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Class: Concurrent::FiberLocalVar

Relationships & Source Files
Inherits: Object
Defined in: lib/concurrent-ruby/concurrent/atomic/fiber_local_var.rb

Overview

A FiberLocalVar is a variable where the value is different for each fiber. Each variable may have a default value, but when you modify the variable only the current fiber will ever see that change.

This is similar to Ruby’s built-in fiber-local variables (‘Thread.current`), but with these major advantages:

  • FiberLocalVar has its own identity, it doesn’t need a Symbol.

  • Each Ruby’s built-in fiber-local variable leaks some memory forever (it’s a Symbol held forever on the fiber), so it’s only OK to create a small amount of them. FiberLocalVar has no such issue and it is fine to create many of them.

  • Ruby’s built-in fiber-local variables leak forever the value set on each fiber (unless set to nil explicitly). FiberLocalVar automatically removes the mapping for each fiber once the FiberLocalVar instance is GC’d.

Examples:

v = FiberLocalVar.new(14)
v.value #=> 14
v.value = 2
v.value #=> 2
v = FiberLocalVar.new(14)

Fiber.new do
  v.value #=> 14
  v.value = 1
  v.value #=> 1
end.resume

Fiber.new do
  v.value #=> 14
  v.value = 2
  v.value #=> 2
end.resume

v.value #=> 14

Constant Summary

Class Method Summary

Instance Attribute Summary

Instance Method Summary

Constructor Details

.new(default = nil, &default_block) ⇒ FiberLocalVar

Creates a fiber local variable.

Parameters:

  • default (Object) (defaults to: nil) —

    the default value when otherwise unset

  • default_block (Proc) —

    Optional block that gets called to obtain the default value for each fiber

[ GitHub ] 

  


# File 'lib/concurrent-ruby/concurrent/atomic/fiber_local_var.rb', line 49



def initialize(default = nil, &default_block)
  if default && block_given?
    raise ArgumentError, "Cannot use both value and block as default value"
  end

  if block_given?
    @default_block = default_block
    @default = nil
  else
    @default_block = nil
    @default = default
  end

  @index = LOCALS.next_index(self)
end


  







Instance Attribute Details



  

    #value  ⇒ Object  (rw)
  



  

    

Returns the value in the current fiber’s copy of this fiber-local variable.


  





  
Returns:


    
  
  • 
    (Object)
—    
    

    the current value
    

    
  
    • 





  [ GitHub ]


  

  


# File 'lib/concurrent-ruby/concurrent/atomic/fiber_local_var.rb', line 68



def value
  LOCALS.fetch(@index) { default }
end


  








  

    #value=(value)  ⇒ Object  (rw)
  



  

    

Sets the current fiber’s copy of this fiber-local variable to the specified value.


  





  
Parameters:


    
  
  • 
    value
    (Object)
—    
    

    the value to set
    

    
  
    • 



Returns:





  [ GitHub ]


  

  


# File 'lib/concurrent-ruby/concurrent/atomic/fiber_local_var.rb', line 76



def value=(value)
  LOCALS.set(@index, value)
end


  







Instance Method Details



  

    #bind(value) { ... } ⇒ Object 
  



  

    

Bind the given value to fiber local storage during execution of the given block.


  





  
Parameters:


    
  
  • 
    value
    (Object)
—    
    

    the value to bind
    

    
  
    • 



Yields:


    
  
  • 
    
    
    

    the operation to be performed with the bound variable
    

    
  
    • 



Returns:





  [ GitHub ]


  

  


# File 'lib/concurrent-ruby/concurrent/atomic/fiber_local_var.rb', line 86



def bind(value)
  if block_given?
    old_value = self.value
    self.value = value
    begin
      yield
    ensure
      self.value = old_value
    end
  end
end


  








  

    #default   (private)
  

  [ GitHub ]


  

  


# File 'lib/concurrent-ruby/concurrent/atomic/fiber_local_var.rb', line 101



def default
  if @default_block
    self.value = @default_block.call
  else
    @default
  end
end