Iterate subprocesses in-place (#2373)

* replace suprocesses inplace

* list is not resized, no need for copying

uvicorn/supervisors/multiprocess.py

@@ -134,7 +134,7 @@ def join_all(self) -> None:
             process.join()
 
     def restart_all(self) -> None:
-        for idx, process in enumerate(tuple(self.processes)):
+        for idx, process in enumerate(self.processes):
             process.terminate()
             process.join()
             new_process = Process(self.config, self.target, self.sockets)
@@ -163,7 +163,7 @@ def keep_subprocess_alive(self) -> None:
         if self.should_exit.is_set():
             return  # parent process is exiting, no need to keep subprocess alive
 
-        for idx, process in enumerate(tuple(self.processes)):
+        for idx, process in enumerate(self.processes):
             if process.is_alive():
                 continue
 
@@ -174,10 +174,9 @@ def keep_subprocess_alive(self) -> None:
                 return
 
             logger.info(f"Child process [{process.pid}] died")
-            del self.processes[idx]
             process = Process(self.config, self.target, self.sockets)
             process.start()
-            self.processes.append(process)
+            self.processes[idx] = process
 
     def handle_signals(self) -> None:
         for sig in tuple(self.signal_queue):