Limit workers to 0 or 1 when using db.simple.api

When using more than one worker, only one of them will return data, thus
leading users to not have access to every single piece of data at once.

Change-Id: I0e7e0f0ff7821465a74eb284e8401ddd7238f6df
Partial-Bug: #1619508
Co-Authored-By: Cyril Roelandt <cyril@redhat.com>
Co-Authored-By: Hemanth Makkapati <hemanth.makkapati@rackspace.com>

doc/source/configuring.rst

@@ -188,7 +188,9 @@ Number of Glance API or Registry worker processes to start. Each worker
 process will listen on the same port. Increasing this value may increase
 performance (especially if using SSL with compression enabled). Typically
 it is recommended to have one worker process per CPU. The value `0`
-will prevent any new processes from being created.
+will prevent any new worker processes from being created. When ``data_api``
+is set to ``glance.db.simple.api``, ``workers`` MUST be set to either ``0`` or
+``1``.
 
 Optional. Default: The number of CPUs available will be used by default.
 

glance/db/simple/api.py

@@ -18,6 +18,7 @@ import copy
 import functools
 import uuid
 
+from oslo_config import cfg
 from oslo_log import log as logging
 import six
 
@@ -27,7 +28,7 @@ from glance.common import utils
 from glance.db import utils as db_utils
 from glance.i18n import _, _LI, _LW
 
-
+CONF = cfg.CONF
 LOG = logging.getLogger(__name__)
 
 DATA = {
@@ -70,6 +71,15 @@ def log_call(func):
     return wrapped
 
 
+def configure():
+    if CONF.workers not in [0, 1]:
+        msg = _('CONF.workers should be set to 0 or 1 when using the '
+                'db.simple.api backend. Fore more info, see '
+                'https://bugs.launchpad.net/glance/+bug/1619508')
+        LOG.critical(msg)
+        raise SystemExit(msg)
+
+
 def reset():
     global DATA
     DATA = {

glance/tests/functional/db/test_simple.py

@@ -20,9 +20,10 @@ import glance.tests.functional.db as db_tests
 from glance.tests.functional.db import base
 
 
-def get_db(config):
+def get_db(config, workers=1):
     CONF.set_override('data_api', 'glance.db.simple.api',
                       enforce_type=True)
+    CONF.set_override('workers', workers, enforce_type=True)
     db_api = glance.db.get_api()
     return db_api
 
@@ -77,3 +78,15 @@ class TestSimpleTask(base.TaskTests,
         db_tests.load(get_db, reset_db)
         super(TestSimpleTask, self).setUp()
         self.addCleanup(db_tests.reset)
+
+
+class TestTooManyWorkers(base.TaskTests):
+
+    def setUp(self):
+        def get_db_too_many_workers(config):
+            self.assertRaises(SystemExit, get_db, config, 2)
+            return get_db(config)
+
+        db_tests.load(get_db_too_many_workers, reset_db)
+        super(TestTooManyWorkers, self).setUp()
+        self.addCleanup(db_tests.reset)