Backport #7720

Process.daemon does not clean up background Ruby threads, leading to hang at exit

Added by Ben Weintraub about 1 year ago. Updated about 1 year ago.

Assignee:Usaku NAKAMURA


Process.fork appears to make special considerations for Ruby background threads so that they are cleaned up in the child process after fork (since fork() only duplicates the calling thread). Process.daemon also relies on fork internally, but does not make the same considerations, leading to a hang at exit in a daemonized process that had multiple Ruby threads prior to calling Process.daemon.

The attached daemon.rb demonstrates the issue. It will call either Process.daemon (default) or Process.fork (if you pass 'fork' as the first arg).

If you pass nothing, causing it to call Process.daemon, the daemonized Ruby process will still think it has two threads, and will hang indefinitely on exit, in a loop in rbthreadterminate_all. If you pass 'fork' as the first argument, the forked child does not hang, and appears to have only one Ruby thread (the one that called Process.fork).

It looks like rbthreadatfork() is the relevant call in the fork case that makes this work, but it doesn't appear to be called in the daemon case.

daemon.rb Magnifier (306 Bytes) Ben Weintraub, 01/22/2013 02:33 AM

Related issues

Duplicated by ruby-trunk - Bug #7798: 子スレッドを実行しているとき Process.daemon すると,その後メインスレッドが終了してもプロセスが終了しない Closed 02/07/2013


#1 Updated by Sam Goldstein about 1 year ago

This seems to be the underlying cause of the bad interaction between resque and new relic described at

#2 Updated by Koichi Sasada about 1 year ago

Does this issue remain on trunk?
(Should we modify trunk before 2.0?)

#3 Updated by Motohiro KOSAKI about 1 year ago

trunk doesn't have an issue. fork and daemon make the same result.

#4 Updated by Usaku NAKAMURA about 1 year ago

  • Status changed from Open to Assigned
  • Assignee set to Usaku NAKAMURA

So, what's the difference?

#5 Updated by Usaku NAKAMURA about 1 year ago

  • Tracker changed from Bug to Backport
  • Project changed from ruby-trunk to Backport93

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