bpo-27334: roll back transaction if sqlite3 context manager fails to commit (GH-26202)

Co-authored-by: Luca Citi
Co-authored-by: Berker Peksag <berker.peksag@gmail.com>

Lib/sqlite3/test/dbapi.py

@@ -22,11 +22,17 @@
 
 import contextlib
 import sqlite3 as sqlite
+import subprocess
 import sys
 import threading
 import unittest
 
-from test.support import check_disallow_instantiation, threading_helper, bigmemtest
+from test.support import (
+    bigmemtest,
+    check_disallow_instantiation,
+    threading_helper,
+    SHORT_TIMEOUT,
+)
 from test.support.os_helper import TESTFN, unlink
 
 
@@ -986,6 +992,77 @@ class SqliteOnConflictTests(unittest.TestCase):
         self.assertEqual(self.cu.fetchall(), [('Very different data!', 'foo')])
 
 
+class MultiprocessTests(unittest.TestCase):
+    CONNECTION_TIMEOUT = SHORT_TIMEOUT / 1000.  # Defaults to 30 ms
+
+    def tearDown(self):
+        unlink(TESTFN)
+
+    def test_ctx_mgr_rollback_if_commit_failed(self):
+        # bpo-27334: ctx manager does not rollback if commit fails
+        SCRIPT = f"""if 1:
+            import sqlite3
+            def wait():
+                print("started")
+                assert "database is locked" in input()
+
+            cx = sqlite3.connect("{TESTFN}", timeout={self.CONNECTION_TIMEOUT})
+            cx.create_function("wait", 0, wait)
+            with cx:
+                cx.execute("create table t(t)")
+            try:
+                # execute two transactions; both will try to lock the db
+                cx.executescript('''
+                    -- start a transaction and wait for parent
+                    begin transaction;
+                    select * from t;
+                    select wait();
+                    rollback;
+
+                    -- start a new transaction; would fail if parent holds lock
+                    begin transaction;
+                    select * from t;
+                    rollback;
+                ''')
+            finally:
+                cx.close()
+        """
+
+        # spawn child process
+        proc = subprocess.Popen(
+            [sys.executable, "-c", SCRIPT],
+            encoding="utf-8",
+            bufsize=0,
+            stdin=subprocess.PIPE,
+            stdout=subprocess.PIPE,
+        )
+        self.addCleanup(proc.communicate)
+
+        # wait for child process to start
+        self.assertEqual("started", proc.stdout.readline().strip())
+
+        cx = sqlite.connect(TESTFN, timeout=self.CONNECTION_TIMEOUT)
+        try:  # context manager should correctly release the db lock
+            with cx:
+                cx.execute("insert into t values('test')")
+        except sqlite.OperationalError as exc:
+            proc.stdin.write(str(exc))
+        else:
+            proc.stdin.write("no error")
+        finally:
+            cx.close()
+
+        # terminate child process
+        self.assertIsNone(proc.returncode)
+        try:
+            proc.communicate(input="end", timeout=SHORT_TIMEOUT)
+        except subprocess.TimeoutExpired:
+            proc.kill()
+            proc.communicate()
+            raise
+        self.assertEqual(proc.returncode, 0)
+
+
 def suite():
     tests = [
         ClosedConTests,
@@ -995,6 +1072,7 @@ def suite():
         CursorTests,
         ExtensionTests,
         ModuleTests,
+        MultiprocessTests,
         OpenTests,
         SqliteOnConflictTests,
         ThreadTests,