Defer external resources until process initialization

plugboard/connector/connector.py

@@ -17,6 +17,10 @@ class Connector(ABC, ExportMixin):
     def __init__(self, spec: ConnectorSpec, *args: _t.Any, **kwargs: _t.Any) -> None:
         self.spec: ConnectorSpec = spec
 
+    async def init(self) -> None:
+        """Acquire resources required by this connector."""
+        pass
+
     @abstractmethod
     async def connect_send(self) -> Channel:
         """Returns a `Channel` for sending messages."""

plugboard/connector/ray_channel.py

@@ -1,5 +1,6 @@
 """Provides `RayChannel` for use in cluster compute environments."""
 
+import asyncio
 import typing as _t
 
 from plugboard.connector.asyncio_channel import AsyncioChannel
@@ -26,7 +27,7 @@ def __init__(  # noqa: D417
         actor_options: _t.Optional[dict[str, _t.Any]] = None,
         **kwargs: _t.Any,
     ) -> None:
-        """Instantiates `RayChannel`.
+        """Instantiates `RayChannel` and creates its remote actor.
 
         Args:
             actor_options: Optional; Options to pass to the Ray actor. Defaults to {"num_cpus": 0}.
@@ -71,12 +72,21 @@ def __init__(self, *args: _t.Any, **kwargs: _t.Any) -> None:
         super().__init__(*args, **kwargs)
         if self.spec.mode != ConnectorMode.PIPELINE:
             raise ValueError("RayConnector only supports `PIPELINE` type connections.")
-        self._channel = RayChannel()
+        self._channel: _t.Optional[RayChannel] = None
+        self._init_lock = asyncio.Lock()
+
+    async def init(self) -> None:
+        """Create the channel and its remote actor when execution starts."""
+        async with self._init_lock:
+            if self._channel is None:
+                self._channel = RayChannel()
 
     async def connect_send(self) -> RayChannel:
         """Returns a `RayChannel` for sending messages."""
-        return self._channel
+        await self.init()
+        return _t.cast(RayChannel, self._channel)
 
     async def connect_recv(self) -> RayChannel:
         """Returns a `RayChannel` for receiving messages."""
-        return self._channel
+        await self.init()
+        return _t.cast(RayChannel, self._channel)

plugboard/connector/zmq_channel.py

@@ -105,6 +105,7 @@ def __init__(
         super().__init__(*args, **kwargs)
         self._zmq_address = zmq_address
         self._maxsize = maxsize
+        self._init_lock = asyncio.Lock()
 
     @abstractmethod
     async def connect_send(self) -> ZMQChannel:
@@ -124,23 +125,31 @@ def __init__(self, *args: _t.Any, **kwargs: _t.Any) -> None:
         super().__init__(*args, **kwargs)
         self._send_channel: _t.Optional[ZMQChannel] = None
         self._recv_channel: _t.Optional[ZMQChannel] = None
-
-        # Socket to receive sender address from sender
-        self._sender_rep_socket = create_socket(zmq.REP, [])
-        self._sender_rep_socket_port = self._sender_rep_socket.bind_to_random_port("tcp://*")
-        self._sender_rep_socket_addr = f"{self._zmq_address}:{self._sender_rep_socket_port}"
-        self._sender_req_lock = asyncio.Lock()
+        self._sender_rep_socket: _t.Optional[zmq_asyncio.Socket] = None
+        self._sender_rep_socket_addr: _t.Optional[str] = None
+        self._sender_req_lock: _t.Optional[asyncio.Lock] = None
         self._sender_addr: _t.Optional[str] = None
-
-        # Socket to send sender address to receiver
-        self._receiver_rep_socket = create_socket(zmq.REP, [])
-        self._receiver_rep_socket_port = self._receiver_rep_socket.bind_to_random_port("tcp://*")
-        self._receiver_rep_socket_addr = f"{self._zmq_address}:{self._receiver_rep_socket_port}"
-        self._receiver_req_lock = asyncio.Lock()
-
-        self._exchange_addr_task = asyncio.create_task(self._exchange_address())
-        _zmq_exchange_addr_tasks.add(self._exchange_addr_task)
-        self._exchange_addr_task.add_done_callback(_zmq_exchange_addr_tasks.discard)
+        self._receiver_rep_socket: _t.Optional[zmq_asyncio.Socket] = None
+        self._receiver_rep_socket_addr: _t.Optional[str] = None
+        self._receiver_req_lock: _t.Optional[asyncio.Lock] = None
+        self._exchange_addr_task: _t.Optional[asyncio.Task[None]] = None
+
+    async def init(self) -> None:
+        """Allocate address exchange sockets when execution starts."""
+        async with self._init_lock:
+            if self._sender_rep_socket_addr is not None:
+                return
+            self._sender_rep_socket = create_socket(zmq.REP, [])
+            sender_port = self._sender_rep_socket.bind_to_random_port("tcp://*")
+            self._sender_rep_socket_addr = f"{self._zmq_address}:{sender_port}"
+            self._sender_req_lock = asyncio.Lock()
+            self._receiver_rep_socket = create_socket(zmq.REP, [])
+            receiver_port = self._receiver_rep_socket.bind_to_random_port("tcp://*")
+            self._receiver_rep_socket_addr = f"{self._zmq_address}:{receiver_port}"
+            self._receiver_req_lock = asyncio.Lock()
+            self._exchange_addr_task = asyncio.create_task(self._exchange_address())
+            _zmq_exchange_addr_tasks.add(self._exchange_addr_task)
+            self._exchange_addr_task.add_done_callback(_zmq_exchange_addr_tasks.discard)
 
     def __getstate__(self) -> dict:
         state = self.__dict__.copy()
@@ -152,6 +161,7 @@ def __getstate__(self) -> dict:
             "_exchange_addr_task",
             "_send_channel",
             "_recv_channel",
+            "_init_lock",
         ):
             if attr in state:
                 del state[attr]
@@ -161,37 +171,53 @@ def __setstate__(self, state: dict) -> None:
         self.__dict__.update(state)
         self._send_channel = None
         self._recv_channel = None
+        self._init_lock = asyncio.Lock()
 
     async def _exchange_address(self) -> None:
+        if (
+            self._sender_req_lock is None
+            or self._sender_rep_socket is None
+            or self._receiver_req_lock is None
+            or self._receiver_rep_socket is None
+        ):
+            raise ChannelSetupError("ZMQ connector is not initialized")
+        sender_req_lock = self._sender_req_lock
+        sender_rep_socket = self._sender_rep_socket
+        receiver_req_lock = self._receiver_req_lock
+        receiver_rep_socket = self._receiver_rep_socket
+
         async def _handle_sender_requests() -> None:
-            async with self._sender_req_lock:
-                sender_request = await self._sender_rep_socket.recv_json()
+            async with sender_req_lock:
+                sender_request = await sender_rep_socket.recv_json()
                 if (sender_addr := sender_request.get("sender_address")) is None:
-                    await self._sender_rep_socket.send_json({"success": False})
+                    await sender_rep_socket.send_json({"success": False})
                 else:
                     self._sender_addr = sender_addr
-                await self._sender_rep_socket.send_json({"success": True})
+                await sender_rep_socket.send_json({"success": True})
 
                 while True:
-                    await self._sender_rep_socket.recv_json()
-                    await self._sender_rep_socket.send_json({"success": False})
+                    await sender_rep_socket.recv_json()
+                    await sender_rep_socket.send_json({"success": False})
 
         async def _handle_receiver_requests() -> None:
             while self._sender_addr is None:
                 await asyncio.sleep(0.5)
             while True:
-                async with self._receiver_req_lock:
-                    await self._receiver_rep_socket.recv()
-                    await self._receiver_rep_socket.send(self._sender_addr.encode())
+                async with receiver_req_lock:
+                    await receiver_rep_socket.recv()
+                    await receiver_rep_socket.send(self._sender_addr.encode())
 
         async with asyncio.TaskGroup() as tg:
             tg.create_task(_handle_sender_requests())
             tg.create_task(_handle_receiver_requests())
 
     async def connect_send(self) -> ZMQChannel:
         """Returns a `ZMQChannel` for sending messages."""
+        await self.init()
         if self._send_channel is not None:
             return self._send_channel
+        if self._sender_rep_socket_addr is None:
+            raise ChannelSetupError("ZMQ connector is not initialized")
         send_socket = create_socket(zmq.PUSH, [(zmq.SNDHWM, self._maxsize)])
         send_port = send_socket.bind_to_random_port("tcp://*")
         send_addr = f"{self._zmq_address}:{send_port}"
@@ -210,8 +236,11 @@ async def connect_send(self) -> ZMQChannel:
 
     async def connect_recv(self) -> ZMQChannel:
         """Returns a `ZMQChannel` for receiving messages."""
+        await self.init()
         if self._recv_channel is not None:
             return self._recv_channel
+        if self._receiver_rep_socket_addr is None:
+            raise ChannelSetupError("ZMQ connector is not initialized")
         recv_socket = create_socket(zmq.PULL, [(zmq.RCVHWM, self._maxsize)])
 
         receiver_req_socket = create_socket(zmq.REQ, [])
@@ -232,16 +261,28 @@ class _ZMQPubsubConnector(_ZMQConnector):
     def __init__(self, *args: _t.Any, **kwargs: _t.Any) -> None:
         super().__init__(*args, **kwargs)
         self._topic = str(self.spec.source)
-        self._xsub_socket = create_socket(zmq.XSUB, [(zmq.RCVHWM, self._maxsize)])
-        self._xsub_port = self._xsub_socket.bind_to_random_port("tcp://*")
-        self._xpub_socket = create_socket(zmq.XPUB, [(zmq.SNDHWM, self._maxsize)])
-        self._xpub_port = self._xpub_socket.bind_to_random_port("tcp://*")
-        self._poller = zmq_asyncio.Poller()
-        self._poller.register(self._xsub_socket, zmq.POLLIN)
-        self._poller.register(self._xpub_socket, zmq.POLLIN)
-        self._poll_task = asyncio.create_task(self._poll())
-        _zmq_proxy_tasks.add(self._poll_task)
-        self._poll_task.add_done_callback(_zmq_proxy_tasks.discard)
+        self._xsub_port: _t.Optional[int] = None
+        self._xpub_port: _t.Optional[int] = None
+        self._poller: _t.Optional[zmq_asyncio.Poller] = None
+        self._poll_task: _t.Optional[asyncio.Task[None]] = None
+        self._xsub_socket: _t.Optional[zmq_asyncio.Socket] = None
+        self._xpub_socket: _t.Optional[zmq_asyncio.Socket] = None
+
+    async def init(self) -> None:
+        """Allocate proxy sockets when execution starts."""
+        async with self._init_lock:
+            if self._xsub_port is not None:
+                return
+            self._xsub_socket = create_socket(zmq.XSUB, [(zmq.RCVHWM, self._maxsize)])
+            self._xsub_port = self._xsub_socket.bind_to_random_port("tcp://*")
+            self._xpub_socket = create_socket(zmq.XPUB, [(zmq.SNDHWM, self._maxsize)])
+            self._xpub_port = self._xpub_socket.bind_to_random_port("tcp://*")
+            self._poller = zmq_asyncio.Poller()
+            self._poller.register(self._xsub_socket, zmq.POLLIN)
+            self._poller.register(self._xpub_socket, zmq.POLLIN)
+            self._poll_task = asyncio.create_task(self._poll())
+            _zmq_proxy_tasks.add(self._poll_task)
+            self._poll_task.add_done_callback(_zmq_proxy_tasks.discard)
 
     def __getstate__(self) -> dict:
         state = self.__dict__.copy()
@@ -252,6 +293,8 @@ def __getstate__(self) -> dict:
         return state
 
     async def _poll(self) -> None:
+        if self._poller is None or self._xpub_socket is None or self._xsub_socket is None:
+            raise ChannelSetupError("ZMQ connector is not initialized")
         poll_fn, xps, xss = self._poller.poll, self._xpub_socket, self._xsub_socket
         try:
             while True:
@@ -266,13 +309,19 @@ async def _poll(self) -> None:
 
     async def connect_send(self) -> ZMQChannel:
         """Returns a `ZMQChannel` for sending pubsub messages."""
+        await self.init()
+        if self._xsub_port is None:
+            raise ChannelSetupError("ZMQ connector is not initialized")
         send_socket = create_socket(zmq.PUB, [(zmq.SNDHWM, self._maxsize)])
         send_socket.connect(f"{self._zmq_address}:{self._xsub_port}")
         await asyncio.sleep(0.1)  # Ensure connections established before first send. Better way?
         return ZMQChannel(send_socket=send_socket, topic=self._topic, maxsize=self._maxsize)
 
     async def connect_recv(self) -> ZMQChannel:
         """Returns a `ZMQChannel` for receiving pubsub messages."""
+        await self.init()
+        if self._xpub_port is None:
+            raise ChannelSetupError("ZMQ connector is not initialized")
         socket_opts: zmq_sockopts_t = [
             (zmq.RCVHWM, self._maxsize),
             (zmq.SUBSCRIBE, self._topic.encode("utf8")),
@@ -286,17 +335,24 @@ async def connect_recv(self) -> ZMQChannel:
 class _ZMQPubsubConnectorProxy(_ZMQConnector):
     """`_ZMQPubsubConnectorProxy` acts is a python asyncio based proxy for `ZMQChannel` messages."""
 
-    @inject
-    def __init__(
-        self, *args: _t.Any, zmq_proxy: ZMQProxy = Provide[DI.zmq_proxy], **kwargs: _t.Any
-    ) -> None:
+    def __init__(self, *args: _t.Any, **kwargs: _t.Any) -> None:
         super().__init__(*args, **kwargs)
         self._topic = str(self.spec.source)
-        self._zmq_proxy = zmq_proxy
+        self._zmq_proxy: _t.Optional[ZMQProxy] = None
 
         self._send_channel: _t.Optional[ZMQChannel] = None
         self._recv_channel: _t.Optional[ZMQChannel] = None
 
+    @inject
+    async def _resolve_proxy(self, zmq_proxy: ZMQProxy = Provide[DI.zmq_proxy]) -> ZMQProxy:
+        return zmq_proxy
+
+    async def init(self) -> None:
+        """Resolve the shared proxy when execution starts."""
+        async with self._init_lock:
+            if self._zmq_proxy is None:
+                self._zmq_proxy = await self._resolve_proxy()
+
     def __getstate__(self) -> dict:
         state = self.__dict__.copy()
         for attr in ("_send_channel", "_recv_channel"):
@@ -311,8 +367,11 @@ def __setstate__(self, state: dict) -> None:
 
     async def connect_send(self) -> ZMQChannel:
         """Returns a `ZMQChannel` for sending pubsub messages."""
+        await self.init()
         if self._send_channel is not None:
             return self._send_channel
+        if self._zmq_proxy is None:
+            raise ChannelSetupError("ZMQ connector is not initialized")
         send_socket = create_socket(zmq.PUB, [(zmq.SNDHWM, self._maxsize)])
         send_socket.connect(self._zmq_proxy.xsub_addr)
         self._send_channel = ZMQChannel(
@@ -323,6 +382,9 @@ async def connect_send(self) -> ZMQChannel:
 
     async def connect_recv(self) -> ZMQChannel:
         """Returns a `ZMQChannel` for receiving pubsub messages."""
+        await self.init()
+        if self._zmq_proxy is None:
+            raise ChannelSetupError("ZMQ connector is not initialized")
         socket_opts: zmq_sockopts_t = [
             (zmq.RCVHWM, self._maxsize),
             (zmq.SUBSCRIBE, self._topic.encode("utf8")),
@@ -347,8 +409,11 @@ def __init__(self, *args: _t.Any, **kwargs: _t.Any) -> None:
 
     async def connect_recv(self) -> ZMQChannel:
         """Returns a `ZMQChannel` for receiving messages."""
+        await self.init()
         if self._recv_channel is not None:
             return self._recv_channel
+        if self._zmq_proxy is None:
+            raise ChannelSetupError("ZMQ connector is not initialized")
         self._push_address = await self._zmq_proxy.add_push_socket(
             self._topic, maxsize=self._maxsize
         )
@@ -384,6 +449,10 @@ def __init__(
                 raise ValueError(f"Unsupported connector mode: {self.spec.mode}")
         self._zmq_conn_impl: _ZMQConnector = zmq_conn_cls(*args, **kwargs)
 
+    async def init(self) -> None:
+        """Allocate resources for the selected ZMQ implementation."""
+        await self._zmq_conn_impl.init()
+
     @property
     def zmq_address(self) -> str:
         """The ZMQ address used for communication."""

plugboard/library/file_io.py

@@ -1,5 +1,6 @@
 """Provides `FileReader` and `FileWriter` components to access files from Plugboard models."""
 
+import asyncio
 from collections import deque
 from pathlib import Path
 import typing as _t
@@ -106,7 +107,12 @@ def __init__(
             raise ValueError("Only CSV files support chunked writing.")
         self._storage_options = storage_options or {}
         self._header_written = False
-        self._check_file()
+
+    async def init(self) -> None:
+        """Open and truncate the destination when execution starts."""
+        await asyncio.to_thread(self._check_file)
+        self._header_written = False
+        await super().init()
 
     def _check_file(self) -> None:
         with fsspec.open(self._file_path, mode="w", **self._storage_options):

plugboard/process/local_process.py

@@ -57,6 +57,10 @@ async def _connect_state(self) -> None:
 
     async def init(self) -> None:
         """Performs component initialisation actions."""
+        self.validate()
+        async with asyncio.TaskGroup() as tg:
+            for connector in self.connectors.values():
+                tg.create_task(connector.init())
         async with asyncio.TaskGroup() as tg:
             await self.connect_state()
             await self._connect_components()

plugboard/process/process.py

@@ -109,12 +109,21 @@ async def _set_status(self, status: Status, publish: bool = True) -> None:
     @abstractmethod
     async def init(self) -> None:
         """Performs component initialisation actions."""
+        self.validate()
+        self._is_initialised = True
+        await self._set_status(Status.INIT)
+
+    def validate(self) -> None:
+        """Validate the process topology without acquiring external resources."""
+        for component in self.components.values():
+            if not hasattr(component, "_state_is_connected"):
+                raise ValidationError(
+                    "Component invalid: did you forget to call super().__init__ in the constructor?"
+                )
         errors = validate_process(self.dict())
         if errors:
             msg = "Process validation failed:\n" + "\n".join(errors)
             raise ValidationError(msg)
-        self._is_initialised = True
-        await self._set_status(Status.INIT)
 
     @abstractmethod
     async def step(self) -> None: