Method reader

Lib/test/test_io.py:1095–1099

(file, barrier)

                file.write("x")

        def reader(file, barrier):
            barrier.wait()
            for _ in range(read_count):
                for line in file:
                    self.assertEqual(line, "")

        with self.open(os_helper.TESTFN, "w+") as f:
            barrier = threading.Barrier(thread_count + 1)