Add timeout to test_dask_use_explicit_comms

Add timeout to `test_dask_use_explicit_comms` with SIGINT (i.e.,
KeyboardInterrupt) hoping that we can get a stacktrace that can help
identifying the cause of the test deadlock in CI.

dask_cuda/tests/test_explicit_comms.py

@@ -1,6 +1,9 @@
 import asyncio
 import multiprocessing as mp
 import os
+import signal
+import time
+from functools import partial
 from unittest.mock import patch
 
 import numpy as np
@@ -175,7 +178,7 @@ def test_dataframe_shuffle(backend, protocol, nworkers, _partitions):
 
 
 @pytest.mark.parametrize("in_cluster", [True, False])
-def test_dask_use_explicit_comms(in_cluster):
+def _test_dask_use_explicit_comms(in_cluster):
     def check_shuffle():
         """Check if shuffle use explicit-comms by search for keys named
         'explicit-comms-shuffle'
@@ -217,6 +220,31 @@ def check_shuffle():
         check_shuffle()
 
 
+@pytest.mark.parametrize("in_cluster", [True, False])
+def test_dask_use_explicit_comms(in_cluster):
+    def _timeout(process, function, timeout):
+        if process.is_alive():
+            function()
+        timeout = time.time() + timeout
+        while process.is_alive() and time.time() < timeout:
+            time.sleep(0.1)
+
+    p = mp.Process(target=_test_dask_use_explicit_comms, args=(in_cluster,))
+    p.start()
+
+    # Timeout before killing process
+    _timeout(p, lambda: None, 60.0)
+
+    # Send SIGINT (i.e., KeyboardInterrupt) hoping we get a stack trace.
+    _timeout(p, partial(p._popen._send_signal, signal.SIGINT), 3.0)
+
+    # SIGINT didn't work, kill process.
+    _timeout(p, p.kill, 3.0)
+
+    assert not p.is_alive()
+    assert p.exitcode == 0
+
+
 def _test_dataframe_shuffle_merge(backend, protocol, n_workers):
     if backend == "cudf":
         cudf = pytest.importorskip("cudf")