Fix PinnableSlice move assignment

Summary:
After move assignment, we need to re-initialized the moved PinnableSlice.

Also update blob_db_impl.cc to not reuse the moved PinnableSlice since it is supposed to be in an undefined state after move.
Closes https://github.com/facebook/rocksdb/pull/3127

Differential Revision: D6238585

Pulled By: yiwu-arbug

fbshipit-source-id: bd99f2e37406c4f7de160c7dee6a2e8126bc224e

include/rocksdb/slice.h

@@ -150,6 +150,10 @@ class PinnableSlice : public Slice, public Cleanable {
       } else {
         buf_ = other.buf_;
       }
+      // Re-initialize the other PinnablaeSlice.
+      other.self_space_.clear();
+      other.buf_ = &other.self_space_;
+      other.pinned_ = false;
     }
     return *this;
   }

util/slice_test.cc

@@ -47,6 +47,7 @@ TEST_F(SliceTest, PinnableSliceMoveConstruct) {
     ASSERT_EQ("bar", s2->ToString());
     s2->RegisterCleanup(BumpCounter, &orig_cleanup, nullptr);
     *s2 = std::move(*s1);
+    ASSERT_FALSE(s1->IsPinned());
     ASSERT_EQ("foo", s2->ToString());
     ASSERT_EQ(1, orig_cleanup);
     ASSERT_EQ(0, moved_cleanup);

utilities/blob_db/blob_db_impl.cc

@@ -1226,13 +1226,16 @@ Status BlobDBImpl::Get(const ReadOptions& read_options,
 
   Status s;
   bool is_blob_index = false;
-  s = db_impl_->GetImpl(ro, column_family, key, value, nullptr /*value_found*/,
-                        nullptr /*read_callback*/, &is_blob_index);
+  PinnableSlice index_entry;
+  s = db_impl_->GetImpl(ro, column_family, key, &index_entry,
+                        nullptr /*value_found*/, nullptr /*read_callback*/,
+                        &is_blob_index);
   TEST_SYNC_POINT("BlobDBImpl::Get:AfterIndexEntryGet:1");
   TEST_SYNC_POINT("BlobDBImpl::Get:AfterIndexEntryGet:2");
   if (s.ok()) {
-    if (is_blob_index) {
-      PinnableSlice index_entry = std::move(*value);
+    if (!is_blob_index) {
+      *value = std::move(index_entry);
+    } else {
       s = GetBlobValue(key, index_entry, value);
     }
   }