From 2737f07b6bcb3ca19b8582b5319341c01fd0e015 Mon Sep 17 00:00:00 2001
From: Helmut Grohne <helmut@subdivi.de>
Date: Wed, 21 Feb 2024 14:25:45 +0100
Subject: examples/cgroup.py: drive ravel using asyncio

---
 examples/cgroup.py | 44 +++++++++++++++++++++++++-------------------
 1 file changed, 25 insertions(+), 19 deletions(-)

diff --git a/examples/cgroup.py b/examples/cgroup.py
index baacf35..9a01d0d 100755
--- a/examples/cgroup.py
+++ b/examples/cgroup.py
@@ -6,10 +6,10 @@
 (inside the namespace) becomes writeable to the user.
 """
 
+import asyncio
 import os
 import pathlib
 import sys
-import time
 
 try:
     import ravel
@@ -33,46 +33,50 @@ def get_cgroup(pid: int = -1) -> pathlib.PurePath:
     )
 
 
-def start_transient_unit_with_ravel(pid: int) -> None:
+async def start_transient_unit_with_ravel(pid: int) -> None:
     """Call the StartTransientUnit dbus method on the user manager for the
     given pid.
     """
-    bus = ravel.session_bus()
+    bus = await ravel.session_bus_async()
     jobs_removed = {}
+    scope_job = None
     systemd_path = "/org/freedesktop/systemd1"
     systemd_iface = "org.freedesktop.systemd1.Manager"
+    scope_created = asyncio.get_running_loop().create_future()
 
     @ravel.signal(name="JobRemoved", in_signature="uoss")
     def handle_job_removed(_1, path, _2, result):
         nonlocal jobs_removed
-        jobs_removed[path] = result
+        nonlocal scope_job
+        nonlocal scope_created
+        if scope_job is None:
+            jobs_removed[path] = result
+        elif path == scope_job:
+            scope_created.set_result(result)
 
     bus.listen_signal(
         systemd_path, False, systemd_iface, "JobRemoved", handle_job_removed
     )
-    unitpath = (
+    scope_job = (
         bus["org.freedesktop.systemd1"][systemd_path]
         .get_interface(systemd_iface)
         .StartTransientUnit(
             f"cgroup-{pid}.scope", "fail", [("PIDs", ("au", [pid]))], []
         )
     )[0]
-    now = time.monotonic()
-    deadline = now + 60
-    while unitpath not in jobs_removed:
-        if not bus.connection.read_write_dispatch(timeout=deadline - now):
-            break
-        now = time.monotonic()
-        if now > deadline:
-            break
+    if scope_job in jobs_removed:
+        scope_created.set_result(jobs_removed[scope_job])
+    else:
+        try:
+            await asyncio.wait_for(scope_created, 60)
+        except TimeoutError:
+            print("Error: timed out waiting for StartTransientUnit")
+            sys.exit(1)
     bus.unlisten_signal(
         systemd_path, False, systemd_iface, "JobRemoved", handle_job_removed
     )
-    if unitpath not in jobs_removed:
-        print("Error: timed out waiting for StartTransientUnit")
-        sys.exit(1)
-    if jobs_removed[unitpath] != "done":
-        print("Error: StartTransientUnit failed: " + jobs_removed[unitpath])
+    if scope_created.result() != "done":
+        print("Error: StartTransientUnit failed: " + scope_created.result())
         sys.exit(1)
 
 
@@ -86,7 +90,9 @@ def main() -> None:
         # hiearchy is immediatly writeable. For others, we may create a scope
         # unit.
         if ravel is not None:
-            start_transient_unit_with_ravel(os.getpid())
+            asyncio.get_event_loop().run_until_complete(
+                start_transient_unit_with_ravel(os.getpid())
+            )
             mycgroup = get_cgroup()
         else:
             # Re-execute ourselves via systemd-run.
-- 
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