bpo-31234: Add test.support.wait_threads_exit() (#3578)

Use _thread.count() to wait until threads exit. The new context
manager prevents the "dangling thread" warning.

Lib/test/test_threadsignals.py

@@ -4,8 +4,8 @@ import unittest
 import signal
 import os
 import sys
-from test.support import run_unittest, import_module
-thread = import_module('_thread')
+from test import support
+thread = support.import_module('_thread')
 import time
 
 if (sys.platform[:3] == 'win'):
@@ -39,13 +39,15 @@ def send_signals():
 class ThreadSignals(unittest.TestCase):
 
     def test_signals(self):
-        # Test signal handling semantics of threads.
-        # We spawn a thread, have the thread send two signals, and
-        # wait for it to finish. Check that we got both signals
-        # and that they were run by the main thread.
-        signalled_all.acquire()
-        self.spawnSignallingThread()
-        signalled_all.acquire()
+        with support.wait_threads_exit():
+            # Test signal handling semantics of threads.
+            # We spawn a thread, have the thread send two signals, and
+            # wait for it to finish. Check that we got both signals
+            # and that they were run by the main thread.
+            signalled_all.acquire()
+            self.spawnSignallingThread()
+            signalled_all.acquire()
+
         # the signals that we asked the kernel to send
         # will come back, but we don't know when.
         # (it might even be after the thread exits
@@ -115,17 +117,19 @@ class ThreadSignals(unittest.TestCase):
             # thread.
             def other_thread():
                 rlock.acquire()
-            thread.start_new_thread(other_thread, ())
-            # Wait until we can't acquire it without blocking...
-            while rlock.acquire(blocking=False):
-                rlock.release()
-                time.sleep(0.01)
-            signal.alarm(1)
-            t1 = time.time()
-            self.assertRaises(KeyboardInterrupt, rlock.acquire, timeout=5)
-            dt = time.time() - t1
-            # See rationale above in test_lock_acquire_interruption
-            self.assertLess(dt, 3.0)
+
+            with support.wait_threads_exit():
+                thread.start_new_thread(other_thread, ())
+                # Wait until we can't acquire it without blocking...
+                while rlock.acquire(blocking=False):
+                    rlock.release()
+                    time.sleep(0.01)
+                signal.alarm(1)
+                t1 = time.time()
+                self.assertRaises(KeyboardInterrupt, rlock.acquire, timeout=5)
+                dt = time.time() - t1
+                # See rationale above in test_lock_acquire_interruption
+                self.assertLess(dt, 3.0)
         finally:
             signal.signal(signal.SIGALRM, oldalrm)
 
@@ -133,6 +137,7 @@ class ThreadSignals(unittest.TestCase):
         self.sig_recvd = False
         def my_handler(signal, frame):
             self.sig_recvd = True
+
         old_handler = signal.signal(signal.SIGUSR1, my_handler)
         try:
             def other_thread():
@@ -147,14 +152,16 @@ class ThreadSignals(unittest.TestCase):
                 # the lock acquisition.  Then we'll let it run.
                 time.sleep(0.5)
                 lock.release()
-            thread.start_new_thread(other_thread, ())
-            # Wait until we can't acquire it without blocking...
-            while lock.acquire(blocking=False):
-                lock.release()
-                time.sleep(0.01)
-            result = lock.acquire()  # Block while we receive a signal.
-            self.assertTrue(self.sig_recvd)
-            self.assertTrue(result)
+
+            with support.wait_threads_exit():
+                thread.start_new_thread(other_thread, ())
+                # Wait until we can't acquire it without blocking...
+                while lock.acquire(blocking=False):
+                    lock.release()
+                    time.sleep(0.01)
+                result = lock.acquire()  # Block while we receive a signal.
+                self.assertTrue(self.sig_recvd)
+                self.assertTrue(result)
         finally:
             signal.signal(signal.SIGUSR1, old_handler)
 
@@ -193,19 +200,20 @@ class ThreadSignals(unittest.TestCase):
                     os.kill(process_pid, signal.SIGUSR1)
                 done.release()
 
-            # Send the signals from the non-main thread, since the main thread
-            # is the only one that can process signals.
-            thread.start_new_thread(send_signals, ())
-            timed_acquire()
-            # Wait for thread to finish
-            done.acquire()
-            # This allows for some timing and scheduling imprecision
-            self.assertLess(self.end - self.start, 2.0)
-            self.assertGreater(self.end - self.start, 0.3)
-            # If the signal is received several times before PyErr_CheckSignals()
-            # is called, the handler will get called less than 40 times. Just
-            # check it's been called at least once.
-            self.assertGreater(self.sigs_recvd, 0)
+            with support.wait_threads_exit():
+                # Send the signals from the non-main thread, since the main thread
+                # is the only one that can process signals.
+                thread.start_new_thread(send_signals, ())
+                timed_acquire()
+                # Wait for thread to finish
+                done.acquire()
+                # This allows for some timing and scheduling imprecision
+                self.assertLess(self.end - self.start, 2.0)
+                self.assertGreater(self.end - self.start, 0.3)
+                # If the signal is received several times before PyErr_CheckSignals()
+                # is called, the handler will get called less than 40 times. Just
+                # check it's been called at least once.
+                self.assertGreater(self.sigs_recvd, 0)
         finally:
             signal.signal(signal.SIGUSR1, old_handler)
 
@@ -219,7 +227,7 @@ def test_main():
 
     oldsigs = registerSignals(handle_signals, handle_signals, handle_signals)
     try:
-        run_unittest(ThreadSignals)
+        support.run_unittest(ThreadSignals)
     finally:
         registerSignals(*oldsigs)