async fixes in kernel usage handler

- handle get_msg being async _or not_
- use async poller to avoid blocking while waiting for usage response

Author: minrk

jupyter_resource_usage/api.py

@@ -1,21 +1,15 @@
 import json
 from concurrent.futures import ThreadPoolExecutor
+from inspect import isawaitable
 
 import psutil
-import zmq
+import zmq.asyncio
 from jupyter_client.jsonutil import date_default
 from jupyter_server.base.handlers import APIHandler
-from jupyter_server.utils import url_path_join
 from packaging import version
 from tornado import web
 from tornado.concurrent import run_on_executor
 
-try:
-    # Traitlets >= 4.3.3
-    from traitlets import Callable
-except ImportError:
-    from .utils import Callable
-
 
 try:
     import ipykernel
@@ -24,8 +18,6 @@
 except ImportError:
     USAGE_IS_SUPPORTED = False
 
-MAX_RETRIES = 3
-
 
 class ApiHandler(APIHandler):
     executor = ThreadPoolExecutor(max_workers=5)
@@ -113,17 +105,18 @@ async def get(self, matched_part=None, *args, **kwargs):
         usage_request = session.msg("usage_request", {})
 
         control_channel.send(usage_request)
-        poller = zmq.Poller()
+        poller = zmq.asyncio.Poller()
         control_socket = control_channel.socket
         poller.register(control_socket, zmq.POLLIN)
-        for i in range(1, MAX_RETRIES + 1):
-            timeout_ms = 1000 * i
-            events = dict(poller.poll(timeout_ms))
-            if not events:
-                self.write(json.dumps({}))
-                break
-            if control_socket not in events:
-                continue
-            res = await client.control_channel.get_msg(timeout=0)
+        # previous behavior was 3 retries: 1 + 2 + 3 = 6 seconds
+        timeout_ms = 6_000
+        events = dict(await poller.poll(timeout_ms))
+        if control_socket not in events:
+            self.write(json.dumps({}))
+        else:
+            res = client.control_channel.get_msg(timeout=0)
+            if isawaitable(res):
+                # control_channel.get_msg may return a Future,
+                # depending on configured KernelManager class
+                res = await res
             self.write(json.dumps(res, default=date_default))
-            break

pyproject.toml

@@ -39,6 +39,7 @@ dependencies = [
     "jupyter_server>=1.0",
     "prometheus_client",
     "psutil~=5.6",
+    "pyzmq>=19",
 ]
 dynamic = ["version"]