bpo-45310: Fix parrallel shared memory tests (GH-28661) (GH-28979)

Add a PID to names of POSIX shared memory objects to allow
running multiprocessing tests (test_multiprocessing_fork,
test_multiprocessing_spawn, etc) in parallel.

(cherry picked from commit eb4495e)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Author: vstinner

Lib/test/_test_multiprocessing.py

@@ -3749,12 +3749,19 @@ def _attach_existing_shmem_then_write(shmem_name_or_obj, binary_data):
         local_sms.buf[:len(binary_data)] = binary_data
         local_sms.close()
 
+    def _new_shm_name(self, prefix):
+        # Add a PID to the name of a POSIX shared memory object to allow
+        # running multiprocessing tests (test_multiprocessing_fork,
+        # test_multiprocessing_spawn, etc) in parallel.
+        return prefix + str(os.getpid())
+
     def test_shared_memory_basics(self):
-        sms = shared_memory.SharedMemory('test01_tsmb', create=True, size=512)
+        name_tsmb = self._new_shm_name('test01_tsmb')
+        sms = shared_memory.SharedMemory(name_tsmb, create=True, size=512)
         self.addCleanup(sms.unlink)
 
         # Verify attributes are readable.
-        self.assertEqual(sms.name, 'test01_tsmb')
+        self.assertEqual(sms.name, name_tsmb)
         self.assertGreaterEqual(sms.size, 512)
         self.assertGreaterEqual(len(sms.buf), sms.size)
 
@@ -3763,12 +3770,12 @@ def test_shared_memory_basics(self):
         self.assertEqual(sms.buf[0], 42)
 
         # Attach to existing shared memory segment.
-        also_sms = shared_memory.SharedMemory('test01_tsmb')
+        also_sms = shared_memory.SharedMemory(name_tsmb)
         self.assertEqual(also_sms.buf[0], 42)
         also_sms.close()
 
         # Attach to existing shared memory segment but specify a new size.
-        same_sms = shared_memory.SharedMemory('test01_tsmb', size=20*sms.size)
+        same_sms = shared_memory.SharedMemory(name_tsmb, size=20*sms.size)
         self.assertLess(same_sms.size, 20*sms.size)  # Size was ignored.
         same_sms.close()
 
@@ -3779,17 +3786,17 @@ def test_shared_memory_basics(self):
             # manages unlinking on its own and unlink() does nothing).
             # True release of shared memory segment does not necessarily
             # happen until process exits, depending on the OS platform.
+            name_dblunlink = self._new_shm_name('test01_dblunlink')
+            sms_uno = shared_memory.SharedMemory(
+                name_dblunlink,
+                create=True,
+                size=5000
+            )
             with self.assertRaises(FileNotFoundError):
-                sms_uno = shared_memory.SharedMemory(
-                    'test01_dblunlink',
-                    create=True,
-                    size=5000
-                )
-
                 try:
                     self.assertGreaterEqual(sms_uno.size, 5000)
 
-                    sms_duo = shared_memory.SharedMemory('test01_dblunlink')
+                    sms_duo = shared_memory.SharedMemory(name_dblunlink)
                     sms_duo.unlink()  # First shm_unlink() call.
                     sms_duo.close()
                     sms_uno.close()
@@ -3801,7 +3808,7 @@ def test_shared_memory_basics(self):
             # Attempting to create a new shared memory segment with a
             # name that is already in use triggers an exception.
             there_can_only_be_one_sms = shared_memory.SharedMemory(
-                'test01_tsmb',
+                name_tsmb,
                 create=True,
                 size=512
             )
@@ -3815,7 +3822,7 @@ def test_shared_memory_basics(self):
             # case of MacOS/darwin, requesting a smaller size is disallowed.
             class OptionalAttachSharedMemory(shared_memory.SharedMemory):
                 _flags = os.O_CREAT | os.O_RDWR
-            ok_if_exists_sms = OptionalAttachSharedMemory('test01_tsmb')
+            ok_if_exists_sms = OptionalAttachSharedMemory(name_tsmb)
             self.assertEqual(ok_if_exists_sms.size, sms.size)
             ok_if_exists_sms.close()
 
@@ -4003,10 +4010,11 @@ def test_shared_memory_ShareableList_basics(self):
             self.assertEqual(sl.count(b'adios'), 0)
 
         # Exercise creating a duplicate.
-        sl_copy = shared_memory.ShareableList(sl, name='test03_duplicate')
+        name_duplicate = self._new_shm_name('test03_duplicate')
+        sl_copy = shared_memory.ShareableList(sl, name=name_duplicate)
         try:
             self.assertNotEqual(sl.shm.name, sl_copy.shm.name)
-            self.assertEqual('test03_duplicate', sl_copy.shm.name)
+            self.assertEqual(name_duplicate, sl_copy.shm.name)
             self.assertEqual(list(sl), list(sl_copy))
             self.assertEqual(sl.format, sl_copy.format)
             sl_copy[-1] = 77