1.0rc3: LineRequest

docs/source/conf.py

@@ -9,7 +9,7 @@
 project = 'ptvp35'
 copyright = '2022, PARRRATE TNV'
 author = 'PARRRATE TNV'
-release = '1.0rc2'
+release = '1.0rc3'
 
 # -- General configuration ---------------------------------------------------
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#general-configuration

docs/source/guarantees.rst

@@ -0,0 +1,36 @@
+Guarantees
+==========
+
+MMDB-level guarantees
+---------------
+
+* All 0L writes change MMDB instantly.
+* Transaction write works as one atomic write.
+
+Queue-level guarantees
+----------------------
+
+This level is the mediator between MMDB and filesystem levels. This level includes the pre-write compression buffer.
+
+* Queue requests occur in the same orders as they were acted upon at MMDB level and in the same order as they will be acted upon at filesystem level.
+* DB can't close until all requests are done.
+* No request can crash the task.
+* Every request eventually succeedes or fails (except for the case of runtime termination).
+
+Buffer-specific guarantees:
+
+* If buffer dump was ever requested, then this request (queued or indirect) will eventually be satisfied.
+
+Filesystem-level guarantees
+---------------------------
+
+* If main file exists without .recover or .truncate_flag, then it's valid.
+* If .recover file is present, then .backup is valid.
+* If .truncate_flag is present, then .truncate is valid and first :code:`.truncate_target()` (contents of .truncate) characters of main file are valid.
+* Every write is final and irreversible (can't be reversed unintentionally due to termination), otherwise it's not considered done. That's achieved using :code:`os.fsync`.
+
+Performance guarantees
+----------------------
+
+* No normal sync methods (except for :code:`io2db`/:code:`db2io` if they're supplied with blocking :code:`IO`) block on IO. Other methods are explicitly marked with postfix :code:`_sync`.
+* All requests are resolved as soon as their conditions are met.

docs/source/index.rst

@@ -1,8 +1,3 @@
-.. ptvp35 documentation master file, created by
-   sphinx-quickstart on Sat Nov 19 20:02:24 2022.
-   You can adapt this file completely to your liking, but it should at least
-   contain the root `toctree` directive.
-
 Welcome to ptvp35's documentation!
 ==================================
 
@@ -12,6 +7,7 @@ Welcome to ptvp35's documentation!
    motivation
    usage
    modules
+   guarantees
 
 
 
@@ -20,6 +16,7 @@ Indices and tables
 
 * :doc:`motivation`
 * :doc:`usage`
+* :doc:`guarantees`
 * :ref:`genindex`
 * :ref:`modindex`
 * :ref:`search`

docs/source/motivation.rst

@@ -1,6 +1,8 @@
 Motivation
 ==========
 
+This page describes reasons for certain design decisions.
+
 General structure
 -----------------
 

ptvp35/__init__.py

@@ -16,7 +16,7 @@ __all__ = (
     'DbFactory',
     'Db',
     'Transaction',
-    'FallbackMapping',
+    'TransactionView',
 )
 
 
@@ -44,19 +44,38 @@ class Request:
             await self.__future
 
 
+class LineRequest(Request):
+    __slots__ = (
+        'line',
+    )
+
+    def __init__(self, line: str, /, *, future: Optional[asyncio.Future]) -> None:
+        super().__init__(future)
+        self.line = line
+
+
 class KVFactory:
     """note: unstable signature."""
 
     __slots__ = ()
 
     def line(self, key: Any, value: Any, /) -> str:
-        """line must contain exactly one '\\n' at exactly the end if the line is not empty."""
+        """line must contain exactly one '\\n' at exactly the end if the line is not empty.
+note: other forms of requests will later be represented by different methods or by instances of Action class."""
         raise NotImplementedError
 
-    def fromline(self, line: str, /) -> 'KVRequest':
+    def fromline(self, line: str, /) -> tuple[Any, Any]:
-        """inverse of line(). should use free() method to construct the request."""
+        """inverse of line(). should use free() method to construct the request.
+note: unstable signature."""
         raise NotImplementedError
 
+    def run(self, line: str, db: dict, /) -> None:
+        """run request against the db.
+extensible to allow forms of requests other than set.
+note: unstable signature."""
+        key, value = self.fromline(line)
+        db[key] = value
+
     def request(self, key: Any, value: Any, /, *, future: Optional[asyncio.Future]) -> 'KVRequest':
         """form request with Future.
 low-level API.
@@ -69,7 +88,7 @@ note: unstable signature."""
         return self.request(key, value, future=None)
 
 
-class KVRequest(Request):
+class KVRequest(LineRequest):
     __slots__ = (
         '__factory',
         'key',
@@ -77,24 +96,18 @@ class KVRequest(Request):
     )
 
     def __init__(self, key: Any, value: Any, /, *, future: Optional[asyncio.Future], factory: KVFactory):
-        super().__init__(future)
+        super().__init__(factory.line(key, value), future=future)
         self.__factory = factory
         self.key = key
         self.value = value
 
-    def free(self, /):
-        return self.__factory.free(self.key, self.value)
-
-    def line(self, /) -> str:
-        return self.__factory.line(self.key, self.value)
-
 
 class DumpRequest(Request):
     __slots__ = ()
 
 
 class UnknownRequestType(TypeError):
-    pass
+    __slots__ = ()
 
 
 class KVJson(KVFactory):
@@ -118,23 +131,20 @@ class KVJson(KVFactory):
                 'unknown KVJson key type, cannot convert to hashable'
             )
 
-    def fromline(self, line: str, /) -> 'KVRequest':
+    def fromline(self, line: str, /) -> tuple[Any, Any]:
         d = json.loads(line)
-        return self.free(self._load_key(d['key']), d['value'])
+        return self._load_key(d['key']), d['value']
 
 
-class TransactionRequest(Request):
+class TransactionRequest(LineRequest):
     __slots__ = (
         'buffer',
     )
 
     def __init__(self, buffer: StringIO, /, *, future: Optional[asyncio.Future]):
-        super().__init__(future)
+        super().__init__(buffer.getvalue(), future=future)
         self.buffer = buffer
 
-    def line(self, /) -> str:
-        return self.buffer.getvalue()
-
 
 class DbConnection:
     """note: unstable constructor signature."""
@@ -208,8 +218,7 @@ note: unstable signature."""
         size = 0
         for line in io:
             try:
-                request = self.__factory.kvfactory.fromline(line)
+                self.__factory.kvfactory.run(line, db)
-                db[request.key] = request.value
                 size += len(line)
             except (json.JSONDecodeError, EOFError):
                 traceback.print_exc()
@@ -222,7 +231,7 @@ note: unstable signature."""
 note: unstable signature."""
         size = 0
         for key, value in db.items():
-            size += io.write(self.__factory.kvfactory.free(key, value).line())
+            size += io.write(self.__factory.kvfactory.line(key, value))
         return size
 
     def _path2db_sync(self, path: pathlib.Path, db: dict, /) -> int:
@@ -240,10 +249,10 @@ note: unstable signature."""
 
     async def set(self, key: Any, value: Any, /) -> None:
         """set the value and wait until it's written to disk."""
-        self.__mmdb[key] = value
         future = self._create_future()
-        self.__queue.put_nowait(
+        request = self.__factory.kvfactory.request(key, value, future=future)
-            self.__factory.kvfactory.request(key, value, future=future))
+        self.__mmdb[key] = value
+        self.__queue.put_nowait(request)
         await future
 
     def set_nowait(self, key: Any, value: Any, /) -> None:
@@ -352,13 +361,11 @@ note: unstable signature."""
             await self._reload()
 
     async def _handle_request(self, request: Request, /) -> None:
-        if isinstance(request, KVRequest):
+        if isinstance(request, LineRequest):
-            await self._write(request.line(), request)
+            await self._write(request.line, request)
         elif isinstance(request, DumpRequest):
             await self._dump_buffer()
             request.set_result(None)
-        elif isinstance(request, TransactionRequest):
-            await self._write(request.line(), request)
         else:
             raise UnknownRequestType
 
@@ -513,10 +520,11 @@ note: unstable signature."""
         future = self._create_future()
         self.__queue.put_nowait(TransactionRequest(buffer, future=future))
         await future
-    
+
-    def submit_transaction(self, delta: dict, /) -> asyncio.Future | None:
+    def submit_transaction(self, delta: dict, future: asyncio.Future | None, /) -> None:
         """not implemented.
-low-level API."""
+low-level API.
+note: unstable signature."""
         raise NotImplementedError
 
     async def commit(self, /) -> None:
@@ -575,7 +583,7 @@ class Db(DbConnection):
         await self.aclose()
 
 
-class FallbackMapping:
+class TransactionView:
     """note: unstable constructor signature."""
 
     __slots__ = (
@@ -620,7 +628,8 @@ bulk analog of DbConnection.set_nowait method."""
 
 
 class Transaction:
-    """note: unstable signature."""
+    """note: unstable signature.
+note: synchronous with is not implemented."""
 
     __slots__ = (
         '__connection',
@@ -632,11 +641,20 @@ class Transaction:
     def __init__(self, connection: DbConnection, /) -> None:
         self.__connection = connection
 
-    async def __aenter__(self) -> FallbackMapping:
+    async def __aenter__(self) -> TransactionView:
         self.__delta = {}
-        return FallbackMapping(self.__delta, self.__connection)
+        return TransactionView(self.__delta, self.__connection)
 
     async def __aexit__(self, exc_type, exc_val, exc_tb):
         if exc_type is None:
             await self.__connection.complete_transaction(self.__delta)
         del self.__delta
+
+    def __enter__(self) -> TransactionView:
+        self.__delta = {}
+        return TransactionView(self.__delta, self.__connection)
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        if exc_type is None:
+            self.__connection.submit_transaction(self.__delta, None)
+        del self.__delta

setup.py

@@ -2,7 +2,7 @@ from setuptools import setup
 
 setup(
     name='ptvp35',
-    version='1.0rc1',
+    version='1.0rc3',
     packages=['ptvp35'],
     url='https://gitea.ongoteam.net/PTV/ptvp35',
     license='',