exercise start/stop race conditions

this doesn’t cover all the edge cases of each possible stage for the races, but it gets the basics covered.

jupyterhub/apihandlers/users.py

@@ -231,7 +231,10 @@ class UserServerAPIHandler(APIHandler):
             return
 
         if not spawner.ready:
-            raise web.HTTPError(400, "%s is not running" % spawner._log_name)
+            raise web.HTTPError(
+                400, "%s is not running %s" %
+                (spawner._log_name, '(pending: %s)' % spawner.pending if spawner.pending else '')
+            )
         # include notify, so that a server that died is noticed immediately
         status = yield spawner.poll_and_notify()
         if status is not None:

jupyterhub/handlers/base.py

@@ -514,7 +514,7 @@ class BaseHandler(RequestHandler):
             raise KeyError("User %s has no such spawner %r", user.name, name)
         spawner = user.spawners[name]
         if spawner.pending:
-            raise RuntimeError("%s pending %s" % (user_server_name, spawner.pending))
+            raise RuntimeError("%s pending %s" % (spawner._log_name, spawner.pending))
         # set user._stop_pending before doing anything async
         # to avoid races
         spawner._stop_pending = True

jupyterhub/tests/test_api.py

@@ -654,6 +654,50 @@ def test_active_server_limit(app, request):
     assert counts['pending'] == 0
 
 
+@mark.gen_test
+def test_start_stop_race(app, no_patience, slow_spawn):
+    user = add_user(app.db, app, name='panda')
+    spawner = user.spawner
+    # start the server
+    r = yield api_request(app, 'users', user.name, 'server', method='post')
+    assert r.status_code == 202
+    assert spawner.pending == 'spawn'
+    # additional spawns while spawning shouldn't trigger a new spawn
+    with mock.patch.object(spawner, 'start') as m:
+        r = yield api_request(app, 'users', user.name, 'server', method='post')
+    assert r.status_code == 202
+    assert m.call_count == 0
+
+    # stop while spawning is not okay
+    r = yield api_request(app, 'users', user.name, 'server', method='delete')
+    assert r.status_code == 400
+    while not spawner.ready:
+        yield gen.sleep(0.1)
+
+    spawner.delay = 3
+    # stop the spawner
+    r = yield api_request(app, 'users', user.name, 'server', method='delete')
+    assert r.status_code == 202
+    assert spawner.pending == 'stop'
+    # make sure we get past deleting from the proxy
+    yield gen.sleep(1)
+    # additional stops while stopping shouldn't trigger a new stop
+    with mock.patch.object(spawner, 'stop') as m:
+        r = yield api_request(app, 'users', user.name, 'server', method='delete')
+    assert r.status_code == 202
+    assert m.call_count == 0
+    # start while stopping is not allowed
+    with mock.patch.object(spawner, 'start') as m:
+        r = yield api_request(app, 'users', user.name, 'server', method='post')
+    assert r.status_code == 400
+
+    while spawner.active:
+        yield gen.sleep(0.1)
+    # start after stop is okay
+    r = yield api_request(app, 'users', user.name, 'server', method='post')
+    assert r.status_code == 202
+
+
 @mark.gen_test
 def test_get_proxy(app):
     r = yield api_request(app, 'proxy')