feat(framework) Introduce RunTracker (#3561)

Co-authored-by: Charles Beauville <charels@flower.ai>

src/py/flwr/client/app.py

@@ -14,8 +14,10 @@
 # ==============================================================================
 """Flower client app."""
 
+import signal
 import sys
 import time
+from dataclasses import dataclass
 from logging import DEBUG, ERROR, INFO, WARN
 from typing import Callable, ContextManager, Optional, Tuple, Type, Union
 
@@ -37,7 +39,7 @@
 )
 from flwr.common.logger import log, warn_deprecated_feature
 from flwr.common.message import Error
-from flwr.common.retry_invoker import RetryInvoker, exponential
+from flwr.common.retry_invoker import RetryInvoker, RetryState, exponential
 
 from .grpc_client.connection import grpc_connection
 from .grpc_rere_client.connection import grpc_request_response
@@ -263,6 +265,29 @@ def _load_client_app() -> ClientApp:
         transport, server_address
     )
 
+    run_tracker = _RunTracker()
+
+    def _on_sucess(retry_state: RetryState) -> None:
+        if retry_state.tries > 1:
+            log(
+                INFO,
+                "Connection successful after %.2f seconds and %s tries.",
+                retry_state.elapsed_time,
+                retry_state.tries,
+            )
+            if run_tracker.create_node:
+                run_tracker.create_node()
+
+    def _on_backoff(retry_state: RetryState) -> None:
+        if retry_state.tries == 1:
+            log(WARN, "Connection attempt failed, retrying...")
+        else:
+            log(
+                DEBUG,
+                "Connection attempt failed, retrying in %.2f seconds",
+                retry_state.actual_wait,
+            )
+
     retry_invoker = RetryInvoker(
         wait_gen_factory=exponential,
         recoverable_exceptions=connection_error_type,
@@ -278,25 +303,8 @@ def _load_client_app() -> ClientApp:
             if retry_state.tries > 1
             else None
         ),
-        on_success=lambda retry_state: (
-            log(
-                INFO,
-                "Connection successful after %.2f seconds and %s tries.",
-                retry_state.elapsed_time,
-                retry_state.tries,
-            )
-            if retry_state.tries > 1
-            else None
-        ),
-        on_backoff=lambda retry_state: (
-            log(WARN, "Connection attempt failed, retrying...")
-            if retry_state.tries == 1
-            else log(
-                DEBUG,
-                "Connection attempt failed, retrying in %.2f seconds",
-                retry_state.actual_wait,
-            )
-        ),
+        on_success=_on_sucess,
+        on_backoff=_on_backoff,
     )
 
     node_state = NodeState()
@@ -579,3 +587,20 @@ def _init_connection(transport: Optional[str], server_address: str) -> Tuple[
         )
 
     return connection, address, error_type
+
+
+@dataclass
+class _RunTracker:
+    create_node: Optional[Callable[[], None]] = None
+    interrupt: bool = False
+
+    def register_signal_handler(self) -> None:
+        """Register handlers for exit signals."""
+
+        def signal_handler(sig, frame):  # type: ignore
+            # pylint: disable=unused-argument
+            self.interrupt = True
+            raise StopIteration from None
+
+        signal.signal(signal.SIGINT, signal_handler)
+        signal.signal(signal.SIGTERM, signal_handler)