thread_sync.c (mutex_ptr): handle mutexes held by parent threads in children

Mutexes may be held by threads which only exist in the parent
process, so their waitqueues may be populated with references
to other dead threads.  We must reset them at fork.

I am a moron for introducing this bug :<

[ruby-core:90312] [Bug #15383]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66230 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 21 insertions, 0 deletions

diff --git a/test/ruby/test_thread.rb b/test/ruby/test_thread.rb
index 2b120b4a17..78d6d82e23 100644
--- a/test/ruby/test_thread.rb
+++ b/test/ruby/test_thread.rb
@@ -1239,6 +1239,27 @@ q.pop
     end
   end if Process.respond_to?(:fork)
 
+  def test_fork_while_parent_locked
+    skip 'needs fork' unless Process.respond_to?(:fork)
+    m = Thread::Mutex.new
+    failures = 0
+    run = true
+    thrs = 50.times.map do
+      Thread.new do
+        while run
+          pid = fork { m.synchronize {} }
+          m.synchronize {}
+          _, st = Process.waitpid2(pid)
+          m.synchronize { failures += 1 } unless st.success?
+        end
+      end
+    end
+    sleep 0.5
+    run = false
+    thrs.each(&:join)
+    assert_equal 0, failures, '[ruby-core:90312] [Bug #15383]'
+  end
+
   def test_subclass_no_initialize
     t = Module.new do
       break eval("class C\u{30b9 30ec 30c3 30c9} < Thread; self; end")