Add bin and edit workflow

bin/gems/concurrent-ruby-1.3.5/lib/concurrent-ruby/concurrent/atomic/locals.rb

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+require 'fiber'
+require 'concurrent/utility/engine'
+require 'concurrent/constants'
+
+module Concurrent
+  # @!visibility private
+  # @!macro internal_implementation_note
+  #
+  # An abstract implementation of local storage, with sub-classes for
+  # per-thread and per-fiber locals.
+  #
+  # Each execution context (EC, thread or fiber) has a lazily initialized array
+  # of local variable values. Each time a new local variable is created, we
+  # allocate an "index" for it.
+  #
+  # For example, if the allocated index is 1, that means slot #1 in EVERY EC's
+  # locals array will be used for the value of that variable.
+  #
+  # The good thing about using a per-EC structure to hold values, rather than
+  # a global, 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 local variable is GC'd, 1) we need to recover its index
+  # for use by other new local variables (otherwise the locals 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
+  # local when the index is reused).
+  #
+  # Because we need to null out freed slots, we need to keep references to
+  # ALL the locals arrays, so we can null out the appropriate slots in all of
+  # them. This is why we need to use a finalizer to clean up the locals array
+  # when the EC goes out of scope.
+  class AbstractLocals
+    def initialize
+      @free = []
+      @lock = Mutex.new
+      @all_arrays = {}
+      @next = 0
+    end
+
+    def synchronize
+      @lock.synchronize { yield }
+    end
+
+    if Concurrent.on_cruby?
+      def weak_synchronize
+        yield
+      end
+    else
+      alias_method :weak_synchronize, :synchronize
+    end
+
+    def next_index(local)
+      index = synchronize do
+        if @free.empty?
+          @next += 1
+        else
+          @free.pop
+        end
+      end
+
+      # When the local goes out of scope, we should free the associated index
+      # and all values stored into it.
+      ObjectSpace.define_finalizer(local, local_finalizer(index))
+
+      index
+    end
+
+    def free_index(index)
+      weak_synchronize do
+        # The cost of GC'ing a TLV is linear in the number of ECs using local
+        # variables. But that is natural! More ECs means more storage is used
+        # per local variable. So naturally more CPU time is required to free
+        # more storage.
+        #
+        # DO NOT use each_value which might conflict with new pair assignment
+        # into the hash in #set method.
+        @all_arrays.values.each do |locals|
+          locals[index] = nil
+        end
+
+        # free index has to be published after the arrays are cleared:
+        @free << index
+      end
+    end
+
+    def fetch(index)
+      locals = self.locals
+      value = locals ? locals[index] : nil
+
+      if nil == value
+        yield
+      elsif NULL.equal?(value)
+        nil
+      else
+        value
+      end
+    end
+
+    def set(index, value)
+      locals = self.locals!
+      locals[index] = (nil == value ? NULL : value)
+
+      value
+    end
+
+    private
+
+    # When the local goes out of scope, clean up that slot across all locals currently assigned.
+    def local_finalizer(index)
+      proc do
+        free_index(index)
+      end
+    end
+
+    # When a thread/fiber goes out of scope, remove the array from @all_arrays.
+    def thread_fiber_finalizer(array_object_id)
+      proc do
+        weak_synchronize do
+          @all_arrays.delete(array_object_id)
+        end
+      end
+    end
+
+    # Returns the locals for the current scope, or nil if none exist.
+    def locals
+      raise NotImplementedError
+    end
+
+    # Returns the locals for the current scope, creating them if necessary.
+    def locals!
+      raise NotImplementedError
+    end
+  end
+
+  # @!visibility private
+  # @!macro internal_implementation_note
+  # An array-backed storage of indexed variables per thread.
+  class ThreadLocals < AbstractLocals
+    def locals
+      Thread.current.thread_variable_get(:concurrent_thread_locals)
+    end
+
+    def locals!
+      thread = Thread.current
+      locals = thread.thread_variable_get(:concurrent_thread_locals)
+
+      unless locals
+        locals = thread.thread_variable_set(:concurrent_thread_locals, [])
+        weak_synchronize do
+          @all_arrays[locals.object_id] = locals
+        end
+        # When the thread goes out of scope, we should delete the associated locals:
+        ObjectSpace.define_finalizer(thread, thread_fiber_finalizer(locals.object_id))
+      end
+
+      locals
+    end
+  end
+
+  # @!visibility private
+  # @!macro internal_implementation_note
+  # An array-backed storage of indexed variables per fiber.
+  class FiberLocals < AbstractLocals
+    def locals
+      Thread.current[:concurrent_fiber_locals]
+    end
+
+    def locals!
+      thread = Thread.current
+      locals = thread[:concurrent_fiber_locals]
+
+      unless locals
+        locals = thread[:concurrent_fiber_locals] = []
+        weak_synchronize do
+          @all_arrays[locals.object_id] = locals
+        end
+        # When the fiber goes out of scope, we should delete the associated locals:
+        ObjectSpace.define_finalizer(Fiber.current, thread_fiber_finalizer(locals.object_id))
+      end
+
+      locals
+    end
+  end
+
+  private_constant :AbstractLocals, :ThreadLocals, :FiberLocals
+end