1 files changed, 147 insertions, 0 deletions
diff --git a/src/rocksdb/db/merge_context.h b/src/rocksdb/db/merge_context.h
new file mode 100644
index 000000000..8a7b07290
--- /dev/null
+++ b/src/rocksdb/db/merge_context.h
@@ -0,0 +1,147 @@
+//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+//
+#pragma once
+#include <algorithm>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "rocksdb/slice.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+const std::vector<Slice> empty_operand_list;
+
+// The merge context for merging a user key.
+// When doing a Get(), DB will create such a class and pass it when
+// issuing Get() operation to memtables and version_set. The operands
+// will be fetched from the context when issuing partial of full merge.
+class MergeContext {
+ public:
+  // Clear all the operands
+  void Clear() {
+    if (operand_list_) {
+      operand_list_->clear();
+      copied_operands_->clear();
+    }
+  }
+
+  // Push a merge operand
+  void PushOperand(const Slice& operand_slice, bool operand_pinned = false) {
+    Initialize();
+    SetDirectionBackward();
+
+    if (operand_pinned) {
+      operand_list_->push_back(operand_slice);
+    } else {
+      // We need to have our own copy of the operand since it's not pinned
+      copied_operands_->emplace_back(
+          new std::string(operand_slice.data(), operand_slice.size()));
+      operand_list_->push_back(*copied_operands_->back());
+    }
+  }
+
+  // Push back a merge operand
+  void PushOperandBack(const Slice& operand_slice,
+                       bool operand_pinned = false) {
+    Initialize();
+    SetDirectionForward();
+
+    if (operand_pinned) {
+      operand_list_->push_back(operand_slice);
+    } else {
+      // We need to have our own copy of the operand since it's not pinned
+      copied_operands_->emplace_back(
+          new std::string(operand_slice.data(), operand_slice.size()));
+      operand_list_->push_back(*copied_operands_->back());
+    }
+  }
+
+  // return total number of operands in the list
+  size_t GetNumOperands() const {
+    if (!operand_list_) {
+      return 0;
+    }
+    return operand_list_->size();
+  }
+
+  // Get the operand at the index.
+  Slice GetOperand(int index) const {
+    assert(operand_list_);
+
+    SetDirectionForward();
+    return (*operand_list_)[index];
+  }
+
+  // Same as GetOperandsDirectionForward
+  //
+  // Note that the returned reference is only good until another call
+  // to this MergeContext.  If the returned value is needed for longer,
+  // a copy must be made.
+  const std::vector<Slice>& GetOperands() const {
+    return GetOperandsDirectionForward();
+  }
+
+  // Return all the operands in the order as they were merged (passed to
+  // FullMerge or FullMergeV2)
+  //
+  // Note that the returned reference is only good until another call
+  // to this MergeContext.  If the returned value is needed for longer,
+  // a copy must be made.
+  const std::vector<Slice>& GetOperandsDirectionForward() const {
+    if (!operand_list_) {
+      return empty_operand_list;
+    }
+
+    SetDirectionForward();
+    return *operand_list_;
+  }
+
+  // Return all the operands in the reversed order relative to how they were
+  // merged (passed to FullMerge or FullMergeV2)
+  //
+  // Note that the returned reference is only good until another call
+  // to this MergeContext.  If the returned value is needed for longer,
+  // a copy must be made.
+  const std::vector<Slice>& GetOperandsDirectionBackward() const {
+    if (!operand_list_) {
+      return empty_operand_list;
+    }
+
+    SetDirectionBackward();
+    return *operand_list_;
+  }
+
+ private:
+  void Initialize() {
+    if (!operand_list_) {
+      operand_list_.reset(new std::vector<Slice>());
+      copied_operands_.reset(new std::vector<std::unique_ptr<std::string>>());
+    }
+  }
+
+  void SetDirectionForward() const {
+    if (operands_reversed_ == true) {
+      std::reverse(operand_list_->begin(), operand_list_->end());
+      operands_reversed_ = false;
+    }
+  }
+
+  void SetDirectionBackward() const {
+    if (operands_reversed_ == false) {
+      std::reverse(operand_list_->begin(), operand_list_->end());
+      operands_reversed_ = true;
+    }
+  }
+
+  // List of operands
+  mutable std::unique_ptr<std::vector<Slice>> operand_list_;
+  // Copy of operands that are not pinned.
+  std::unique_ptr<std::vector<std::unique_ptr<std::string>>> copied_operands_;
+  mutable bool operands_reversed_ = true;
+};
+
+}  // namespace ROCKSDB_NAMESPACE