From: 3han5chou7@...
Date: 2018-02-14T04:12:49+00:00
Subject: [ruby-core:85540] [Ruby trunk Bug#14472] `File::open` closes the file too early when used with callcc

Issue #14472 has been updated by blackenedgold (Sunrin SHIMURA).


I used raw continuations for the simplicity of explanation but I found it was a bit confusing (and I was also confused).

> ... code above must be the same as code below, which works fine:

It was wrong. and

> You can do it by `File.open` without a block.

is absolutely correct.

I wrote wrong code. I intended to write code with [delimited continuations](http://d.hatena.ne.jp/ku-ma-me/20080417/p1) like below.

~~~ ruby
require 'continuation'

def shift
  callcc {|c1| $ctn.(yield(proc {|v| callcc {|c2| $ctn = c2; c1.(v) } })) }
end

def reset
  callcc {|c| $ctn = c; v = yield; $ctn.(v) }
end

reset do
  f1 = shift {|k| File::open("test1", 'w') {|f| k.(f)}}
  f1.write("hello")
end

~~~

*This* is exactly the same as

~~~ ruby
File::open("test1", 'w') {|f1| f1.write("hello")}
~~~

including file is closed after the write is done.


----------------------------------------
Bug #14472: `File::open` closes the file too early when used with callcc
https://bugs.ruby-lang.org/issues/14472#change-70330

* Author: blackenedgold (Sunrin SHIMURA)
* Status: Rejected
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.3.3p222 (2016-11-21) [x86_64-linux-gnu]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
First of all, I know `callcc` is deprecated feature and I'm not in trouble with this bug.
I was just curious and happened to find this bug.

# Bug Description

This code throws an IOError, but expected to exit normally:

~~~ ruby
require 'continuation'
f1 = callcc {|k| File::open("test1", 'w') {|f| k.(f)}}
f1.write("hello")
~~~

~~~
$ ruby openfile_cont.rb                   
/usr/lib/x86_64-linux-gnu/ruby/2.3.0/continuation.so: warning: callcc is obsolete; use Fiber instead
openfile_cont.rb:14:in `write': closed stream (IOError)
        from openfile_cont.rb:14:in `<main>'
~~~

I think this is a bug because the code above must be the same as code below, which works fine:

~~~ ruby
File::open("test1", 'w') {|f1| f1.write("hello")}
~~~

In fact, an equivalent scheme code works fine:

~~~scheme
(let* ((f1 (call/cc (lambda (k) (call-with-output-file "test1" k)))))
  (display "hello" f1))
~~~

~~~
$ gosh openfile_cont.scm 
$ cat test1 
hello
~~~


# Importance
Again, I'm not in trouble with this bug.

The bugging code is useful to rewrite nested `open` blocks to flat style like this:

~~~ ruby
File::open("test1", 'w') do |f1|
  File::open("test2", 'w') do |f2|
    f1.write("hello")
    f2.write("hello")
  end
end

~~~

~~~ ruby
f1 = callcc {|k| File::open("test1", 'w') {|f| k.(f)}}
f2 = callcc {|k| File::open("test2", 'w') {|f| k.(f)}}
f1.write("hello")
f2.write("hello")
~~~

Or, even code that cannot be written with nested `open`s can be written with callcc:

~~~ ruby
["test1", "test2", "test3"].map{|path| callcc {|k| File::open(path, 'w') {|f| k.(f)}}}.each do |f|
  f.write("hello")
end
~~~

Again, equivalent scheme code works fine:

~~~
(let ((paths '("test1" "test2" "test3")))
 (let ((ports (map (lambda (path) (call/cc (lambda (k) (call-with-output-file path k)))) paths)))
   (dolist (port ports)
           (display "hello" port))))
~~~




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