Revert back to shared implementation of "locals" storage array.

lib/concurrent-ruby/concurrent/atomic/fiber_local_var.rb

@@ -1,7 +1,40 @@
 require 'concurrent/constants'
+require_relative 'locals'
 
 module Concurrent
  class FiberLocalVar
+ LOCALS = FiberLocals.new(:concurrent_fiber_local_var)
+
+ # @!macro fiber_local_var_method_initialize
+ #
+ # Creates a fiber local variable.
+ #
+ # @param [Object] default the default value when otherwise unset
+ # @param [Proc] default_block Optional block that gets called to obtain the
+ # default value for each fiber
+
+ # @!macro fiber_local_var_method_get
+ #
+ # Returns the value in the current fiber's copy of this fiber-local variable.
+ #
+ # @return [Object] the current value
+
+ # @!macro fiber_local_var_method_set
+ #
+ # Sets the current fiber's copy of this fiber-local variable to the specified value.
+ #
+ # @param [Object] value the value to set
+ # @return [Object] the new value
+
+ # @!macro fiber_local_var_method_bind
+ #
+ # Bind the given value to fiber local storage during
+ # execution of the given block.
+ #
+ # @param [Object] value the value to bind
+ # @yield the operation to be performed with the bound variable
+ # @return [Object] the value
+
  def initialize(default = nil, &default_block)
  if default && block_given?
  raise ArgumentError, "Cannot use both value and block as default value"
@@ -15,20 +48,20 @@ def initialize(default = nil, &default_block)
  @default = default
  end
 
- @name = :"concurrent_variable_#{object_id}"
+ @index = LOCALS.next_index(self)
  end
 
- # @!macro thread_local_var_method_get
+ # @!macro fiber_local_var_method_get
  def value
- Thread.current.fetch(@name) {default}
+ LOCALS.fetch(@index) {default}
  end
 
- # @!macro thread_local_var_method_set
+ # @!macro fiber_local_var_method_set
  def value=(value)
- Thread.current[@name] = value
+ LOCALS.set(@index, value)
  end
 
- # @!macro thread_local_var_method_bind
+ # @!macro fiber_local_var_method_bind
  def bind(value, &block)
  if block_given?
  old_value = self.value

lib/concurrent-ruby/concurrent/atomic/locals.rb

@@ -0,0 +1,188 @@
+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(name_prefix = :concurrent_locals)
+ @free = []
+ @lock = Mutex.new
+ @all_locals = {}
+ @next = 0
+
+ @name = :"#{name_prefix}_#{object_id}"
+ 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(target)
+ index = synchronize do
+ if @free.empty?
+ @next += 1
+ else
+ @free.pop
+ end
+ end
+
+ # When the target goes out of scope, we should free the associated index
+ # and all values stored into it.
+ ObjectSpace.define_finalizer(target, target_finalizer(index))
+
+ return 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_locals.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, default = nil)
+ if locals = self.locals
+ value = locals[index]
+ end
+
+ if value.nil?
+ if block_given?
+ yield
+ else
+ default
+ end
+ elsif value.equal?(NULL)
+ nil
+ else
+ value
+ end
+ end
+
+ def set(index, value)
+ locals = self.locals!
+ locals[index] = (value.nil? ? NULL : value)
+
+ value
+ end
+
+ private
+
+ # When the target index goes out of scope, clean up that slot across all locals currently assigned.
+ def target_finalizer(index)
+ proc do
+ free_index(index)
+ end
+ end
+
+ # When a target (locals) goes out of scope, delete the locals from all known locals.
+ def locals_finalizer(locals_object_id)
+ proc do |locals_id|
+ weak_synchronize do
+ @all_locals.delete(locals_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
+
+ # An array-backed storage of indexed variables per thread.
+ class ThreadLocals < AbstractLocals
+ def locals
+ Thread.current.thread_variable_get(@name)
+ end
+
+ def locals!
+ thread = Thread.current
+ locals = thread.thread_variable_get(@name)
+
+ unless locals
+ locals = thread.thread_variable_set(@name, [])
+ weak_synchronize do
+ @all_locals[locals.object_id] = locals
+ # When the thread goes out of scope, we should delete the associated locals:
+ ObjectSpace.define_finalizer(thread, locals_finalizer(locals.object_id))
+ end
+ end
+
+ return locals
+ end
+ end
+
+ # An array-backed storage of indexed variables per fiber.
+ class FiberLocals < AbstractLocals
+ def locals
+ Thread.current[@name]
+ end
+
+ def locals!
+ thread = Thread.current
+ locals = thread[@name]
+
+ unless locals
+ locals = thread[@name] = []
+ weak_synchronize do
+ @all_locals[locals.object_id] = locals
+ # When the thread goes out of scope, we should delete the associated locals:
+ ObjectSpace.define_finalizer(Fiber.current, locals_finalizer(locals.object_id))
+ end
+ end
+
+ return locals
+ end
+ end
+end

lib/concurrent-ruby/concurrent/atomic/thread_local_var.rb

@@ -1,10 +1,42 @@
 require 'concurrent/constants'
+require_relative 'locals'
 
 module Concurrent
 
  # @!macro thread_local_var
  class ThreadLocalVar
+ LOCALS = ThreadLocals.new(:concurrent_fiber_local_var)
+
  # @!macro thread_local_var_method_initialize
+ #
+ # Creates a thread local variable.
+ #
+ # @param [Object] default the default value when otherwise unset
+ # @param [Proc] default_block Optional block that gets called to obtain the
+ # default value for each thread
+
+ # @!macro thread_local_var_method_get
+ #
+ # Returns the value in the current thread's copy of this thread-local variable.
+ #
+ # @return [Object] the current value
+
+ # @!macro thread_local_var_method_set
+ #
+ # Sets the current thread's copy of this thread-local variable to the specified value.
+ #
+ # @param [Object] value the value to set
+ # @return [Object] the new value
+
+ # @!macro thread_local_var_method_bind
+ #
+ # Bind the given value to thread local storage during
+ # execution of the given block.
+ #
+ # @param [Object] value the value to bind
+ # @yield the operation to be performed with the bound variable
+ # @return [Object] the value
+
  def initialize(default = nil, &default_block)
  if default && block_given?
  raise ArgumentError, "Cannot use both value and block as default value"
@@ -18,29 +50,17 @@ def initialize(default = nil, &default_block)
  @default = default
  end
 
- @name = :"concurrent_variable_#{object_id}"
+ @index = LOCALS.next_index(self)
  end
 
  # @!macro thread_local_var_method_get
  def value
- value = Thread.current.thread_variable_get(@name)
-
- if value.nil?
- default
- elsif value.equal?(NULL)
- nil
- else
- value
- end
+ LOCALS.fetch(@index) {default}
  end
 
  # @!macro thread_local_var_method_set
  def value=(value)
- if value.nil?
- value = NULL
- end
-
- Thread.current.thread_variable_set(@name, value)
+ LOCALS.set(@index, value)
  end
 
  # @!macro thread_local_var_method_bind