refactor(computes): the lock helpers take claims instead of file locks

operations/tests/test_hold.py

@@ -0,0 +1,68 @@
+"""Short operations hold transient claims for their duration; a thread may
+nest them; a job thread holds its job's claims."""
+
+import threading
+
+from django.contrib.auth import get_user_model
+from django.db import connection
+from django.test import TransactionTestCase
+
+from operations import claims
+from operations.models import Claim, Operation
+
+S, X = Claim.SHARED, Claim.EXCLUSIVE
+
+
+class HoldTestCase(TransactionTestCase):
+    def test_claims_live_for_the_block(self):
+        with claims.hold({"instance:u1": X}):
+            self.assertTrue(Claim.objects.filter(resource="instance:u1").exists())
+        self.assertFalse(Claim.objects.exists())
+
+    def test_another_thread_is_refused_at_once(self):
+        inside, release, seen = threading.Event(), threading.Event(), []
+
+        def holder():
+            try:
+                with claims.hold({"instance:u1": X}):
+                    inside.set()
+                    release.wait(10)
+            finally:
+                connection.close()
+
+        t = threading.Thread(target=holder)
+        t.start()
+        self.assertTrue(inside.wait(10))
+        try:
+            with claims.hold({"instance:u1": X}):
+                pass
+        except claims.Busy as busy:
+            seen.append(busy.blocker)
+        finally:
+            release.set()
+            t.join(10)
+        self.assertEqual(seen, [None])
+
+    def test_nesting_in_one_thread_reuses_held_claims(self):
+        with claims.hold({"compute:1": X}):
+            with claims.hold({"compute:1": S, "instance:u1": X}):
+                self.assertEqual(Claim.objects.count(), 2)
+            self.assertEqual(Claim.objects.count(), 1)
+
+    def test_a_shared_claim_cannot_be_upgraded(self):
+        with claims.hold({"compute:1": S}):
+            with self.assertRaisesRegex(RuntimeError, "upgrade"):
+                with claims.hold({"compute:1": X}):
+                    pass
+
+    def test_a_job_thread_holds_its_own_claims(self):
+        user = get_user_model().objects.create_user("hold_user", "h@example.com", "pw")
+        op = Operation(kind="test.noop", user=user, username="hold_user", submission_key="k",
+                       resource="instance:u1", resource_label="c/vm")
+        claims.admit_job(op, {"compute:1": S, "instance:u1": X}, existing=lambda: None)
+        with claims.adopted(op):
+            with claims.hold({"compute:1": S, "instance:u1": X}):
+                pass
+        with self.assertRaises(claims.Busy):
+            with claims.hold({"instance:u1": X}):
+                pass