Added example for multiple iterator

Added new testcase for multi iterator

Addressing review

Fixed typo

mindspore/ccsrc/dataset/engine/datasetops/barrier_op.cc

@@ -65,8 +65,8 @@ Status BarrierOp::operator()() {
   TaskManager::FindMe()->Post();
 
   // create child iterator, right now this barrier is a pipeline operator
-  int32_t worker_id = 0;
-  int32_t child_idx = 0;
+  const int32_t worker_id = 0;
+  const int32_t child_idx = 0;
   child_iterator_ = std::make_unique<ChildIterator>(this, worker_id, child_idx);
 
   // Loop until eof is true

mindspore/dataset/engine/datasets.py

@@ -920,7 +920,7 @@ class Dataset:
     def sync_update(self, condition_name, num_batch=None, data=None):
         """
         condition_name (str): The condition name that is used to toggle sending next row
-        step_size (int or None): The number of steps(rows) that are released
+        num_batch (int or None): The number of batches(rows) that are released
                          when pass_rows is None, will update the same number as sync_wait specified
         data (dict or None): The data passed to the callback
         """

tests/ut/python/dataset/test_sync_wait.py

@@ -107,6 +107,7 @@ def test_two_sync():
         if count % 2 == 0:
             dataset.sync_update(condition_name="every 2 batches")
 
+
 def test_sync_epoch():
     """
     Test sync wait with epochs: test sync with epochs in dataset pipeline  
@@ -130,6 +131,34 @@ def test_sync_epoch():
             dataset.sync_update(condition_name="policy", data=data)
 
 
+def test_multiple_iterators(): 
+    """
+    Test sync wait with multiple iterators: will start multiple 
+    """
+    logger.info("test_sync_epoch")
+    batch_size = 30
+    dataset = ds.GeneratorDataset(gen, column_names=["input"])
+
+    aug = Augment(0)
+    dataset = dataset.sync_wait(condition_name="policy", callback=aug.update)
+    dataset = dataset.map(input_columns=["input"], operations=[aug.preprocess])
+    dataset = dataset.batch(batch_size, drop_remainder=True)
+    # 2nd dataset 
+    dataset2 = ds.GeneratorDataset(gen, column_names=["input"])
+
+    aug = Augment(0)
+    dataset2 = dataset2.sync_wait(condition_name="policy", callback=aug.update)
+    dataset2 = dataset2.map(input_columns=["input"], operations=[aug.preprocess])
+    dataset2 = dataset2.batch(batch_size, drop_remainder=True)
+
+    for item1, item2 in zip(dataset.create_dict_iterator(), dataset2.create_dict_iterator()):
+        assert (item1["input"][0] == item2["input"][0]) 
+        data1 = {"loss": item1["input"][0]}
+        data2 = {"loss": item2["input"][0]}
+        dataset.sync_update(condition_name="policy", data=data1)
+        dataset2.sync_update(condition_name="policy", data=data2)
+
+
 def test_sync_exception_01():
     """
     Test sync: with shuffle in sync mode 
@@ -179,4 +208,5 @@ if __name__ == "__main__":
     test_two_sync()
     test_sync_exception_01()
     test_sync_exception_02()
-    test_sync_epoch()
+    test_sync_epoch()
+    test_multiple_iterators()