pythongh-113205: test_multiprocessing.test_terminate: Test the API on threadpools (python#114186)

pythongh-113205: test_multiprocessing.test_terminate: Test the API works on threadpools

Threads can't be forced to terminate (without potentially corrupting too much
state), so the  expected behaviour of `ThreadPool.terminate` is to wait for
the currently executing tasks to finish.

The entire test was skipped in pythonGH-110848 (0e9c364).
Instead of skipping it entirely, we should ensure the API eventually succeeds:
use a shorter timeout.

For the record: on my machine, when the test is un-skipped, the task manages to
start in about 1.5% cases.

Author: encukou

Lib/test/_test_multiprocessing.py

@@ -2693,12 +2693,17 @@ def test_make_pool(self):
                 p.join()
 
     def test_terminate(self):
+        # Simulate slow tasks which take "forever" to complete
+        sleep_time = support.LONG_TIMEOUT
+
         if self.TYPE == 'threads':
-            self.skipTest("Threads cannot be terminated")
+            # Thread pool workers can't be forced to quit, so if the first
+            # task starts early enough, we will end up waiting for it.
+            # Sleep for a shorter time, so the test doesn't block.
+            sleep_time = 1
 
-        # Simulate slow tasks which take "forever" to complete
         p = self.Pool(3)
-        args = [support.LONG_TIMEOUT for i in range(10_000)]
+        args = [sleep_time for i in range(10_000)]
         result = p.map_async(time.sleep, args, chunksize=1)
         p.terminate()
         p.join()