Fix flaky db_basic_bench caused by unreleased iterator (#10058)

Summary:
Iterator is not freed after test is done (after the main for
loop), which could cause db close failed.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10058

Test Plan:
Able to reproduce consistently with higher thread number,
like 100, make sure it passes after the fix

Reviewed By: ajkr

Differential Revision: D36685823

Pulled By: jay-zhuang

fbshipit-source-id: 4c98b8758d106bfe40cae670e689c3d284765bcf

microbench/db_basic_bench.cc

@@ -1109,9 +1109,8 @@ static void IteratorSeek(benchmark::State& state) {
     }
   }
 
-  {
-    std::unique_ptr<Iterator> iter{nullptr};
   for (auto _ : state) {
+    std::unique_ptr<Iterator> iter{nullptr};
     state.PauseTiming();
     if (!iter) {
       iter.reset(db->NewIterator(ReadOptions()));
@@ -1124,7 +1123,6 @@ static void IteratorSeek(benchmark::State& state) {
     state.ResumeTiming();
     iter->Seek(key);
   }
-  }
 
   if (state.thread_index() == 0) {
     TeardownDB(state, db, options, kg);
@@ -1202,9 +1200,8 @@ static void IteratorNext(benchmark::State& state) {
     }
   }
 
-  {
-    std::unique_ptr<Iterator> iter{nullptr};
   for (auto _ : state) {
+    std::unique_ptr<Iterator> iter{nullptr};
     state.PauseTiming();
     if (!iter) {
       iter.reset(db->NewIterator(ReadOptions()));
@@ -1218,7 +1215,6 @@ static void IteratorNext(benchmark::State& state) {
     state.ResumeTiming();
     iter->Next();
   }
-  }
 
   if (state.thread_index() == 0) {
     TeardownDB(state, db, options, kg);
@@ -1281,9 +1277,8 @@ static void IteratorNextWithPerfContext(benchmark::State& state) {
   SetPerfLevel(kEnableTime);
   get_perf_context()->EnablePerLevelPerfContext();
 
-  {
-    std::unique_ptr<Iterator> iter{nullptr};
   for (auto _ : state) {
+    std::unique_ptr<Iterator> iter{nullptr};
     state.PauseTiming();
     if (!iter) {
       iter.reset(db->NewIterator(ReadOptions()));
@@ -1298,15 +1293,12 @@ static void IteratorNextWithPerfContext(benchmark::State& state) {
     state.ResumeTiming();
 
     iter->Next();
-      user_key_comparison_count +=
-          get_perf_context()->user_key_comparison_count;
+    user_key_comparison_count += get_perf_context()->user_key_comparison_count;
     internal_key_skipped_count +=
         get_perf_context()->internal_key_skipped_count;
-      find_next_user_entry_time +=
-          get_perf_context()->find_next_user_entry_time;
+    find_next_user_entry_time += get_perf_context()->find_next_user_entry_time;
     iter_next_cpu_nanos += get_perf_context()->iter_next_cpu_nanos;
   }
-  }
 
   state.counters["user_key_comparison_count"] =
       benchmark::Counter(static_cast<double>(user_key_comparison_count),
@@ -1370,9 +1362,8 @@ static void IteratorPrev(benchmark::State& state) {
     }
   }
 
-  {
-    std::unique_ptr<Iterator> iter{nullptr};
   for (auto _ : state) {
+    std::unique_ptr<Iterator> iter{nullptr};
     state.PauseTiming();
     if (!iter) {
       iter.reset(db->NewIterator(ReadOptions()));
@@ -1386,7 +1377,6 @@ static void IteratorPrev(benchmark::State& state) {
     state.ResumeTiming();
     iter->Prev();
   }
-  }
 
   if (state.thread_index() == 0) {
     TeardownDB(state, db, options, kg);
@@ -1464,9 +1454,8 @@ static void PrefixSeek(benchmark::State& state) {
     }
   }
 
-  {
-    std::unique_ptr<Iterator> iter{nullptr};
   for (auto _ : state) {
+    std::unique_ptr<Iterator> iter{nullptr};
     state.PauseTiming();
     if (!iter) {
       iter.reset(db->NewIterator(ReadOptions()));
@@ -1478,7 +1467,6 @@ static void PrefixSeek(benchmark::State& state) {
       return;
     }
   }
-  }
 
   if (state.thread_index() == 0) {
     TeardownDB(state, db, options, kg);