fix crash in sample (#2904)

Co-authored-by: Shylock Hg <33566796+Shylock-Hg@users.noreply.github.com>

src/common/algorithm/ReservoirSampling.h

@@ -37,7 +37,13 @@ class ReservoirSampling final {
     return false;
   }
 
-  std::vector<T>&& samples() && { return std::move(samples_); }
+  std::vector<T> samples() {
+    auto result = std::move(samples_);
+    samples_.clear();
+    samples_.reserve(num_);
+    cnt_ = 0;
+    return result;
+  }
 
  private:
   std::vector<T> samples_;

src/common/algorithm/test/ReservoirSamplingTest.cpp

@@ -18,7 +18,7 @@ TEST(ReservoirSamplingTest, Sample) {
       sampler.sampling(std::move(i));
     }
 
-    auto result = std::move(sampler).samples();
+    auto result = sampler.samples();
     EXPECT_EQ(5, result.size());
     for (auto i : result) {
       EXPECT_LE(0, i);
@@ -27,16 +27,18 @@ TEST(ReservoirSamplingTest, Sample) {
   }
   {
     ReservoirSampling<int64_t> sampler(5);
-    std::vector<int64_t> sampleSpace = {0, 1, 2};
-    for (auto i : sampleSpace) {
-      sampler.sampling(std::move(i));
-    }
+    for (size_t count = 0; count < 10; count++) {
+      std::vector<int64_t> sampleSpace = {0, 1, 2};
+      for (auto i : sampleSpace) {
+        sampler.sampling(std::move(i));
+      }
 
-    auto result = std::move(sampler).samples();
-    EXPECT_EQ(3, result.size());
-    EXPECT_EQ(0, result[0]);
-    EXPECT_EQ(1, result[1]);
-    EXPECT_EQ(2, result[2]);
+      auto result = sampler.samples();
+      EXPECT_EQ(3, result.size());
+      EXPECT_EQ(0, result[0]);
+      EXPECT_EQ(1, result[1]);
+      EXPECT_EQ(2, result[2]);
+    }
   }
 }
 }  // namespace algorithm

src/storage/exec/GetNeighborsNode.h

@@ -160,7 +160,7 @@ class GetNeighborsSampleNode : public GetNeighborsNode {
     }
 
     RowReaderWrapper reader;
-    auto samples = std::move(*sampler_).samples();
+    auto samples = sampler_->samples();
     for (auto& sample : samples) {
       auto columnIdx = std::get<4>(sample);
       // add edge prop value to the target column