variable.c: cleanup waitq upon thread death

* variable.c (autoload_reset): use idempotent list_del_init
  (autoload_sleep): moved code from rb_autoload_load
  (autoload_sleep_done): cleanup for use with rb_ensure
  (rb_autoload_load): ensure list delete happens in case the
  thread dies during sleep
* test/ruby/bug-13526.rb: new script for separate execution
* test/ruby/test_autoload.rb (test_bug_13526): new test
  [ruby-core:81016] [Bug #13526]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58587 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/bug-13526.rb

@@ -0,0 +1,20 @@
+# From https://bugs.ruby-lang.org/issues/13526#note-1
+
+sleep if $load
+$load = true
+
+n = 10
+threads = Array.new(n) do
+  Thread.new do
+    begin
+      autoload :Foo, "#{File.dirname($0)}/#{$0}"
+      Thread.pass
+      Foo
+    ensure
+      Thread.pass
+    end
+  end
+end
+
+Thread.pass while threads.all?(&:stop?)
+100.times { Thread.pass }

test/ruby/test_autoload.rb

@@ -241,6 +241,11 @@ p Foo::Bar
     end
   end
 
+  def test_bug_13526
+    script = File.join(__dir__, 'bug-13526.rb')
+    assert_ruby_status([script], '', '[ruby-core:81016] [Bug #13526]')
+  end
+
   def add_autoload(path)
     (@autoload_paths ||= []) << path
     ::Object.class_eval {autoload(:AutoloadTest, path)}

variable.c

@@ -2095,7 +2095,7 @@ autoload_reset(VALUE arg)
 	    VALUE th = cur->thread;
 
 	    cur->thread = Qfalse;
-	    list_del(&cur->waitq.node);
+	    list_del_init(&cur->waitq.node); /* idempotent */
 
 	    /*
 	     * cur is stored on the stack of cur->waiting_th,
@@ -2108,6 +2108,34 @@ autoload_reset(VALUE arg)
     return 0;			/* ignored */
 }
 
+static VALUE
+autoload_sleep(VALUE arg)
+{
+    struct autoload_state *state = (struct autoload_state *)arg;
+
+    /*
+     * autoload_reset in other thread will resume us and remove us
+     * from the waitq list
+     */
+    do {
+	rb_thread_sleep_deadly();
+    } while (state->thread != Qfalse);
+
+    return Qfalse;
+}
+
+static VALUE
+autoload_sleep_done(VALUE arg)
+{
+    struct autoload_state *state = (struct autoload_state *)arg;
+
+    if (state->thread != Qfalse && rb_thread_to_be_killed(state->thread)) {
+	list_del_init(&state->waitq.node); /* idempotent */
+    }
+
+    return Qfalse;
+}
+
 VALUE
 rb_autoload_load(VALUE mod, ID id)
 {
@@ -2145,13 +2173,9 @@ rb_autoload_load(VALUE mod, ID id)
     }
     else {
 	list_add_tail(&ele->state->waitq.head, &state.waitq.node);
-	/*
+
-	 * autoload_reset in other thread will resume us and remove us
+	rb_ensure(autoload_sleep, (VALUE)&state,
-	 * from the waitq list
+		autoload_sleep_done, (VALUE)&state);
-	 */
-	do {
-	    rb_thread_sleep_deadly();
-	} while (state.thread != Qfalse);
     }
 
     /* autoload_data_i can be deleted by another thread while require */