Improve shutdown robustness when using --reload or multiprocessing

uvicorn/subprocess.py

@@ -4,6 +4,7 @@
 """
 import multiprocessing
 import os
+import signal
 import sys
 
 multiprocessing.allow_connection_pickling()
@@ -59,3 +60,13 @@ def subprocess_started(config, target, sockets, stdin_fileno):
 
     # Now we can call into `Server.run(sockets=sockets)`
     target(sockets=sockets)
+
+
+def shutdown_subprocess(pid):
+    """
+    Helper to attempt cleanly shutting down a subprocess. May fail with an exception.
+
+    * pid - Process identifier.
+    """
+    os.kill(pid, signal.SIGINT)
+    os.waitpid(pid, 0)

uvicorn/supervisors/basereload.py

@@ -5,7 +5,7 @@
 
 import click
 
-from uvicorn.subprocess import get_subprocess
+from uvicorn.subprocess import get_subprocess, shutdown_subprocess
 
 HANDLED_SIGNALS = (
     signal.SIGINT,  # Unix signal 2. Sent by Ctrl+C.
@@ -22,11 +22,18 @@ def __init__(self, config, target, sockets):
         self.sockets = sockets
         self.should_exit = threading.Event()
         self.pid = os.getpid()
+        self.process = None
 
     def signal_handler(self, sig, frame):
         """
         A signal handler that is registered with the parent process.
         """
+        if self.process is not None:
+            try:
+                shutdown_subprocess(self.process.pid)
+            except Exception as exc:
+                logger.error(f"Could not stop child process {self.process.pid}: {exc}")
+
         self.should_exit.set()
 
     def run(self):
@@ -36,6 +43,7 @@ def run(self):
                 self.restart()
         self.shutdown()
 
+
     def startup(self):
         message = "Started reloader process [{}]".format(str(self.pid))
         color_message = "Started reloader process [{}]".format(

uvicorn/supervisors/multiprocess.py

@@ -5,7 +5,7 @@
 
 import click
 
-from uvicorn.subprocess import get_subprocess
+from uvicorn.subprocess import get_subprocess, shutdown_subprocess
 
 HANDLED_SIGNALS = (
     signal.SIGINT,  # Unix signal 2. Sent by Ctrl+C.
@@ -28,6 +28,13 @@ def signal_handler(self, sig, frame):
         """
         A signal handler that is registered with the parent process.
         """
+
+        for process in self.processes:
+            try:
+                shutdown_subprocess(process.pid)
+            except Exception as exc:
+                logger.error(f"Could not stop child process {process.pid}: {exc}")
+
         self.should_exit.set()
 
     def run(self):

uvicorn/supervisors/watchdogreload.py

@@ -1,10 +1,11 @@
 import logging
 from os import path
 
-from uvicorn.supervisors.basereload import BaseReload
 from watchdog.events import PatternMatchingEventHandler
 from watchdog.observers import Observer
 
+from uvicorn.supervisors.basereload import BaseReload
+
 logger = logging.getLogger("uvicorn.error")