add cfh deletion started listener

Summary: add ColumnFamilyHandleDeletionStarted listener which can be called when user deletes handler.

Test Plan: ./listener_test

Reviewers: yiwu, IslamAbdelRahman, sdong, andrewkr

Reviewed By: andrewkr

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D60717

db/column_family.cc

@@ -45,6 +45,11 @@ ColumnFamilyHandleImpl::ColumnFamilyHandleImpl(
 
 ColumnFamilyHandleImpl::~ColumnFamilyHandleImpl() {
   if (cfd_ != nullptr) {
+#ifndef ROCKSDB_LITE
+    for (auto& listener : cfd_->ioptions()->listeners) {
+      listener->OnColumnFamilyHandleDeletionStarted(this);
+    }
+#endif  // ROCKSDB_LITE
     // Job id == 0 means that this is not our background process, but rather
     // user thread
     JobContext job_context(0);

db/listener_test.cc

@@ -754,8 +754,43 @@ TEST_F(EventListenerTest, MemTableSealedListenerTest) {
     ASSERT_OK(Flush());
   }
 }
-} // namespace rocksdb
 
+class ColumnFamilyHandleDeletionStartedListener : public EventListener {
+ private:
+  std::vector<std::string> cfs_;
+  int counter;
+
+ public:
+  explicit ColumnFamilyHandleDeletionStartedListener(
+      const std::vector<std::string>& cfs)
+      : cfs_(cfs), counter(0) {
+    cfs_.insert(cfs_.begin(), kDefaultColumnFamilyName);
+  }
+  void OnColumnFamilyHandleDeletionStarted(
+      ColumnFamilyHandle* handle) override {
+    ASSERT_EQ(cfs_[handle->GetID()], handle->GetName());
+    counter++;
+  }
+  int getCounter() { return counter; }
+};
+
+TEST_F(EventListenerTest, ColumnFamilyHandleDeletionStartedListenerTest) {
+  std::vector<std::string> cfs{"pikachu", "eevee", "Mewtwo"};
+  auto listener =
+      std::make_shared<ColumnFamilyHandleDeletionStartedListener>(cfs);
+  Options options;
+  options.create_if_missing = true;
+  options.listeners.push_back(listener);
+  CreateAndReopenWithCF(cfs, options);
+  ASSERT_EQ(handles_.size(), 4);
+  delete handles_[3];
+  delete handles_[2];
+  delete handles_[1];
+  handles_.resize(1);
+  ASSERT_EQ(listener->getCounter(), 3);
+}
+
+}  // namespace rocksdb
 
 #endif  // ROCKSDB_LITE
 

include/rocksdb/listener.h

@@ -18,6 +18,7 @@ typedef std::unordered_map<std::string, std::shared_ptr<const TableProperties>>
     TablePropertiesCollection;
 
 class DB;
+class ColumnFamilyHandle;
 class Status;
 struct CompactionJobStats;
 enum CompressionType : unsigned char;
@@ -279,6 +280,17 @@ class EventListener {
   virtual void OnMemTableSealed(
     const MemTableInfo& /*info*/) {}
 
+  // A call-back function for RocksDB which will be called before
+  // a column family handle is deleted.
+  //
+  // Note that the this function must be implemented in a way such that
+  // it should not run for an extended period of time before the function
+  // returns.  Otherwise, RocksDB may be blocked.
+  // @param handle is a pointer to the column family handle to be deleted
+  // which will become a dangling pointer after the deletion.
+  virtual void OnColumnFamilyHandleDeletionStarted(ColumnFamilyHandle* handle) {
+  }
+
   virtual ~EventListener() {}
 };