!12154 Fix samplers bugs

From: @hfarahat
Reviewed-by: @heleiwang,@liucunwei
Signed-off-by: @liucunwei

mindspore/ccsrc/minddata/dataset/engine/datasetops/source/generator_op.cc

@@ -193,9 +193,9 @@ Status GeneratorOp::operator()() {
   TaskManager::FindMe()->Post();
   RETURN_IF_NOT_OK(wp_.Register(tree_->AllTasks()));
   std::unique_ptr<DataBuffer> fetched_buffer;
+  int64_t num_rows_sampled = sampler_ ? sampler_->CalculateNumSamples(num_rows_) : num_rows_;
   RETURN_IF_NOT_OK(Init());
 
-  int64_t num_rows_sampled = sampler_ ? sampler_->CalculateNumSamples(num_rows_) : num_rows_;
   bool eof = false;
   while (!eof) {
     // Create new buffer each iteration

mindspore/ccsrc/minddata/dataset/engine/datasetops/source/sampler/distributed_sampler.cc

@@ -184,7 +184,6 @@ int64_t DistributedSamplerRT::CalculateNumSamples(int64_t num_rows) {
     if (device_id_ < remainder) shard_size++;
     if (device_id_ < offset_) shard_size--;
   } else {
-    offset_ = 0;
     shard_size = (child_num_rows + num_devices_ - 1) / num_devices_;
   }
   // add 1 to an empty shard

mindspore/ccsrc/minddata/dataset/engine/ir/datasetops/source/generator_node.cc

@@ -42,7 +42,12 @@ GeneratorNode::GeneratorNode(py::function generator_function, const std::vector<
 
 GeneratorNode::GeneratorNode(py::function generator_function, const std::shared_ptr<SchemaObj> &schema,
                              int64_t source_len, std::shared_ptr<SamplerObj> sampler)
-    : MappableSourceNode(), generator_function_(generator_function), schema_(schema), reset_ancestor_(nullptr) {}
+    : MappableSourceNode(),
+      generator_function_(generator_function),
+      schema_(schema),
+      reset_ancestor_(nullptr),
+      sampler_(std::move(sampler)),
+      source_len_(source_len) {}
 
 std::shared_ptr<DatasetNode> GeneratorNode::Copy() {
   std::shared_ptr<GeneratorNode> node;

mindspore/dataset/engine/datasets.py

@@ -2233,6 +2233,7 @@ _GLOBAL_PYFUNC_LIST = []
 _OP_NAME = dict()
 _OP_PROCESS = dict()
 
+
 # Pyfunc worker init function
 # Python multiprocessing library forbid sending lambda function through pipe.
 # This init function allow us to add all Python function to a global collection and then fork afterwards.
@@ -3781,6 +3782,8 @@ class GeneratorDataset(MappableDataset):
             try:
                 new_op.sampler = None
                 new_op.sample_fn = sample_fn
+                new_op.source_len = min(new_op.source_len,
+                                        new_op.num_samples) if new_op.num_samples is not None else new_op.source_len
                 iter(self.source)
             except TypeError:
                 # Use generator function if input callable