From: maths22@... Date: 2020-05-06T21:39:54+00:00 Subject: [ruby-core:98158] [Ruby master Bug#16835] SIGCHLD + system new behavior on 2.6 Issue #16835 has been updated by maths22 (Jacob Burroughs). jeremyevans0 (Jeremy Evans) wrote in #note-2: > I agree that based on a review of the commit message, this change was unintended, and since the issue was not known previously, it was not documented. > > However, I think the new behavior makes more sense. `system` creates a child process, so when the child process exits, it should trigger a `SIGCLD` trap. That is how `sh` itself works (example assumes `echo` is a shell built-in, and uses CHLD instead of CLD as that is the signal name on the operating system I am using): > > ``` > trap "echo child exit" CHLD > $ echo 1 > 1 > $ /bin/echo 1 > 1 > child exit > ``` > > Other than compatibility with Ruby 2.5 and prior, is there a good reason to follow the historical behavior? Going by https://github.com/ruby/ruby/commit/6b87ac68dba3d8967d76233766a174c8a82813e3 , it seems like it was a deliberate decision in the past to *not* have the SIGCLD signal bubble up. I only found this because it caused a rather hard to track down bug in our code, I don't think we actually intended to rely on this behavior. ---------------------------------------- Bug #16835: SIGCHLD + system new behavior on 2.6 https://bugs.ruby-lang.org/issues/16835#change-85397 * Author: maths22 (Jacob Burroughs) * Status: Open * Priority: Normal * ruby -v: ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-darwin19]` * Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN ---------------------------------------- In rubies < 2.5, the `system` command did not trigger sigchld signal traps. On ruby >= 2.6 it does. This appears to have been introduced by https://github.com/ruby/ruby/commit/054a412d540e7ed2de63d68da753f585ea6616c3 . To observe the change in behavior, run the following code on ruby 2.5 and 2.6: ``` ruby Signal.trap("CLD") { puts "Child died" }; system("true") ``` On ruby 2.5 it won't print anything. On ruby 2.6 it will print "Child died". I believe this is an unintended, undocumented change in behavior, but I may be wrong about that. -- https://bugs.ruby-lang.org/ Unsubscribe: