fix edge case and docstring in minddata multiprocessing shared memory code

mindspore/ccsrc/minddata/dataset/core/config_manager.cc

@@ -50,7 +50,7 @@ ConfigManager::ConfigManager()
       num_cpu_threads_(std::thread::hardware_concurrency()),
       auto_num_workers_num_shards_(1),
       auto_worker_config_(0),
-      enable_shared_mem_(false) {
+      enable_shared_mem_(true) {
   num_cpu_threads_ = num_cpu_threads_ > 0 ? num_cpu_threads_ : std::numeric_limits<uint16_t>::max();
   num_parallel_workers_ = num_parallel_workers_ < num_cpu_threads_ ? num_parallel_workers_ : num_cpu_threads_;
   auto env_cache_host = std::getenv("MS_CACHE_HOST");

mindspore/dataset/core/config.py

@@ -381,7 +381,7 @@ def get_enable_shared_mem():
 
 
     Returns:
-        bool, the state of shared mem enabled variable (default: True).
+        bool, the state of shared mem enabled variable (default=True).
     """
     return _config.get_enable_shared_mem()
 

mindspore/dataset/engine/queue.py

@@ -66,7 +66,7 @@ class _SharedQueue(multiprocessing.queues.Queue):
             if (isinstance(r, np.ndarray) and r.size > self.min_shared_mem and
                     start_bytes + r.nbytes < self.seg_size):
                 ##need to convert start_bytes to offset in array
-                start_offset = start_bytes // r.dtype.itemsize
+                start_offset = start_bytes
                 dest = np.ndarray(r.shape, r.dtype, buffer=self.shm_list[self.seg_pos].get_obj(), offset=start_offset)
                 np.copyto(dest, r)
                 byte = r.nbytes
@@ -101,7 +101,7 @@ class _SharedQueue(multiprocessing.queues.Queue):
                 byte = x[2]
                 dtype = x[3]
                 shape = x[4]
-                start_offset = start_bytes // dtype.itemsize
+                start_offset = start_bytes
                 b = self.shm_list[seg_pos]
                 data = np.ndarray(shape, dtype, buffer=b.get_obj(), offset=start_offset)
                 start_bytes += byte

tests/ut/python/dataset/test_datasets_generator.py

@@ -36,6 +36,15 @@ class DatasetGenerator:
 
     def __len__(self):
         return 10
+class DatasetGeneratorLarge:
+    def __init__(self):
+        self.data = np.array(range(4000))
+
+    def __getitem__(self, item):
+        return (self.data + item, self.data *10)
+
+    def __len__(self):
+        return 10
 
 
 def test_generator_0():
@@ -503,6 +512,26 @@ def test_generator_18():
         golden = np.array([i * 5])
         np.testing.assert_array_equal(item["out0"], golden)
 
+def test_generator_19():
+    """
+    Test multiprocessing flag with 2 different large columns
+    """
+    logger.info("Test map column order when input_columns is None.")
+
+    # apply dataset operations
+    data1 = ds.GeneratorDataset(DatasetGeneratorLarge(), ["col0", "col1"], python_multiprocessing=True, shuffle=False)
+
+    # Expected column order is |out0|col1|
+    i = 0
+    for item in data1.create_tuple_iterator(num_epochs=1, output_numpy=True):
+        assert len(item) == 2
+        golden = np.array(range(4000)) + i
+        np.testing.assert_array_equal(item[0], golden)
+        golden = np.array(range(4000)) * 10
+        np.testing.assert_array_equal(item[1], golden)
+        i = i + 1
+
+
 def test_generator_error_1():
     def generator_np():
         for i in range(64):
@@ -804,6 +833,7 @@ if __name__ == "__main__":
     test_generator_16()
     test_generator_17()
     test_generator_18()
+    test_generator_19()
     test_generator_error_1()
     test_generator_error_2()
     test_generator_error_3()

tests/ut/python/dataset/test_pyfunc.py

@@ -341,6 +341,7 @@ if __name__ == "__main__":
     test_case_7()
     test_case_8()
     test_case_9()
+    test_case_10()
     test_pyfunc_implicit_compose()
     test_pyfunc_exception()
     skip_test_pyfunc_exception_multiprocess()