Bug #9751: Process.wait does not work correctly in a thread

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: 1.9, 2.0, 2.1, 2.2
• Backport: 2.0.0: DONE, 2.1: DONE

[sam.saffron (Sam Saffron)]

The following code fails under Ruby 1.9+, used to work on 1.8 with green threads

def test
  if pid = fork
    puts "child pid is #{pid} waiting ..."
    begin
      Process.wait(pid)
      puts "child exited"
    rescue => e
      p e
    end
  else
    sleep 3
    puts "exiting child"
    exit 0
  end
end
 
# this works as expected
test
 
puts "testing in thread"
 
# this will hang
Thread.new do
  test
end.join

Additionally on SIGINT I am seeing a zombie + [BUG] pthread_mutex_lock: Invalid argument (EINVAL)

[normalperson (Eric Wong)]

[e-mail] wrote:

def test
  if pid = fork

<snip>

  else
    sleep 3
    puts "exiting child"
    exit 0

A workaround is to use exit!(0) in the child.
Normal "exit" may be buggy, looking into it.

  end
end

[normalperson (Eric Wong)]

The following one-liner fixes the case where "exit" is called.
However, when "exit"/"exit!" is omitted entirely, it still hangs.
I am out of time for today...

--- a/thread.c
+++ b/thread.c
@@ -3799,6 +3799,7 @@ rb_thread_atfork(void)
 {
     rb_thread_atfork_internal(terminate_atfork_i);
     GET_THREAD()->join_list = NULL;
+    GET_THREAD()->tag = NULL;
 
     /* We don't want reproduce CVE-2003-0900. */
     rb_reset_random_seed();

(indented so I hope it looks OK in redmine)

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed
• % Done changed from 0 to 100

Applied in changeset r45899.

---

thread.c: stop if forked in a sub-thread

• thread.c (thread_start_func_2): stop if forked in a sub-thread,
  the thread has become the main thread.
  [ruby-core:62070] [Bug #9751]

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.0.0: UNKNOWN, 2.1: UNKNOWN to 2.0.0: REQUIRED, 2.1: REQUIRED

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.0.0: REQUIRED, 2.1: REQUIRED to 2.0.0: REQUIRED, 2.1: DONE

Backported into ruby_2_1 branch at r46497.

[usa (Usaku NAKAMURA)]

backported into ruby_2_0_0 at r46518.

[usa (Usaku NAKAMURA)]

• Backport changed from 2.0.0: REQUIRED, 2.1: DONE to 2.0.0: DONE, 2.1: DONE