Add seconds to engine program id generation (#3906)

- Clients were occasionally getting duplicate program ids
when running successive results.
- Root cause is unknown, but likely cause is that a sub-module
was calling random.seed() somewhere.
- This changes program id generation to include seconds in the id,
so that successive calls will generate distinct ids even if the
random number generator is seeded.

Co-authored-by: Cirq Bot <craiggidney+github+cirqbot@google.com>

cirq/google/engine/engine.py

@@ -65,7 +65,7 @@ class ProtoVersion(enum.Enum):
 def _make_random_id(prefix: str, length: int = 16):
     random_digits = [random.choice(string.ascii_uppercase + string.digits) for _ in range(length)]
     suffix = ''.join(random_digits)
-    suffix += datetime.date.today().strftime('%y%m%d')
+    suffix += datetime.date.today().strftime('%y%m%d-%H%M%S')
     return f'{prefix}{suffix}'
 
 

cirq/google/engine/engine_test.py

@@ -15,6 +15,7 @@
 """Tests for engine."""
 import os
 from unittest import mock
+import time
 import numpy as np
 import pytest
 
@@ -264,6 +265,17 @@ def _to_timestamp(json_string):
 )
 
 
+def test_make_random_id():
+    with mock.patch('random.choice', return_value='A'):
+        random_id = cg.engine.engine._make_random_id('prefix-', length=4)
+        assert random_id[:11] == 'prefix-AAAA'
+    random_id = cg.engine.engine._make_random_id('prefix-')
+    time.sleep(1)
+    random_id2 = cg.engine.engine._make_random_id('prefix-')
+    # Verify program id generate distinct even if random is seeded
+    assert random_id != random_id2
+
+
 @pytest.fixture(scope='session', autouse=True)
 def mock_grpc_client():
     with mock.patch(