[3.12] gh-108388: Convert test_concurrent_futures to package (#108401) (#108443)

gh-108388: Convert test_concurrent_futures to package (#108401)

Convert test_concurrent_futures to a package of sub-tests.

(cherry picked from commit aa6f787faa)

Lib/test/test_concurrent_futures/test_thread_pool.py

@@ -0,0 +1,98 @@
+import contextlib
+import multiprocessing as mp
+import multiprocessing.process
+import multiprocessing.util
+import os
+import threading
+import unittest
+from concurrent import futures
+
+from .executor import ExecutorTest, mul
+from .util import BaseTestCase, ThreadPoolMixin, setup_module
+
+
+class ThreadPoolExecutorTest(ThreadPoolMixin, ExecutorTest, BaseTestCase):
+    def test_map_submits_without_iteration(self):
+        """Tests verifying issue 11777."""
+        finished = []
+        def record_finished(n):
+            finished.append(n)
+
+        self.executor.map(record_finished, range(10))
+        self.executor.shutdown(wait=True)
+        self.assertCountEqual(finished, range(10))
+
+    def test_default_workers(self):
+        executor = self.executor_type()
+        expected = min(32, (os.cpu_count() or 1) + 4)
+        self.assertEqual(executor._max_workers, expected)
+
+    def test_saturation(self):
+        executor = self.executor_type(4)
+        def acquire_lock(lock):
+            lock.acquire()
+
+        sem = threading.Semaphore(0)
+        for i in range(15 * executor._max_workers):
+            executor.submit(acquire_lock, sem)
+        self.assertEqual(len(executor._threads), executor._max_workers)
+        for i in range(15 * executor._max_workers):
+            sem.release()
+        executor.shutdown(wait=True)
+
+    def test_idle_thread_reuse(self):
+        executor = self.executor_type()
+        executor.submit(mul, 21, 2).result()
+        executor.submit(mul, 6, 7).result()
+        executor.submit(mul, 3, 14).result()
+        self.assertEqual(len(executor._threads), 1)
+        executor.shutdown(wait=True)
+
+    @unittest.skipUnless(hasattr(os, 'register_at_fork'), 'need os.register_at_fork')
+    def test_hang_global_shutdown_lock(self):
+        # bpo-45021: _global_shutdown_lock should be reinitialized in the child
+        # process, otherwise it will never exit
+        def submit(pool):
+            pool.submit(submit, pool)
+
+        with futures.ThreadPoolExecutor(1) as pool:
+            pool.submit(submit, pool)
+
+            for _ in range(50):
+                with futures.ProcessPoolExecutor(1, mp_context=mp.get_context('fork')) as workers:
+                    workers.submit(tuple)
+
+    def test_executor_map_current_future_cancel(self):
+        stop_event = threading.Event()
+        log = []
+
+        def log_n_wait(ident):
+            log.append(f"{ident=} started")
+            try:
+                stop_event.wait()
+            finally:
+                log.append(f"{ident=} stopped")
+
+        with self.executor_type(max_workers=1) as pool:
+            # submit work to saturate the pool
+            fut = pool.submit(log_n_wait, ident="first")
+            try:
+                with contextlib.closing(
+                    pool.map(log_n_wait, ["second", "third"], timeout=0)
+                ) as gen:
+                    with self.assertRaises(TimeoutError):
+                        next(gen)
+            finally:
+                stop_event.set()
+            fut.result()
+        # ident='second' is cancelled as a result of raising a TimeoutError
+        # ident='third' is cancelled because it remained in the collection of futures
+        self.assertListEqual(log, ["ident='first' started", "ident='first' stopped"])
+
+
+def setUpModule():
+    setup_module()
+
+
+if __name__ == "__main__":
+    unittest.main()