# \[Bug:trunk\] add explicit constraints for WONTFIX IO bug **URL:** \ **Category:** Development\ **Created:** [February 21, 2010, 4:19pm UTC](https://www.ruby-forum.com/t/bug-trunk-add-explicit-constraints-for-wontfix-io-bug/183839 "2010-02-21T16:19:25Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\ **Post date:** [February 21, 2010, 4:19pm UTC](https://www.ruby-forum.com/t/bug-trunk-add-explicit-constraints-for-wontfix-io-bug/183839/1 "2010-02-21T16:19:25Z")
Hi, all I propose writing two constraints into rdoc of IO: - after running IO#dup, both an original IO and generated IO may cause “bezarre behavior” except IO#close - after running IO#reopen, an original IO that passed to reopen may cause “bezarre behavior” except IO#close In short, it means “IO#dup should not be used” and “IO that was once passed to IO#reopen should be just closed.” “bezarre behavior” does not mean undefined behavior (such as SEGV), but means wrong order of reading and writing, wrong value from IO#pos, etc. (see Appendix) These behaviors are caused by bug of core’s wrong buffering handing. But to fix these, we must change the structure `rb\_io\_t’, public API in include/ruby/io.h, resulting in binary incompatibility. We are currently thinking that these behaviors won’t cause so serious issue to ought to be fixed with even binary incompatibility. So I’m proposing writing the above constraints to assert WONTFIX in the immediate future. Please say your rebuttal if the above constraints make trouble in “real world” example. If valid and convincing rebuttal is come, the issue will be fixed with breaking binary compatibility. If not, the above constraint statement will be added. Answers for anticipated rebuttal: - how to replace stdout and stderr temporarily to invoke subprocess Use Kernel#spawn’s option. - my existing code will not work Please fix your code. Fixing this, _all users_ will be forced to reinstall ext library (even worse, the code of the library may need to be modified). We are expecting rebuttals such as examples that cannot be absorbed by Ruby-level fix or that requires all users to do more cumbersome things. If anyone says no objection in three days, I’ll add the constraints. Thanks, Appendix: current bezarre behaviors of IO#dup and reopen ## foo.txt A B C ## example: first-come-first-served gets after IO#reopen (1) f1 = File.new(“foo.txt”) f2 = File.new(“foo.txt”) f1.reopen(f2) p f1.gets #=\> “A\n” p f2.gets #=\> nil (cannot read) ## example: first-come-first-served gets after IO#reopen (2) f1 = File.new(“foo.txt”) f2 = File.new(“foo.txt”) f1.reopen(f2) p f2.gets #=\> “A\n” p f1.gets #=\> nil (cannot read) ## example: negative value of IO#pos after IO#reopen f1 = File.new(“foo.txt”) f2 = File.new(“foo.txt”) f2.gets f1.reopen(f2) f2.gets f1.rewind p f2.pos #=\> -2 ## example: wrong value of IO#pos after IO#dup f1 = File.new(“foo.txt”) f2 = f1.dup() p f1.pos #=\> 0 p f2.gets #=\> “A\n” p f1.pos #=\> 6 (neither 0 or 2) ## example: IO#pos with side-effect after IO#reopen f1 = File.new(“foo.txt”) f2 = File.new(“foo.txt”) f2.gets f1.reopen(f2) f2.gets p f1.pos #=\> 6 f2.pos p f1.pos #=\> 4 (changed) ## example: wrong order of reading after IO#dup r, w = IO.pipe Thread.new do w.print “Foo\nBar” sleep 1 w.print “Baz\n” sleep 1 w.print “Qux\n” end p r.gets #=\> “Foo\n” r2 = r.dup p r2.gets #=\> “Baz\n” (not “BarBaz\n”) p r.gets #=\> “BarQux\n” (not “Qux\n”) ## example: wrong order of writing after IO#dup f = File.new(“out.txt”, “w”) f1 = File.new(“foo.txt”) f2 = File.new(“foo.txt”) f1.reopen(f) f2.reopen(f) f2.puts(“foo”) f1.puts(“bar”) #=\> resulting “bar\nfoo\n” in out.txt, not “foo\nbar\n” ---
**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\ **Post date:** [February 24, 2010, 3:15pm UTC](https://www.ruby-forum.com/t/bug-trunk-add-explicit-constraints-for-wontfix-io-bug/183839/2 "2010-02-24T15:15:32Z")
2010/2/22 Yusuke ENDOH [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > In short, it means “IO#dup should not be used” and “IO that was once > passed to IO#reopen should be just closed.” > “bezarre behavior” does not mean undefined behavior (such as SEGV), > but means wrong order of reading and writing, wrong value from > IO#pos, etc. (see Appendix) > > These behaviors are caused by bug of core’s wrong buffering handing. I think it is difficult to fix. The “bizarre” behavior can be occur without IO#dup and IO#reopen. By IO.new: % ./ruby -e ’ f1 = File.new(“foo.txt”) f2 = IO.new(f1.fileno) p f1.gets p f2.gets ’ “A\n” nil file descriptors may be shared at outside of ruby: % ./ruby -e ’ f1 = IO.new(3) f2 = IO.new(4) p f1.gets p f2.gets ’ 3\< foo.txt 4\<&3 “A\n” nil file descriptors may be shared between processes: % ( ./ruby -e ‘p STDIN.gets’; ./ruby -e ‘p STDIN.gets’ ) \< foo.txt “A\n” nil This behavior is inherent result of buffering. I think we should live with this behavior because buffering is important for performance. ---
**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\ **Post date:** [February 24, 2010, 4:12pm UTC](https://www.ruby-forum.com/t/bug-trunk-add-explicit-constraints-for-wontfix-io-bug/183839/3 "2010-02-24T16:12:19Z")
Hi, 2010/2/24 Tanaka A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > > These behaviors are caused by bug of core’s wrong buffering handing. > > I think it is difficult to fix. _snip_ > I think we should live with this behavior because > buffering is important for performance. OK, I agree. Then, what should user care to avoid bizarre behavior? IOW, what behavior can be guaranteed? How about: User must not read/write at the time multiple IOs that share the same file descriptor or duplicated file descriptor. Anyway, I think we agreed these bizarre behaviors are WONTFIX. IO#reopen’s spec in rubyspec fails because of this. I’ll soon quarantine! the spec. ---
**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\ **Post date:** [February 25, 2010, 1:07pm UTC](https://www.ruby-forum.com/t/bug-trunk-add-explicit-constraints-for-wontfix-io-bug/183839/4 "2010-02-25T13:07:04Z")
2010/2/25 Yusuke ENDOH [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > Then, what should user care to avoid bizarre behavior? IOW, what behavior > can be guaranteed? How about: > > User must not read/write at the time multiple IOs that share the same > file descriptor or duplicated file descriptor. In most case, STDIN/STDOUT/STDERR are inherited from a parent process. So, they are shared by ruby and the parent. Your idea forbids read/write for STDIN/STDOUT/STDERR. It is too restrictive. I think users should understand following property of I/O operations. - read operations may use buffering. The operations may read more than minimal. - write operations may use buffering. The operations may defer. ---
**Author:** ![Yusuke\_ENDOH](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/c89c15/32.png) [@Yusuke\_ENDOH](https://www.ruby-forum.com/u/Yusuke_ENDOH)\ **Post date:** [March 24, 2010, 6:04pm UTC](https://www.ruby-forum.com/t/bug-trunk-add-explicit-constraints-for-wontfix-io-bug/183839/5 "2010-03-24T18:04:06Z")
Issue #2775 has been updated by Yusuke E… Status changed from Open to Rejected Target version set to 1.9.x ruby -v set to ruby 1.9.2dev (2010-03-24 trunk 27033) [i686-linux] This ticket was rejected. These won’t be fixed. The current spec is explained in [ruby-core:28335] ## – Yusuke E. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) [http://redmine.ruby-lang.org/issues/show/2775](http://redmine.ruby-lang.org/issues/show/2775)