| // Licensed to the Apache Software Foundation (ASF) under one |
| // or more contributor license agreements. See the NOTICE file |
| // distributed with this work for additional information |
| // regarding copyright ownership. The ASF licenses this file |
| // to you under the Apache License, Version 2.0 (the |
| // "License"); you may not use this file except in compliance |
| // with the License. You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, |
| // software distributed under the License is distributed on an |
| // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| // KIND, either express or implied. See the License for the |
| // specific language governing permissions and limitations |
| // under the License. |
| |
| #ifndef KUDU_CFILE_BLOCK_HANDLE_H |
| #define KUDU_CFILE_BLOCK_HANDLE_H |
| |
| #include <memory> |
| |
| #include <boost/variant/get.hpp> |
| #include <boost/variant/variant.hpp> |
| |
| #include "kudu/cfile/block_cache.h" |
| #include "kudu/common/rowblock_memory.h" |
| #include "kudu/gutil/ref_counted.h" |
| |
| namespace kudu { |
| namespace cfile { |
| |
| // When blocks are read, they are sometimes resident in the block cache, and sometimes skip the |
| // block cache. In the case that they came from the cache, we just need to dereference them when |
| // they stop being used. In the case that they didn't come from cache, we need to actually free |
| // the underlying data. |
| // |
| // NOTE ON REFERENCE COUNTING |
| // --------------------------- |
| // Note that the BlockHandle itself may refer to a BlockCacheHandle, which itself is |
| // reference-counted. When all of the references to a BlockHandle go out of scope, it |
| // results in decrementing the BlockCacheHandle's reference count. |
| class BlockHandle final : public RefCountedThreadSafe<BlockHandle> { |
| public: |
| static scoped_refptr<BlockHandle> WithOwnedData(const Slice& data) { |
| return { new BlockHandle(data) }; |
| } |
| |
| static scoped_refptr<BlockHandle> WithDataFromCache(BlockCacheHandle handle) { |
| return { new BlockHandle(std::move(handle)) }; |
| } |
| |
| Slice data() const { return data_; } |
| |
| scoped_refptr<BlockHandle> SubrangeBlock(size_t offset, size_t len) { |
| return { new BlockHandle(this, offset, len) }; |
| } |
| |
| protected: |
| friend class RefCountedThreadSafe<BlockHandle>; |
| |
| // Marker to indicate that this object isn't initialized (owns no data). |
| struct Uninitialized {}; |
| // Marker that the handle directly owns the data in 'data_', rather than referring |
| // to data in the block cache or to another BlockHandle. |
| struct OwnedData {}; |
| |
| ~BlockHandle() { |
| Reset(); |
| } |
| // Constructor for owned data. |
| explicit BlockHandle(Slice data) |
| : data_(data), |
| ref_(OwnedData{}) { |
| } |
| |
| explicit BlockHandle(BlockCacheHandle dblk_data) |
| : data_(dblk_data.data()), |
| ref_(std::move(dblk_data)) { |
| } |
| |
| BlockHandle(scoped_refptr<BlockHandle> other, size_t offset, size_t len) |
| : data_(other->data()), |
| ref_(std::move(other)) { |
| data_.remove_prefix(offset); |
| data_.truncate(len); |
| } |
| |
| void Reset() { |
| if (boost::get<OwnedData>(&ref_) != nullptr) { |
| delete [] data_.data(); |
| } |
| data_ = ""; |
| ref_ = Uninitialized{}; |
| } |
| |
| Slice data_; |
| boost::variant<Uninitialized, OwnedData, BlockCacheHandle, scoped_refptr<BlockHandle>> ref_; |
| |
| DISALLOW_COPY_AND_ASSIGN(BlockHandle); |
| }; |
| |
| } // namespace cfile |
| } // namespace kudu |
| #endif |