From: ko1@...
Date: 2016-11-05T10:00:43+00:00
Subject: [ruby-core:77966] [Ruby trunk Bug#12607] Ruby needs an atomic	integer

Issue #12607 has been updated by Koichi Sasada.


At first, we need a box of integer, not an atomic integer.

Like that:

```ruby
box = IntegerBox.new(0)
box.increment
box.increment
box.to_i #=> 2
```

This IntegerBox can be implemented by the following code:

```ruby
class IntegerBox
  def initialize n
    @n = n
    @m = Mutex.new
  end
  def increment i = 1
    @m.synchonization{ @n += i }
  end
  def to_i
    @n
  end
end
```

I'm not sure such small part should be include in Ruby's core library.

BTW, concurrent-ruby supports AtomicFixnum <http://ruby-concurrency.github.io/concurrent-ruby/Concurrent/AtomicFixnum.html>.

```
af = Concurrent::AtomicFixnum.new(0)
af.increment
af.increment
af.value #=> 2
```

It has `update` method to set new value. It seems useful.

```
v = af.value
new_v = v + 5
af.update{ new_v }
```

But this small code doesn't work as intended.
This is why I think thread-programming is not easy, even if there is cool threading tools.


----------------------------------------
Bug #12607: Ruby needs an atomic integer
https://bugs.ruby-lang.org/issues/12607#change-61298

* Author: Shyouhei Urabe
* Status: Assigned
* Priority: Normal
* Assignee: Koichi Sasada
* ruby -v: 
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
----------------------------------------
(This one was derived from bug #12463)

Although I don't think += would become atomic, at the same time I understand Rodrigo's needs of _easier_ counter variable that resists inter-thread tampering.  I don't think ruby's Integer class can be used for that purpose for reasons (mainly because it is not designed with threads in mind).  Rather we should introduce a integer class which is carefully designed.

Why not import Concurrent::AtomicFixnum into core?



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