fix: allow calling Actor.reboot() from migrating handler, align reb…

…oot behavior with JS SDK (#361)

This fixes several issues with the `Actor.reboot()` behavior:
- `Actor.reboot()` waits for all event handlers to finish, but if itself
it was called in an event handler, it would be waiting for itself,
getting into a deadlock
- `Actor.reboot()` in the JS SDK triggers event handlers for the
`migrating` and `persistState` events, but in the Python SDK it was
triggering only the `persistState` handlers

This aligns the behavior to work like the JS SDK, and prevents reboot
getting into an infinite loop by allowing it to be called only once.

Related PR in JS SDK: apify/apify-sdk-js#345

docs/03-concepts/04-actor-events.mdx

@@ -40,6 +40,8 @@ During its runtime, the Actor receives Actor events sent by the Apify platform o
                 {' '}to another worker server soon.</p>
                 You can use it to persist the state of the Actor so that once it is executed again on the new server,
                 it doesn't have to start over from the beginning.
+                Once you have persisted the state of your Actor, you can call <a href="../../reference/class/Actor#reboot"><code>Actor.reboot()</code></a>
+                to reboot the Actor and trigger the migration immediately, to speed up the process.
             </td>
         </tr>
         <tr>

pyproject.toml

@@ -51,6 +51,7 @@ cryptography = ">=42.0.0"
 # https://github.com/apify/apify-sdk-python/issues/348
 httpx = "~0.27.0"
 lazy-object-proxy = ">=1.10.0"
+more_itertools = ">=10.2.0"
 scrapy = { version = ">=2.11.0", optional = true }
 typing-extensions = ">=4.1.0"
 websockets = ">=10.0 <14.0.0"

src/apify/_actor.py

@@ -7,13 +7,14 @@
 from typing import TYPE_CHECKING, Any, Callable, TypeVar, cast
 
 from lazy_object_proxy import Proxy
+from more_itertools import flatten
 from pydantic import AliasChoices
 
 from apify_client import ApifyClientAsync
 from apify_shared.consts import ActorEnvVars, ActorExitCodes, ApifyEnvVars
 from apify_shared.utils import ignore_docs, maybe_extract_enum_member_value
 from crawlee import service_container
-from crawlee.events._types import Event, EventPersistStateData
+from crawlee.events._types import Event, EventMigratingData, EventPersistStateData
 
 from apify._configuration import Configuration
 from apify._consts import EVENT_LISTENERS_TIMEOUT
@@ -48,6 +49,7 @@ class _ActorType:
     _apify_client: ApifyClientAsync
     _configuration: Configuration
     _is_exiting = False
+    _is_rebooting = False
 
     def __init__(
         self,
@@ -839,12 +841,32 @@ async def reboot(
             self.log.error('Actor.reboot() is only supported when running on the Apify platform.')
             return
 
+        if self._is_rebooting:
+            self.log.debug('Actor is already rebooting, skipping the additional reboot call.')
+            return
+
+        self._is_rebooting = True
+
         if not custom_after_sleep:
             custom_after_sleep = self._configuration.metamorph_after_sleep
 
-        self._event_manager.emit(event=Event.PERSIST_STATE, event_data=EventPersistStateData(is_migrating=True))
+        # Call all the listeners for the PERSIST_STATE and MIGRATING events, and wait for them to finish.
+        # PERSIST_STATE listeners are called to allow the Actor to persist its state before the reboot.
+        # MIGRATING listeners are called to allow the Actor to gracefully stop in-progress tasks before the reboot.
+        # Typically, crawlers are listening for the MIIGRATING event to stop processing new requests.
+        # We can't just emit the events and wait for all listeners to finish,
+        # because this method might be called from an event listener itself, and we would deadlock.
+        persist_state_listeners = flatten(
+            (self._event_manager._listeners_to_wrappers[Event.PERSIST_STATE] or {}).values()  # noqa: SLF001
+        )
+        migrating_listeners = flatten(
+            (self._event_manager._listeners_to_wrappers[Event.MIGRATING] or {}).values()  # noqa: SLF001
+        )
 
-        await self._event_manager.__aexit__(None, None, None)
+        await asyncio.gather(
+            *[listener(EventPersistStateData(is_migrating=True)) for listener in persist_state_listeners],
+            *[listener(EventMigratingData()) for listener in migrating_listeners],
+        )
 
         if not self._configuration.actor_run_id:
             raise RuntimeError('actor_run_id cannot be None when running on the Apify platform.')