Add a comment and tests to @catch_db_is_corrupted_exception decorator

src/tribler/core/upgrade/tests/test_upgrader.py

@@ -3,7 +3,7 @@
 import time
 from pathlib import Path
 from typing import Set
-from unittest.mock import patch
+from unittest.mock import Mock, patch
 
 import pytest
 from ipv8.keyvault.private.libnaclkey import LibNaCLSK
@@ -15,8 +15,10 @@
 from tribler.core.tests.tools.common import TESTS_DATA_DIR
 from tribler.core.upgrade.db8_to_db10 import calc_progress
 from tribler.core.upgrade.tags_to_knowledge.tags_db import TagDatabase
-from tribler.core.upgrade.upgrade import TriblerUpgrader, cleanup_noncompliant_channel_torrents
+from tribler.core.upgrade.upgrade import TriblerUpgrader, catch_db_is_corrupted_exception, \
+    cleanup_noncompliant_channel_torrents
 from tribler.core.utilities.configparser import CallbackConfigParser
+from tribler.core.utilities.pony_utils import DatabaseIsCorrupted
 from tribler.core.utilities.utilities import random_infohash
 
 
@@ -55,6 +57,35 @@ def _copy(source_name, target):
     shutil.copyfile(source, target)
 
 
+def test_catch_db_is_corrupted_exception_with_exception():
+    upgrader = Mock(_db_is_corrupted_exception=None)
+    upgrader_method = Mock(side_effect=DatabaseIsCorrupted())
+    decorated_method = catch_db_is_corrupted_exception(upgrader_method)
+
+    # Call the decorated method and expect it to catch the exception
+    decorated_method(upgrader)
+    upgrader_method.assert_called_once()
+
+    # Check if the exception was caught and stored
+    upgrader_method.assert_called_once()
+    assert isinstance(upgrader._db_is_corrupted_exception, DatabaseIsCorrupted)
+    upgrader._logger.exception.assert_called_once()
+
+
+def test_catch_db_is_corrupted_exception_without_exception():
+    upgrader = Mock(_db_is_corrupted_exception=None)
+    upgrader_method = Mock()
+    decorated_method = catch_db_is_corrupted_exception(upgrader_method)
+
+    # Call the decorated method and expect it to run without exceptions
+    decorated_method(upgrader)
+
+    # Check if the method was called and no exception was stored
+    upgrader_method.assert_called_once()
+    assert upgrader._db_is_corrupted_exception is None
+    upgrader._logger.exception.assert_not_called()
+
+
 def test_upgrade_pony_db_complete(upgrader, channels_dir, state_dir, trustchain_keypair,
                                   mds_path):  # pylint: disable=W0621
     """

src/tribler/core/upgrade/upgrade.py

@@ -71,6 +71,19 @@ def cleanup_noncompliant_channel_torrents(state_dir):
 
 
 def catch_db_is_corrupted_exception(upgrader_method):
+    # This decorator applied for TriblerUpgrader methods. It suppresses and remembers the DatabaseIsCorrupted exception.
+    # As a result, if one upgrade method raises an exception, the following upgrade methods are still executed.
+
+    # The reason for this is the following: it is possible that one upgrade methods upgrades a database A, while
+    # the next upgrade method upgrades a database B. If a corruption detected in the database A, the database B still
+    # need to be upgraded. So we want to temporarily suppress DatabaseIsCorrupted exception until all upgrades are
+    # executed.
+
+    # If an upgrade found the database to be corrupted, the database is marked as corrupted. Then, the next upgrade
+    # will rename the corrupted database file (this is handled by the get_db_version call) and immediately return
+    # because there is no database to upgrade. So, if one upgrade function detects the database corruption, all the
+    # following upgrade functions for this specific database will skip the actual upgrade. As a result, a new
+    # database with the current DB version will be created on the Tribler Core start.
 
     @wraps(upgrader_method)
     def new_method(*args, **kwargs):
@@ -81,7 +94,7 @@ def new_method(*args, **kwargs):
             self._logger.exception(exc)
 
             if not self._db_is_corrupted_exception:
-                self._db_is_corrupted_exception = exc
+                self._db_is_corrupted_exception = exc  # Suppress and remember the exception to re-raise it later
 
     return new_method
 
@@ -125,6 +138,9 @@ def run(self):
         self.upgrade_pony_db_14to15()
 
         if self._db_is_corrupted_exception:
+            # The current code is executed in the worker's thread. After all upgrade methods are executed,
+            # we re-raise the delayed exception, and then it is received and handled in the main thread
+            # by the UpgradeManager.on_worker_finished signal handler.
             raise self._db_is_corrupted_exception  # pylint: disable=raising-bad-type
 
     def remove_old_logs(self) -> Tuple[List[Path], List[Path]]: