+      allocate_storage
+    end
+
+    # @!macro thread_local_var_method_get
+    def value
+      if array = get_threadlocal_array
+        value = array[@index]
+        if value.nil?
+          @default
+        elsif value.equal?(NIL_SENTINEL)
+          nil
+        else
+          value
+        end
+      else
+        @default
+      end
+    end
+
+    # @!macro thread_local_var_method_set
+    def value=(value)
+      me = Thread.current
+      # We could keep the thread-local arrays in a hash, keyed by Thread
+      # But why? That would require locking
+      # Using Ruby's built-in thread-local storage is faster
+      unless array = get_threadlocal_array(me)
+        array = set_threadlocal_array([], me)
+        LOCK.synchronize { ARRAYS[array.object_id] = array }
+        ObjectSpace.define_finalizer(me, self.class.thread_finalizer(array))
+      end
+      array[@index] = (value.nil? ? NIL_SENTINEL : value)
+      value
+    end
+
+    # @!macro thread_local_var_method_bind
+    def bind(value, &block)
+      if block_given?
+        old_value = self.value
+        begin
+          self.value = value
+          yield
+        ensure
+          self.value = old_value
+        end
+      end
+    end
+
+    protected
+
+    # @!visibility private
+    def allocate_storage
+      @index = LOCK.synchronize do
+        FREE.pop || begin
+        result = @@next
+        @@next += 1
+        result
+        end
+      end
+      ObjectSpace.define_finalizer(self, self.class.threadlocal_finalizer(@index))
+    end
+
+    # @!visibility private
+    def self.threadlocal_finalizer(index)
+      proc do
+        LOCK.synchronize do
+          FREE.push(index)
+          # The cost of GC'ing a TLV is linear in the number of threads using TLVs
+          # But that is natural! More threads means more storage is used per TLV
+          # So naturally more CPU time is required to free more storage
+          ARRAYS.each_value do |array|
+            array[index] = nil
+          end
+        end
+      end
+    end
+
+    # @!visibility private
+    def self.thread_finalizer(array)
+      proc do
+        LOCK.synchronize do
+          # The thread which used this thread-local array is now gone
+          # So don't hold onto a reference to the array (thus blocking GC)
+          ARRAYS.delete(array.object_id)
+        end
+      end
+    end
+
+    private
+
+    if Thread.instance_methods.include?(:thread_variable_get)
+
+      def get_threadlocal_array(thread = Thread.current)
+        thread.thread_variable_get(:__threadlocal_array__)
+      end
+
+      def set_threadlocal_array(array, thread = Thread.current)
+        thread.thread_variable_set(:__threadlocal_array__, array)
+      end
+
+    else
+
+      def get_threadlocal_array(thread = Thread.current)
+        thread[:__threadlocal_array__]
+      end
+
+      def set_threadlocal_array(array, thread = Thread.current)
+        thread[:__threadlocal_array__] = array
+      end
+    end
+
+    # This exists only for use in testing
+    # @!visibility private
+    def value_for(thread)
+      if array = get_threadlocal_array(thread)
+        value = array[@index]
+        if value.nil?
+          @default
+        elsif value.equal?(NIL_SENTINEL)
+          nil
+        else
+          value
+        end
+      else
+        @default
+      end
+    end
+  end
+end