Method ReadFromMemBuffer

be/src/runtime/io/disk-file.h:414–426

Read the spilled data from the memory buffer. Caller should hold the physical file lock of the disk file in case the object is destroyed. Also, caller should guarantee the buffer won't be released during reading, it is good for the caller to have the lock of the read buffer block.

  // destroyed. Also, caller should guarantee the buffer won't be released during reading,
  // it is good for the caller to have the lock of the read buffer block.
  Status ReadFromMemBuffer(int64_t offset_to_file, int64_t len, uint8_t* dst,
      const boost::shared_lock<boost::shared_mutex>& file_lock) {
    DCHECK(file_lock.mutex() == &physical_file_lock_ && file_lock.owns_lock());
    int64_t idx = GetReadBufferIndex(offset_to_file);
    DCheckReadBufferIdx(idx);
    uint8_t* read_buffer_block = read_buffer_->read_buffer_blocks_[idx]->data();
    DCHECK(read_buffer_block != nullptr);
    int64_t offset_to_block = offset_to_file - GetReadBuffStartOffset(idx);
    DCHECK_GE(offset_to_block, 0);
    DCHECK_GE(GetReadBuffActualSize(idx), offset_to_block + len);
    memcpy(dst, read_buffer_block + offset_to_block, len);
    return Status::OK();
  }

  // Helper function to allocate the memory for a reading buffer block.
  // Caller should hold both physical_file_lock_ and the lock of the read buffer block.