Remove the use of exception in WriteBatch::Handler

Summary:
Remove the use of exception in WriteBatch::Handler.  Now the default
implementations of Put, Merge, and Delete in WriteBatch::Handler are no-op.

Test Plan:
Add three test cases in write_batch_test
./write_batch_test

Reviewers: sdong, igor

Reviewed By: sdong, igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D29835

db/write_batch.cc

@@ -48,20 +48,6 @@ WriteBatch::~WriteBatch() { }
 
 WriteBatch::Handler::~Handler() { }
 
-void WriteBatch::Handler::Put(const Slice& key, const Slice& value) {
-  // you need to either implement Put or PutCF
-  throw std::runtime_error("Handler::Put not implemented!");
-}
-
-void WriteBatch::Handler::Merge(const Slice& key, const Slice& value) {
-  throw std::runtime_error("Handler::Merge not implemented!");
-}
-
-void WriteBatch::Handler::Delete(const Slice& key) {
-  // you need to either implement Delete or DeleteCF
-  throw std::runtime_error("Handler::Delete not implemented!");
-}
-
 void WriteBatch::Handler::LogData(const Slice& blob) {
   // If the user has not specified something to do with blobs, then we ignore
   // them.

db/write_batch_test.cc

@@ -187,6 +187,39 @@ namespace {
   };
 }
 
+TEST(WriteBatchTest, MergeNotImplemented) {
+  WriteBatch batch;
+  batch.Merge(Slice("foo"), Slice("bar"));
+  ASSERT_EQ(1, batch.Count());
+  ASSERT_EQ("Merge(foo, bar)@0",
+            PrintContents(&batch));
+
+  WriteBatch::Handler handler;
+  ASSERT_OK(batch.Iterate(&handler));
+}
+
+TEST(WriteBatchTest, PutNotImplemented) {
+  WriteBatch batch;
+  batch.Put(Slice("k1"), Slice("v1"));
+  ASSERT_EQ(1, batch.Count());
+  ASSERT_EQ("Put(k1, v1)@0",
+            PrintContents(&batch));
+
+  WriteBatch::Handler handler;
+  ASSERT_OK(batch.Iterate(&handler));
+}
+
+TEST(WriteBatchTest, DeleteNotImplemented) {
+  WriteBatch batch;
+  batch.Delete(Slice("k2"));
+  ASSERT_EQ(1, batch.Count());
+  ASSERT_EQ("Delete(k2)@0",
+            PrintContents(&batch));
+
+  WriteBatch::Handler handler;
+  ASSERT_OK(batch.Iterate(&handler));
+}
+
 TEST(WriteBatchTest, Blob) {
   WriteBatch batch;
   batch.Put(Slice("k1"), Slice("v1"));

include/rocksdb/write_batch.h

@@ -105,10 +105,11 @@ class WriteBatch {
       return Status::InvalidArgument(
           "non-default column family and PutCF not implemented");
     }
-    virtual void Put(const Slice& key, const Slice& value);
+    virtual void Put(const Slice& key, const Slice& value) {}
+
     // Merge and LogData are not pure virtual. Otherwise, we would break
     // existing clients of Handler on a source code level. The default
-    // implementation of Merge simply throws a runtime exception.
+    // implementation of Merge does nothing.
     virtual Status MergeCF(uint32_t column_family_id, const Slice& key,
                            const Slice& value) {
       if (column_family_id == 0) {
@@ -118,7 +119,8 @@ class WriteBatch {
       return Status::InvalidArgument(
           "non-default column family and MergeCF not implemented");
     }
-    virtual void Merge(const Slice& key, const Slice& value);
+    virtual void Merge(const Slice& key, const Slice& value) {}
+
     // The default implementation of LogData does nothing.
     virtual void LogData(const Slice& blob);
     virtual Status DeleteCF(uint32_t column_family_id, const Slice& key) {
@@ -129,7 +131,8 @@ class WriteBatch {
       return Status::InvalidArgument(
           "non-default column family and DeleteCF not implemented");
     }
-    virtual void Delete(const Slice& key);
+    virtual void Delete(const Slice& key) {}
+
     // Continue is called by WriteBatch::Iterate. If it returns false,
     // iteration is halted. Otherwise, it continues iterating. The default
     // implementation always returns true.