improve lock mechanisms

package/archlinux/ahriman.tmpfiles

@@ -1 +1,2 @@
 d /var/lib/ahriman 0755 ahriman ahriman
+d /run/ahriman 0755 ahriman ahriman

src/ahriman/application/ahriman.py

@@ -19,7 +19,6 @@
 #
 # pylint: disable=too-many-lines
 import argparse
-import tempfile
 
 from pathlib import Path
 from typing import TypeVar
@@ -73,8 +72,7 @@ def _parser() -> argparse.ArgumentParser:
     parser.add_argument("-c", "--configuration", help="configuration path", type=Path,
                         default=Path("/") / "etc" / "ahriman.ini")
     parser.add_argument("--force", help="force run, remove file lock", action="store_true")
-    parser.add_argument("-l", "--lock", help="lock file", type=Path,
+    parser.add_argument("-l", "--lock", help="lock file", type=Path, default=Path("ahriman.pid"))
-                        default=Path(tempfile.gettempdir()) / "ahriman.lock")
     parser.add_argument("--log-handler", help="explicit log handler specification. If none set, the handler will be "
                                               "guessed from environment",
                         type=LogHandler, choices=enum_values(LogHandler))
@@ -628,8 +626,7 @@ def _set_repo_daemon_parser(root: SubParserAction) -> argparse.ArgumentParser:
     parser.add_argument("-y", "--refresh", help="download fresh package databases from the mirror before actions, "
                                                 "-yy to force refresh even if up to date",
                         action="count", default=False)
-    parser.set_defaults(handler=handlers.Daemon, exit_code=False,
+    parser.set_defaults(handler=handlers.Daemon, exit_code=False, lock=Path("ahriman-daemon.pid"), package=[])
-                        lock=Path(tempfile.gettempdir()) / "ahriman-daemon.lock", package=[])
     return parser
 
 
@@ -880,7 +877,7 @@ def _set_service_clean_parser(root: SubParserAction) -> argparse.ArgumentParser:
                         action=argparse.BooleanOptionalAction, default=False)
     parser.add_argument("--pacman", help="clear directory with pacman local database cache",
                         action=argparse.BooleanOptionalAction, default=False)
-    parser.set_defaults(handler=handlers.Clean, quiet=True, unsafe=True)
+    parser.set_defaults(handler=handlers.Clean, lock=None, quiet=True, unsafe=True)
     return parser
 
 
@@ -1139,8 +1136,8 @@ def _set_web_parser(root: SubParserAction) -> argparse.ArgumentParser:
         argparse.ArgumentParser: created argument parser
     """
     parser = root.add_parser("web", help="web server", description="start web server", formatter_class=_formatter)
-    parser.set_defaults(handler=handlers.Web, architecture="", lock=Path(tempfile.gettempdir()) / "ahriman-web.lock",
+    parser.set_defaults(handler=handlers.Web, architecture="", lock=Path("ahriman-web.pid"), report=False,
-                        report=False, repository="", parser=_parser)
+                        repository="", parser=_parser)
     return parser
 
 

src/ahriman/application/lock.py

@@ -18,7 +18,10 @@
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
 #
 import argparse
+import fcntl
+import os
 
+from io import TextIOWrapper
 from pathlib import Path
 from types import TracebackType
 from typing import Literal, Self
@@ -36,7 +39,7 @@ from ahriman.models.waiter import Waiter
 
 class Lock(LazyLogging):
     """
-    wrapper for application lock file
+    wrapper for application lock file. Credits for idea to https://github.com/bmhatfield/python-pidfile.git
 
     Attributes:
         force(bool): remove lock file on start if any
@@ -70,8 +73,13 @@ class Lock(LazyLogging):
             repository_id(RepositoryId): repository unique identifier
             configuration(Configuration): configuration instance
         """
-        self.path: Path | None = \
+        self.path: Path | None = None
-            args.lock.with_stem(f"{args.lock.stem}_{repository_id.id}") if args.lock is not None else None
+        if args.lock is not None:
+            self.path = args.lock.with_stem(f"{args.lock.stem}_{repository_id.id}")
+            if not self.path.is_absolute():
+                # prepend full path to the lock file
+                self.path = Path("/") / "run" / "ahriman" / self.path
+        self._pid_file: TextIOWrapper | None = None
 
         self.force: bool = args.force
         self.unsafe: bool = args.unsafe
@@ -80,6 +88,65 @@ class Lock(LazyLogging):
         self.paths = configuration.repository_paths
         self.reporter = Client.load(repository_id, configuration, report=args.report)
 
+    @staticmethod
+    def perform_lock(fd: int) -> bool:
+        """
+        perform file lock
+
+        Args:
+            fd(int): file descriptor:
+
+        Returns:
+            bool: True in case if file is locked and False otherwise
+        """
+        try:
+            fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
+        except OSError:
+            return False
+
+        return True
+
+    def _open(self) -> None:
+        """
+        create lock file
+        """
+        if self.path is None:
+            return
+        self._pid_file = self.path.open("a+")
+
+    def _watch(self) -> None:
+        """
+        watch until lock disappear
+        """
+        # there are reasons why we are not using inotify here. First of all, if we would use it, it would bring to
+        # race conditions because multiple processes will be notified at the same time. Secondly, it is good library,
+        # but platform-specific, and we only need to check if file exists
+        if self._pid_file is None:
+            return
+
+        waiter = Waiter(self.wait_timeout)
+        waiter.wait(self.perform_lock, self._pid_file.fileno())
+
+    def _write(self) -> None:
+        """
+        write pid to the lock file
+
+        Raises:
+            DuplicateRunError: if it cannot lock PID file
+        """
+        if self._pid_file is None:
+            return
+        if not self.perform_lock(self._pid_file.fileno()):
+            raise DuplicateRunError
+
+        self._pid_file.seek(0)  # reset bytes
+        self._pid_file.truncate()
+
+        self._pid_file.write(str(os.getpid()))  # write current pid
+        self._pid_file.flush()  # flush data to disk
+
+        self._pid_file.seek(0)  # reset position again
+
     def check_user(self) -> None:
         """
         check if current user is actually owner of ahriman root
@@ -100,46 +167,33 @@ class Lock(LazyLogging):
         """
         remove lock file
         """
-        if self.path is None:
+        if self._pid_file is not None:  # close file descriptor
-            return
+            try:
+                self._pid_file.close()
+            except IOError:
+                pass  # suppress any IO errors occur
+        if self.path is not None:  # remove lock file
             self.path.unlink(missing_ok=True)
 
-    def create(self) -> None:
+    def lock(self) -> None:
         """
-        create lock file
+        create pid file
-
-        Raises:
-            DuplicateRunError: if lock exists and no force flag supplied
         """
-        if self.path is None:
+        if self.force:  # remove lock if force flag is set
-            return
+            self.clear()
-        try:
+        self._open()
-            self.path.touch(exist_ok=self.force)
+        self._watch()
-        except FileExistsError:
+        self._write()
-            raise DuplicateRunError from None
-
-    def watch(self) -> None:
-        """
-        watch until lock disappear
-        """
-        # there are reasons why we are not using inotify here. First of all, if we would use it, it would bring to
-        # race conditions because multiple processes will be notified in the same time. Secondly, it is good library,
-        # but platform-specific, and we only need to check if file exists
-        if self.path is None:
-            return
-
-        waiter = Waiter(self.wait_timeout)
-        waiter.wait(self.path.is_file)
 
     def __enter__(self) -> Self:
         """
         default workflow is the following:
 
             #. Check user UID
-            #. Check if there is lock file
             #. Check web status watcher status
+            #. Open lock file
             #. Wait for lock file to be free
-            #. Create lock file and directory tree
+            #. Write current PID to the lock file
             #. Report to status page if enabled
 
         Returns:
@@ -147,8 +201,7 @@ class Lock(LazyLogging):
         """
         self.check_user()
         self.check_version()
-        self.watch()
+        self.lock()
-        self.create()
         self.reporter.status_update(BuildStatusEnum.Building)
         return self
 

tests/ahriman/application/test_ahriman.py

@@ -1097,9 +1097,10 @@ def test_subparsers_repo_update_option_refresh(parser: argparse.ArgumentParser)
 
 def test_subparsers_service_clean(parser: argparse.ArgumentParser) -> None:
     """
-    service-clean command must imply quiet and unsafe
+    service-clean command must imply lock, quiet and unsafe
     """
     args = parser.parse_args(["service-clean"])
+    assert args.lock is None
     assert args.quiet
     assert args.unsafe
 

tests/ahriman/application/test_lock.py

@@ -1,10 +1,12 @@
 import argparse
+import fcntl
+import os
 import pytest
-import tempfile
 
 from pathlib import Path
 from pytest_mock import MockerFixture
-from unittest.mock import call as MockCall
+from tempfile import NamedTemporaryFile
+from unittest.mock import MagicMock, call as MockCall
 
 from ahriman import __version__
 from ahriman.application.lock import Lock
@@ -22,14 +24,102 @@ def test_path(args: argparse.Namespace, configuration: Configuration) -> None:
 
     assert Lock(args, repository_id, configuration).path is None
 
-    args.lock = Path("/run/ahriman.lock")
+    args.lock = Path("/run/ahriman.pid")
-    assert Lock(args, repository_id, configuration).path == Path("/run/ahriman_x86_64-aur-clone.lock")
+    assert Lock(args, repository_id, configuration).path == Path("/run/ahriman_x86_64-aur-clone.pid")
+
+    args.lock = Path("ahriman.pid")
+    assert Lock(args, repository_id, configuration).path == Path("/run/ahriman/ahriman_x86_64-aur-clone.pid")
 
     with pytest.raises(ValueError):
         args.lock = Path("/")
         assert Lock(args, repository_id, configuration).path  # special case
 
 
+def test_perform_lock(mocker: MockerFixture) -> None:
+    """
+    must lock file with fcntl
+    """
+    flock_mock = mocker.patch("fcntl.flock")
+    assert Lock.perform_lock(1)
+    flock_mock.assert_called_once_with(1, fcntl.LOCK_EX | fcntl.LOCK_NB)
+
+
+def test_perform_lock_exception(mocker: MockerFixture) -> None:
+    """
+    must return False on OSError
+    """
+    mocker.patch("fcntl.flock", side_effect=OSError)
+    assert not Lock.perform_lock(1)
+
+
+def test_open(lock: Lock, mocker: MockerFixture) -> None:
+    """
+    must open file
+    """
+    open_mock = mocker.patch("pathlib.Path.open")
+    lock.path = Path("ahriman.pid")
+
+    lock._open()
+    open_mock.assert_called_once_with("a+")
+
+
+def test_open_skip(lock: Lock, mocker: MockerFixture) -> None:
+    """
+    must skip file opening if path is not set
+    """
+    open_mock = mocker.patch("pathlib.Path.open")
+    lock._open()
+    open_mock.assert_not_called()
+
+
+def test_watch(lock: Lock, mocker: MockerFixture) -> None:
+    """
+    must check if lock file exists
+    """
+    lock._pid_file = MagicMock()
+    lock._pid_file.fileno.return_value = 1
+    wait_mock = mocker.patch("ahriman.models.waiter.Waiter.wait")
+
+    lock._watch()
+    wait_mock.assert_called_once_with(lock.perform_lock, 1)
+
+
+def test_watch_skip(lock: Lock, mocker: MockerFixture) -> None:
+    """
+    must skip watch on empty path
+    """
+    mocker.patch("ahriman.application.lock.Lock.perform_lock", return_value=True)
+    lock._watch()
+
+
+def test_write(lock: Lock) -> None:
+    """
+    must write PID to lock file
+    """
+    with NamedTemporaryFile("a+") as pid_file:
+        lock._pid_file = pid_file
+        lock._write()
+
+        assert int(lock._pid_file.readline()) == os.getpid()
+
+
+def test_write_skip(lock: Lock) -> None:
+    """
+    must skip write to file if no path set
+    """
+    lock._write()
+
+
+def test_write_locked(lock: Lock, mocker: MockerFixture) -> None:
+    """
+    must raise DuplicateRunError if cannot lock file
+    """
+    mocker.patch("ahriman.application.lock.Lock.perform_lock", return_value=False)
+    with pytest.raises(DuplicateRunError):
+        lock._pid_file = MagicMock()
+        lock._write()
+
+
 def test_check_user(lock: Lock, mocker: MockerFixture) -> None:
     """
     must check user correctly
@@ -88,7 +178,7 @@ def test_clear(lock: Lock) -> None:
     """
     must remove lock file
     """
-    lock.path = Path(tempfile.gettempdir()) / "ahriman-test.lock"
+    lock.path = Path("ahriman-test.pid")
     lock.path.touch()
 
     lock.clear()
@@ -99,7 +189,7 @@ def test_clear_missing(lock: Lock) -> None:
     """
     must not fail on lock removal if file is missing
     """
-    lock.path = Path(tempfile.gettempdir()) / "ahriman-test.lock"
+    lock.path = Path("ahriman-test.pid")
     lock.clear()
 
 
@@ -112,67 +202,52 @@ def test_clear_skip(lock: Lock, mocker: MockerFixture) -> None:
     unlink_mock.assert_not_called()
 
 
-def test_create(lock: Lock) -> None:
+def test_clear_close(lock: Lock) -> None:
     """
-    must create lock
+    must close pid file if opened
     """
-    lock.path = Path(tempfile.gettempdir()) / "ahriman-test.lock"
+    close_mock = lock._pid_file = MagicMock()
-
+    lock.clear()
-    lock.create()
+    close_mock.close.assert_called_once_with()
-    assert lock.path.is_file()
-    lock.path.unlink()
 
 
-def test_create_exception(lock: Lock) -> None:
+def test_clear_close_exception(lock: Lock) -> None:
     """
-    must raise exception if file already exists
+    must suppress IO exception on file closure
     """
-    lock.path = Path(tempfile.gettempdir()) / "ahriman-test.lock"
+    close_mock = lock._pid_file = MagicMock()
-    lock.path.touch()
+    close_mock.close.side_effect = IOError()
-
+    lock.clear()
-    with pytest.raises(DuplicateRunError):
-        lock.create()
-    lock.path.unlink()
 
 
-def test_create_skip(lock: Lock, mocker: MockerFixture) -> None:
+def test_lock(lock: Lock, mocker: MockerFixture) -> None:
     """
-    must skip creating if no file set
+    must perform lock correctly
     """
-    touch_mock = mocker.patch("pathlib.Path.touch")
+    clear_mock = mocker.patch("ahriman.application.lock.Lock.clear")
-    lock.create()
+    open_mock = mocker.patch("ahriman.application.lock.Lock._open")
-    touch_mock.assert_not_called()
+    watch_mock = mocker.patch("ahriman.application.lock.Lock._watch")
+    write_mock = mocker.patch("ahriman.application.lock.Lock._write")
+
+    lock.lock()
+    clear_mock.assert_not_called()
+    open_mock.assert_called_once_with()
+    watch_mock.assert_called_once_with()
+    write_mock.assert_called_once_with()
 
 
-def test_create_unsafe(lock: Lock) -> None:
+def test_lock_clear(lock: Lock, mocker: MockerFixture) -> None:
     """
-    must not raise exception if force flag set
+    must clear lock file before lock if force flag is set
     """
+    mocker.patch("ahriman.application.lock.Lock._open")
+    mocker.patch("ahriman.application.lock.Lock._watch")
+    mocker.patch("ahriman.application.lock.Lock._write")
+    clear_mock = mocker.patch("ahriman.application.lock.Lock.clear")
     lock.force = True
-    lock.path = Path(tempfile.gettempdir()) / "ahriman-test.lock"
-    lock.path.touch()
 
-    lock.create()
+    lock.lock()
-    lock.path.unlink()
+    clear_mock.assert_called_once_with()
-
-
-def test_watch(lock: Lock, mocker: MockerFixture) -> None:
-    """
-    must check if lock file exists
-    """
-    wait_mock = mocker.patch("ahriman.models.waiter.Waiter.wait")
-    lock.path = Path(tempfile.gettempdir()) / "ahriman-test.lock"
-
-    lock.watch()
-    wait_mock.assert_called_once_with(lock.path.is_file)
-
-
-def test_watch_skip(lock: Lock, mocker: MockerFixture) -> None:
-    """
-    must skip watch on empty path
-    """
-    mocker.patch("pathlib.Path.is_file", return_value=True)
-    lock.watch()
 
 
 def test_enter(lock: Lock, mocker: MockerFixture) -> None:
@@ -181,18 +256,14 @@ def test_enter(lock: Lock, mocker: MockerFixture) -> None:
     """
     check_user_mock = mocker.patch("ahriman.application.lock.Lock.check_user")
     check_version_mock = mocker.patch("ahriman.application.lock.Lock.check_version")
-    watch_mock = mocker.patch("ahriman.application.lock.Lock.watch")
+    lock_mock = mocker.patch("ahriman.application.lock.Lock.lock")
-    clear_mock = mocker.patch("ahriman.application.lock.Lock.clear")
-    create_mock = mocker.patch("ahriman.application.lock.Lock.create")
     update_status_mock = mocker.patch("ahriman.core.status.Client.status_update")
 
     with lock:
         pass
     check_user_mock.assert_called_once_with()
-    clear_mock.assert_called_once_with()
-    create_mock.assert_called_once_with()
     check_version_mock.assert_called_once_with()
-    watch_mock.assert_called_once_with()
+    lock_mock.assert_called_once_with()
     update_status_mock.assert_has_calls([MockCall(BuildStatusEnum.Building), MockCall(BuildStatusEnum.Success)])
 
 
@@ -202,7 +273,7 @@ def test_exit_with_exception(lock: Lock, mocker: MockerFixture) -> None:
     """
     mocker.patch("ahriman.application.lock.Lock.check_user")
     mocker.patch("ahriman.application.lock.Lock.clear")
-    mocker.patch("ahriman.application.lock.Lock.create")
+    mocker.patch("ahriman.application.lock.Lock.lock")
     update_status_mock = mocker.patch("ahriman.core.status.Client.status_update")
 
     with pytest.raises(ValueError):