Allow autosave backups to be overwritten without timestamps

fix docs

docs/examples/example_autosave_ioc.py

@@ -7,13 +7,13 @@
 # Create records, set some of them to autosave, also save some of their fields
 
 builder.aOut("AO", autosave=True)
-builder.aIn("AI", autosave_fields=["PREC", "SCAN"])
+builder.aIn("AI", autosave_fields=["PREC", "EGU"])
 builder.boolIn("BO")
 builder.WaveformIn("WAVEFORMOUT", [0, 0, 0, 0], autosave=True)
 minutes = builder.longOut("MINUTESRUN", autosave=True)
 
 autosave.configure(
-    directory="/tmp/autosave-data/MY-DEVICE-PREFIX",
+    directory="/tmp/autosave-data",
     name="MY-DEVICE-PREFIX",
     save_period=20.0
 )

docs/how-to/use-autosave-in-an-ioc.rst

@@ -26,7 +26,7 @@ Autosave is disabled by default until `autosave.configure()` is called. The firs
 set to 30.0 by default. The directory must exist, and should be configured with the appropriate
 read/write permissions for the user running the IOC.
 
-IOC developers should only need to interface with autosave via the `autosave.configre()`
+IOC developers should only need to interface with autosave via the `autosave.configure()`
 method and the ``autosave`` and ``autosave_fields`` keyword arguments,
 all other module members are intended for internal use only.
 
@@ -38,18 +38,19 @@ Users are discouraged from manually editing the backup files while the
 IOC is running so that the internal state of the autosave thread is consistent with
 the backup file.
 
-If autosave is enabled and active, a timestamped backup file of the latest existing backup file is created
-when the IOC is restarted, e.g. ``<name>.softsave-240717-095004`` (timestamps are in the format yymmdd-HHMMSS).
-This can be disabled by passing ``backup_on_load=False`` to `autosave.configure()`.
-To disable any autosaving, comment out the `autosave.configre()` call or pass it the keyword argument
+If autosave is enabled and active, a timestamped copy of the latest existing autosave backup file is created
+when the IOC is restarted, e.g. ``<name>.softsav_240717-095004`` (timestamps are in the format yymmdd-HHMMSS).
+If you only wish to store one backup of the autosave file at a time, ``timestamped_backups=False`` can be passed to `autosave.configure()`,
+this will create a backup file named ``<name>.softsav.bu``.
+To disable any autosaving, comment out the `autosave.configure()` call or pass it the keyword argument
 ``enabled=False``.
 
 The resulting backup file after running the IOC for a minute is the following:
 
 .. code-block::
 
+    AI.EGU: ''
     AI.PREC: '0'
-    AI.SCAN: I/O Intr
     AO: 0.0
     MINUTESRUN: 1
     WAVEFORMOUT: [0, 0, 0, 0]

softioc/autosave.py

@@ -22,7 +22,11 @@ def _ndarray_representer(dumper, array):
 
 
 def configure(
-    directory, name, save_period=DEFAULT_SAVE_PERIOD, backup=True, enabled=True
+    directory,
+    name,
+    save_period=DEFAULT_SAVE_PERIOD,
+    timestamped_backups=True,
+    enabled=True
 ):
     """This should be called before initialising the IOC. Configures the
     autosave thread for periodic backing up of PV values.
@@ -34,13 +38,14 @@ def configure(
             is usually the same as the device prefix.
         save_period: time in seconds between backups. Backups are only performed
             if PV values have changed.
-        backup: creates a backup of the loaded autosave file on load,
-            timestamped with the time of backup.
+        timestamped_backups: boolean which determines if backups of existing
+            autosave files are timestamped on IOC restart. True by default, if
+            False then backups get overwritten on each IOC restart.
         enabled: boolean which enables or disables autosave, set to True by
             default, or False if configure not called.
     """
     Autosave.directory = Path(directory)
-    Autosave.backup_on_load = backup
+    Autosave.timestamped_backups = timestamped_backups
     Autosave.save_period = save_period
     Autosave.enabled = enabled
     Autosave.device_name = name
@@ -103,7 +108,7 @@ class Autosave:
     device_name = None
     directory = None
     enabled = False
-    backup_on_load = False
+    timestamped_backups = True
 
     def __init__(self):
         if not self.enabled:
@@ -129,39 +134,48 @@ def __init__(self):
         self._last_saved_time = datetime.now()
 
     @classmethod
-    def _backup_sav_file(cls):
+    def __backup_sav_file(cls):
         if not cls.directory and cls.directory.is_dir():
             print(
                 f"Could not back up autosave as {cls.directory} is"
                 " not a valid directory",
                 file=sys.stderr,
             )
             return
-        sav_path = cls._get_current_sav_path()
+        sav_path = cls.__get_current_sav_path()
+        if cls.timestamped_backups:
+            backup_path = cls.__get_timestamped_backup_sav_path()
+        else:
+            backup_path = cls.__get_backup_sav_path()
         if sav_path.is_file():
-            copy2(sav_path, cls._get_timestamped_backup_sav_path())
+            copy2(sav_path, backup_path)
         else:
             print(
                 f"Could not back up autosave, {sav_path} is not a file",
                 file=sys.stderr,
             )
 
     @classmethod
-    def _get_timestamped_backup_sav_path(cls):
-        sav_path = cls._get_current_sav_path()
+    def __get_timestamped_backup_sav_path(cls):
+        sav_path = cls.__get_current_sav_path()
         return sav_path.parent / (
             sav_path.name + cls._last_saved_time.strftime("_%y%m%d-%H%M%S")
         )
 
     @classmethod
-    def _get_backup_sav_path(cls):
+    def __get_backup_sav_path(cls):
+        sav_path = cls.__get_current_sav_path()
+        return sav_path.parent / (sav_path.name + ".bu")
+
+    @classmethod
+    def __get_tmp_sav_path(cls):
         return cls.directory / f"{cls.device_name}.{SAVB_SUFFIX}"
 
     @classmethod
-    def _get_current_sav_path(cls):
+    def __get_current_sav_path(cls):
         return cls.directory / f"{cls.device_name}.{SAV_SUFFIX}"
 
-    def _get_state(self):
+    def __get_state(self):
         state = {}
         for pv_field, pv in self._pvs.items():
             try:
@@ -172,7 +186,7 @@ def _get_state(self):
         return state
 
     @classmethod
-    def _set_pvs_from_saved_state(cls):
+    def __set_pvs_from_saved_state(cls):
         for pv_field, value in cls._last_saved_state.items():
             try:
                 pv = cls._pvs[pv_field]
@@ -184,33 +198,32 @@ def _set_pvs_from_saved_state(cls):
                 )
                 traceback.print_exc()
 
-    def _state_changed(self, state):
+    def __state_changed(self, state):
         return self._last_saved_state.keys() != state.keys() or any(
             # checks equality for builtins and numpy arrays
             not numpy.array_equal(state[key], self._last_saved_state[key])
             for key in state
         )
 
     def _save(self):
-        state = self._get_state()
-        if self._state_changed(state):
-            sav_path = self._get_current_sav_path()
-            backup_path = self._get_backup_sav_path()
-            # write to backup file first then use atomic os.rename
+        state = self.__get_state()
+        if self.__state_changed(state):
+            sav_path = self.__get_current_sav_path()
+            tmp_path = self.__get_tmp_sav_path()
+            # write to temporary file first then use atomic os.rename
             # to safely update stored state
-            with open(backup_path, "w") as backup:
+            with open(tmp_path, "w") as backup:
                 yaml.dump(state, backup, indent=4)
-            rename(backup_path, sav_path)
+            rename(tmp_path, sav_path)
             self._last_saved_state = state
             self._last_saved_time = datetime.now()
 
     @classmethod
     def _load(cls, path=None):
         if not cls.enabled or not cls._pvs:
             return
-        if cls.backup_on_load:
-            cls._backup_sav_file()
-        sav_path = path or cls._get_current_sav_path()
+        cls.__backup_sav_file()
+        sav_path = path or cls.__get_current_sav_path()
         if not sav_path or not sav_path.is_file():
             print(
                 f"Could not load autosave values from file {sav_path}",
@@ -219,7 +232,7 @@ def _load(cls, path=None):
             return
         with open(sav_path, "r") as f:
             cls._last_saved_state = yaml.full_load(f)
-        cls._set_pvs_from_saved_state()
+        cls.__set_pvs_from_saved_state()
 
     def stop(self):
         self._stop_event.set()

tests/test_autosave.py

@@ -19,7 +19,7 @@ def reset_autosave_setup_teardown():
     default_device_name = autosave.Autosave.device_name
     default_directory = autosave.Autosave.directory
     default_enabled = autosave.Autosave.enabled
-    default_bol = autosave.Autosave.backup_on_load
+    default_tb = autosave.Autosave.timestamped_backups
     yield
     autosave.Autosave._pvs = default_pvs
     autosave.Autosave._last_saved_state = default_state
@@ -28,7 +28,7 @@ def reset_autosave_setup_teardown():
     autosave.Autosave.device_name = default_device_name
     autosave.Autosave.directory = default_directory
     autosave.Autosave.enabled = default_enabled
-    autosave.Autosave.backup_on_load = default_bol
+    autosave.Autosave.timestamped_backups = default_tb
     if builder.GetRecordNames().prefix:  # reset device name to empty if set
         builder.SetDeviceName("")
 
@@ -58,6 +58,8 @@ def existing_autosave_dir(tmp_path):
     }
     with open(tmp_path / f"{DEVICE_NAME}.softsav", "w") as f:
         yaml.dump(state, f, indent=4)
+    with open(tmp_path / f"{DEVICE_NAME}.softsav.bu", "w") as f:
+        yaml.dump({"OUT-OF-DATE-KEY": "out of date value"}, f, indent=4)
     return tmp_path
 
 
@@ -78,7 +80,7 @@ def test_autosave_defaults():
     assert autosave.Autosave.device_name is None
     assert autosave.Autosave.directory is None
     assert autosave.Autosave.enabled is False
-    assert autosave.Autosave.backup_on_load is False
+    assert autosave.Autosave.timestamped_backups is True
 
 
 def test_configure_dir_doesnt_exist(tmp_path):
@@ -177,19 +179,29 @@ def test_stop_event(tmp_path):
         worker.join(timeout=1)
 
 
-def test_backup_on_load(existing_autosave_dir):
-    autosave.configure(existing_autosave_dir, DEVICE_NAME, backup=True)
+@pytest.mark.parametrize(
+        "timestamped,regex",
+        [(False, r"^" + DEVICE_NAME + r"\.softsav_[0-9]{6}-[0-9]{6}$"),
+         (True, r"^" + DEVICE_NAME + r"\.softsav\.bu$")]
+    )
+def test_backup_on_load(existing_autosave_dir, timestamped, regex):
+    autosave.configure(
+        existing_autosave_dir,
+        DEVICE_NAME,
+        timestamped_backups=timestamped
+    )
     # backup only performed if there are any pvs to save
     builder.aOut("SAVED-AO", autosave=True)
     autosave.load_autosave()
     backup_files = list(existing_autosave_dir.glob("*.softsav_*"))
-    assert len(backup_files) == 1
-    # assert backup file is named <name>.softsave_yymmdd-HHMMSS
-    for file in backup_files:
-        assert re.match(
-            r"^" + DEVICE_NAME + r"\.softsav_[0-9]{6}-[0-9]{6}$", file.name
-        )
-
+    # assert backup is <name>.softsav_yymmdd-HHMMSS or <name>.softsav.bu
+    any(re.match(regex, file.name) for file in backup_files)
+    if not timestamped:
+        # test that existing .bu file gets overwritten
+        with open(existing_autosave_dir / f"{DEVICE_NAME}.softsav.bu") as f:
+            state = yaml.full_load(f)
+            assert "OUT-OF-DATE-KEY" not in state
+            assert "SAVED-AO" in state
 
 def test_autosave_key_names(tmp_path):
     builder.aOut("DEFAULTNAME", autosave=True)
@@ -206,7 +218,7 @@ def test_autosave_key_names(tmp_path):
 
 def check_all_record_types_load_properly(device_name, autosave_dir, conn):
     builder.SetDeviceName(device_name)
-    autosave.configure(autosave_dir, device_name, backup=False)
+    autosave.configure(autosave_dir, device_name)
     pv_aOut = builder.aOut("SAVED-AO", autosave=True)
     pv_aIn = builder.aIn("SAVED-AI", autosave=True)
     pv_boolOut = builder.boolOut("SAVED-BO", autosave=True)