IO#close: do not enqueue redundant interrupts (take #2)

Enqueuing multiple errors for one event causes spurious errors
down the line, as reported by Nikolay Vashchenko in
https://bugs.ruby-lang.org/issues/13632

This should fix bad interactions with test_race_gets_and_close
in test/ruby/test_io.rb since we ensure rb_notify_fd_close
continues returning the busy flag after enqueuing the interrupt.

Backporting changes to 2.4 and earlier releases will be more
challenging...

* thread.c (rb_notify_fd_close): do not enqueue multiple interrupts
  [ruby-core:81581] [Bug #13632]
* test/ruby/test_io.rb (test_single_exception_on_close):
  new test based on script from Nikolay

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59028 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 8 insertions, 2 deletions

diff --git a/thread.c b/thread.c
index da834974bd..cc6e5533c0 100644
--- a/thread.c
+++ b/thread.c
@@ -2212,10 +2212,16 @@ rb_notify_fd_close(int fd)
     list_for_each(&vm->waiting_fds, wfd, wfd_node) {
 	if (wfd->fd == fd) {
 	    rb_thread_t *th = wfd->th;
-	    VALUE err = th->vm->special_exceptions[ruby_error_stream_closed];
+	    VALUE err;
+
+	    busy = 1;
+	    if (!th) {
+		continue;
+	    }
+	    wfd->th = 0;
+	    err = th->vm->special_exceptions[ruby_error_stream_closed];
 	    rb_threadptr_pending_interrupt_enque(th, err);
 	    rb_threadptr_interrupt(th);
-	    busy = 1;
 	}
     }
     return busy;