fix dataloader exit hang when join re-enter (#32827)

* fix dataloader exit hang when join re-enter. test=develop

python/paddle/fluid/dataloader/dataloader_iter.py

@@ -289,10 +289,14 @@ class _DataLoaderIterMultiProcess(_DataLoaderIterBase):
 
         # if user exit python program when dataloader is still
         # iterating, resource may no release safely, so we
-        # add __del__ function to to CleanupFuncRegistrar
-        # to make sure __del__ is always called when program
+        # add _shutdown_on_exit function to to CleanupFuncRegistrar
+        # to make sure _try_shutdown_all is always called when program
         # exit for resoure releasing safely
-        CleanupFuncRegistrar.register(self.__del__)
+        # worker join may hang for in _try_shutdown_all call in atexit
+        # for main process is in atexit state in some OS, so we add
+        # timeout=1 for shutdown function call in atexit, for shutdown
+        # function call in __del__, we keep it as it is
+        CleanupFuncRegistrar.register(self._shutdown_on_exit)
 
     def _init_workers(self):
         # multiprocess worker and indice queue list initial as empty
@@ -363,7 +367,7 @@ class _DataLoaderIterMultiProcess(_DataLoaderIterBase):
             self._indices_queues[worker_id].put(None)
             self._worker_status[worker_id] = False
 
-    def _try_shutdown_all(self):
+    def _try_shutdown_all(self, timeout=None):
         if not self._shutdown:
             try:
                 self._exit_thread_expectedly()
@@ -376,11 +380,12 @@ class _DataLoaderIterMultiProcess(_DataLoaderIterBase):
                 for i in range(self._num_workers):
                     self._shutdown_worker(i)
 
-                for w in self._workers:
-                    w.join()
-                for q in self._indices_queues:
-                    q.cancel_join_thread()
-                    q.close()
+                if not self._shutdown:
+                    for w in self._workers:
+                        w.join(timeout)
+                    for q in self._indices_queues:
+                        q.cancel_join_thread()
+                        q.close()
             finally:
                 core._erase_process_pids(id(self))
                 self._shutdown = True
@@ -560,6 +565,9 @@ class _DataLoaderIterMultiProcess(_DataLoaderIterBase):
     def __del__(self):
         self._try_shutdown_all()
 
+    def _shutdown_on_exit(self):
+        self._try_shutdown_all(1)
+
     def __next__(self):
         try:
             # _batches_outstanding here record the total batch data number