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Feature #17323

Updated by ko1 (Koichi Sasada) over 3 years ago

Ruby supports thread and fiber local storage: 

 * `Thread#[sym]` provides *Fiber* local storage 
 * `Thread#thread_variable_get(sym)` `Thread#thread_variable_get(sym) 

 These APIs can access other threads/fibers like that: 

 ```ruby 
 th = Thread.new{ 
   Thread.current.thread_variable_set(:a, 10) 
 } 
 th.join 
 # access from main thread to child thread 
 p th.thread_variable_get(:a) 
 ``` 

 To make Ractor local storage, this kind of feature should not be allowed to protect isolation. 

 This ticket propose alternative API `Ractor::LVar` that allows to provide Ractor local variable. 

 ```ruby 
 LV1 = Ractor::LVar.new 

 p LV1.value #=> nil # default value 
 LV1.value = 'hello' # can set unshareable objects because LVar is ractor local. 

 Ractor.new do 
   LV1.value = 'world' # set Ractor local variable 
 end.take 

 p LV1.value #=> 'hello' 


 # Lvar.new can accept default_proc which should be isolated Proc. 

 LV2 = Ractor::LVar.new{ "x" * 4 } 
 p LV2.value #=> "xxxx" 
 LV2.value = 'yyy' 

 Ractor.new do 
   p LV2.value #=> 'xxx' 
 end 

 p LV2.value #=> 'yyy' 
 ``` 

 This API doesn't support accessing from other ractors. 

 `Ractor::LVar` is from `Ractor::TVar`, but I have no strong opinion about it. 
 For example, `Ractor::LocalVariable` is longer and clearer. 

 Implementation: https://github.com/ruby/ruby/pull/3762 

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