Race condition in use of _PyOS_SigintEvent on windows

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-04-24.06:55:43.223>
labels = ['interpreter-core', 'type-bug', '3.7', 'OS-windows']
title = 'Race condition in use of _PyOS_SigintEvent on windows'
updated_at = <Date 2017-04-24.07:18:05.541>
user = 'https://github.com/njsmith'

bugs.python.org fields:

activity = <Date 2017-04-24.07:18:05.541>
actor = 'eryksun'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core', 'Windows']
creation = <Date 2017-04-24.06:55:43.223>
creator = 'njs'
dependencies = []
files = []
hgrepos = []
issue_num = 30151
keywords = []
message_count = 2.0
messages = ['292196', '292197']
nosy_count = 5.0
nosy_names = ['paul.moore', 'tim.golden', 'njs', 'zach.ware', 'steve.dower']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue30151'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7']