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https://issues.apache.org/jira/browse/SINGA-205?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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wangwei closed SINGA-205.
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Resolution: Fixed
> Enable slice and concatenate operations for Tensor objects
> ----------------------------------------------------------
>
> Key: SINGA-205
> URL: https://issues.apache.org/jira/browse/SINGA-205
> Project: Singa
> Issue Type: New Feature
> Reporter: wangwei
> Assignee: wangwei
>
> Slice and concatenate operations are typical array operations, and are
> necessary to support some models, e.g., GoogleLeNet.
> For this ticket, we are going to implement the two operations to support 1D
> and 2D tensors. The following functions would be implemented,
> 1. SliceRows(Tensor, start, end), the returned tensor shares the memory with
> the origin tensor.
> 2. CopyRows(Tensor, start, end), CopyColumns(Tensor, start, end) the returned
> tensor copies values from the original tensor
> 3. ConcatenateRows(vector<Tensor>) and ConcatenateColumns(vector<Tensor>);
> the returned tensor copies values from the origin tensors.
> To support SliceRows, i.e., memory sharing between two tensors of different
> sizes, we need to update the Block class as
> {code}
> class Block {
> Block(void* ptr, size_t size, size_t offset=0);
> void* mutable_data() const { return data_+offset_;}
> const void* data() const { return data_+offset_;}
> private:
> void *data_;
> size_t offset_ = 0; // offset in terms of Bytes.
> shared_ptr<atomic<int>> ref_count_;
> };
> {code}
> The sub-tensors (i.e., generated from SliceRows) would have a different Block
> instance as the original tensor, but would share the internal `ref_count_`
> and `data_` fields.
> `offset_` is 0 for the original tensors, but non-zero for sub-tensors .
> atomic makes the inc and dec operations thread-safe. shared_ptr helps to free
> `ref_count_` safely.
> SliceColumns is not supported as singa::Tensor uses row major storage which
> is difficult to support SliceColumns SliceRows(). Users can use CopyColumns().
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