WebHost: fix gen timeout/exception resource handling (#5540)

* WebHost: reset Generator proc title on error

* WebHost: fix shutting down autogen

This is still not perfect but solves some of the issues.

* WebHost: properly propagate JOB_TIME

* WebHost: handle autogen shutdown

Utils.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import asyncio
+import concurrent.futures
 import json
 import typing
 import builtins
@@ -1138,3 +1139,40 @@ def is_iterable_except_str(obj: object) -> TypeGuard[typing.Iterable[typing.Any]
     if isinstance(obj, str):
         return False
     return isinstance(obj, typing.Iterable)
+
+
+class DaemonThreadPoolExecutor(concurrent.futures.ThreadPoolExecutor):
+    """
+    ThreadPoolExecutor that uses daemonic threads that do not keep the program alive.
+    NOTE: use this with caution because killed threads will not properly clean up.
+    """
+
+    def _adjust_thread_count(self):
+        # see upstream ThreadPoolExecutor for details
+        import threading
+        import weakref
+        from concurrent.futures.thread import _worker
+
+        if self._idle_semaphore.acquire(timeout=0):
+            return
+
+        def weakref_cb(_, q=self._work_queue):
+            q.put(None)
+
+        num_threads = len(self._threads)
+        if num_threads < self._max_workers:
+            thread_name = f"{self._thread_name_prefix or self}_{num_threads}"
+            t = threading.Thread(
+                name=thread_name,
+                target=_worker,
+                args=(
+                    weakref.ref(self, weakref_cb),
+                    self._work_queue,
+                    self._initializer,
+                    self._initargs,
+                ),
+                daemon=True,
+            )
+            t.start()
+            self._threads.add(t)
+            # NOTE: don't add to _threads_queues so we don't block on shutdown