Plugins: replace running bool with PluginStatus enum

This enables the plugin to read the status of the
four formal states a plugin can be in. Previously
even though the four states existed implicitly,
it could only be differentiated between the
STARTED/STOPPED state based on the `running`
bool.

This change also has the nice benefit that we
can make stronger assumptions about the status
inside `start()` and raise an exception if
`start()` was called on a plugin that isn't in
the correct status to call `start()`

trinity/extensibility/exceptions.py

@@ -6,7 +6,15 @@
 class EventBusNotReady(BaseTrinityError):
     """
     Raised when a plugin tried to access an :class:`~lahja.eventbus.EventBus` before the plugin
-    had received its :meth:`~trinity.extensibility.plugin.BasePlugin.ready` call.
+    had received its :meth:`~trinity.extensibility.plugin.BasePlugin.on_ready` call.
+    """
+    pass
+
+
+class InvalidPluginStatus(BaseTrinityError):
+    """
+    Raised when it was attempted to perform an action while the current
+    :class:`~trinity.extensibility.plugin.PluginStatus` does not allow to perform such action.
     """
     pass
 

trinity/extensibility/plugin.py

@@ -8,6 +8,10 @@
     _SubParsersAction,
 )
 import asyncio
+from enum import (
+    auto,
+    Enum,
+)
 import logging
 from multiprocessing import (
     Process
@@ -38,6 +42,7 @@
 )
 from trinity.extensibility.exceptions import (
     EventBusNotReady,
+    InvalidPluginStatus,
 )
 from trinity.utils.ipc import (
     kill_process_gracefully
@@ -50,6 +55,16 @@
 )
 
 
+class PluginStatus(Enum):
+    NOT_READY = auto()
+    READY = auto()
+    STARTED = auto()
+    STOPPED = auto()
+
+
+INVALID_START_STATUS = (PluginStatus.NOT_READY, PluginStatus.STARTED,)
+
+
 class TrinityBootInfo(NamedTuple):
     args: Namespace
     trinity_config: TrinityConfig
@@ -65,7 +80,7 @@ class PluginContext:
 
     The :class:`~trinity.extensibility.plugin.PluginContext` is set during startup and is
     guaranteed to exist by the time that a plugin receives its
-    :meth:`~trinity.extensibility.plugin.BasePlugin.ready` call.
+    :meth:`~trinity.extensibility.plugin.BasePlugin.on_ready` call.
     """
 
     def __init__(self, endpoint: Endpoint, boot_info: TrinityBootInfo) -> None:
@@ -112,7 +127,7 @@ def trinity_config(self) -> TrinityConfig:
 class BasePlugin(ABC):
 
     context: PluginContext = None
-    running: bool = False
+    status: PluginStatus = PluginStatus.NOT_READY
 
     @property
     @abstractmethod
@@ -140,13 +155,28 @@ def event_bus(self) -> Endpoint:
 
         return self.context.event_bus
 
+    @property
+    def running(self) -> bool:
+        """
+        Return ``True`` if the ``status`` is ``PluginStatus.STARTED``, otherwise return ``False``.
+        """
+        return self.status is PluginStatus.STARTED
+
     def set_context(self, context: PluginContext) -> None:
         """
         Set the :class:`~trinity.extensibility.plugin.PluginContext` for this plugin.
         """
         self.context = context
 
     def ready(self) -> None:
+        """
+        Set the ``status`` to ``PluginStatus.READY`` and delegate to
+        :meth:`~trinity.extensibility.plugin.BasePlugin.on_ready`
+        """
+        self.status = PluginStatus.READY
+        self.on_ready()
+
+    def on_ready(self) -> None:
         """
         Notify the plugin that it is ready to bootstrap itself. Plugins can rely
         on the :class:`~trinity.extensibility.plugin.PluginContext` to be set
@@ -157,7 +187,7 @@ def ready(self) -> None:
     def configure_parser(self, arg_parser: ArgumentParser, subparser: _SubParsersAction) -> None:
         """
         Give the plugin a chance to amend the Trinity CLI argument parser. This hook is called
-        before :meth:`~trinity.extensibility.plugin.BasePlugin.ready`
+        before :meth:`~trinity.extensibility.plugin.BasePlugin.on_ready`
         """
         pass
 
@@ -167,7 +197,13 @@ def start(self) -> None:
         to ``True``. Broadcast a :class:`~trinity.extensibility.events.PluginStartedEvent` on the
         :class:`~lahja.eventbus.EventBus` and hence allow other plugins to act accordingly.
         """
-        self.running = True
+
+        if self.status in INVALID_START_STATUS:
+            raise InvalidPluginStatus(
+                f"Can not start plugin when the plugin status is {self.status}"
+            )
+
+        self.status = PluginStatus.STARTED
         self.do_start()
         self.event_bus.broadcast(
             PluginStartedEvent(type(self))
@@ -202,7 +238,7 @@ def stop(self) -> None:
         plugin to stop and setting ``running`` to ``False``.
         """
         self.do_stop()
-        self.running = False
+        self.status = PluginStatus.STOPPED
 
 
 class BaseAsyncStopPlugin(BasePlugin):
@@ -223,7 +259,7 @@ async def stop(self) -> None:
         plugin to stop asynchronously and setting ``running`` to ``False``.
         """
         await self.do_stop()
-        self.running = False
+        self.status = PluginStatus.STOPPED
 
 
 class BaseMainProcessPlugin(BasePlugin):
@@ -252,7 +288,7 @@ def start(self) -> None:
         """
         Prepare the plugin to get started and eventually call ``do_start`` in a separate process.
         """
-        self.running = True
+        self.status = PluginStatus.STARTED
         self._process = ctx.Process(
             target=self._prepare_start,
         )

trinity/plugins/builtin/ethstats/plugin.py

@@ -71,7 +71,7 @@ def configure_parser(self, arg_parser: ArgumentParser, subparser: _SubParsersAct
             default=os.environ.get('ETHSTATS_NODE_CONTACT', ''),
         )
 
-    def ready(self) -> None:
+    def on_ready(self) -> None:
         args = self.context.args
 
         if not args.ethstats:

trinity/plugins/builtin/json_rpc/plugin.py

@@ -33,7 +33,7 @@ class JsonRpcServerPlugin(BaseIsolatedPlugin):
     def name(self) -> str:
         return "JSON-RPC Server"
 
-    def ready(self) -> None:
+    def on_ready(self) -> None:
         if not self.context.args.disable_rpc:
             self.start()
 

trinity/plugins/builtin/light_peer_chain_bridge/plugin.py

@@ -40,7 +40,7 @@ class LightPeerChainBridgePlugin(BaseAsyncStopPlugin):
     def name(self) -> str:
         return "LightPeerChain Bridge"
 
-    def ready(self) -> None:
+    def on_ready(self) -> None:
         if self.context.trinity_config.sync_mode != SYNC_LIGHT:
             return
 

trinity/plugins/builtin/tx_pool/plugin.py

@@ -54,7 +54,7 @@ def configure_parser(self, arg_parser: ArgumentParser, subparser: _SubParsersAct
             help="Enables the Transaction Pool (experimental)",
         )
 
-    def ready(self) -> None:
+    def on_ready(self) -> None:
 
         light_mode = self.context.args.sync_mode == SYNC_LIGHT
         self.is_enabled = self.context.args.tx_pool and not light_mode