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https://issues.apache.org/jira/browse/ARROW-7522?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17013926#comment-17013926
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Wes McKinney edited comment on ARROW-7522 at 1/13/20 12:02 AM:
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> the buffer of the object is not kept alive
It should be kept alive, though. This buffer is sliced by the IPC read path so
there should be many shared_ptr values referencing this buffer after the call
to {{ReadNext}} (this is the equivalent of the "base" strategy that NumPy uses,
so such additional thing is not needed here)
was (Author: wesmckinn):
> the buffer of the object is not kept alive
It should be kept alive, though. This buffer is sliced by the IPC read path so
there should be many shared_ptr values referencing this buffer after the call
to {{ReadNext}}
> [C++][Plasma] Broken Record Batch returned from a function call
> ---------------------------------------------------------------
>
> Key: ARROW-7522
> URL: https://issues.apache.org/jira/browse/ARROW-7522
> Project: Apache Arrow
> Issue Type: Bug
> Components: C++, C++ - Plasma
> Affects Versions: 0.15.1
> Environment: macOS
> Reporter: Chengxin Ma
> Priority: Minor
>
> Scenario: retrieving Record Batch from Plasma with known Object ID.
> The following code snippet works well:
> {code:java}
> int main(int argc, char **argv)
> {
> plasma::ObjectID object_id =
> plasma::ObjectID::from_binary("0FF1CE00C0FFEE00BEEF");
> // Start up and connect a Plasma client.
> plasma::PlasmaClient client;
> ARROW_CHECK_OK(client.Connect("/tmp/store"));
> plasma::ObjectBuffer object_buffer;
> ARROW_CHECK_OK(client.Get(&object_id, 1, -1, &object_buffer));
> // Retrieve object data.
> auto buffer = object_buffer.data;
> arrow::io::BufferReader buffer_reader(buffer);
> std::shared_ptr<arrow::ipc::RecordBatchReader> record_batch_stream_reader;
> ARROW_CHECK_OK(arrow::ipc::RecordBatchStreamReader::Open(&buffer_reader,
> &record_batch_stream_reader));
> std::shared_ptr<arrow::RecordBatch> record_batch;
> arrow::Status status =
> record_batch_stream_reader->ReadNext(&record_batch);
> std::cout << "record_batch->column_name(0): " <<
> record_batch->column_name(0) << std::endl;
> std::cout << "record_batch->num_columns(): " <<
> record_batch->num_columns() << std::endl;
> std::cout << "record_batch->num_rows(): " << record_batch->num_rows() <<
> std::endl;
> std::cout << "record_batch->column(0)->length(): "
> << record_batch->column(0)->length() << std::endl;
> std::cout << "record_batch->column(0)->ToString(): "
> << record_batch->column(0)->ToString() << std::endl;
> }
> {code}
> {{record_batch->column(0)->ToString()}} would incur a segmentation fault if
> retrieving Record Batch is wrapped in a function:
> {code:java}
> std::shared_ptr<arrow::RecordBatch> GetRecordBatchFromPlasma(plasma::ObjectID
> object_id)
> {
> // Start up and connect a Plasma client.
> plasma::PlasmaClient client;
> ARROW_CHECK_OK(client.Connect("/tmp/store"));
> plasma::ObjectBuffer object_buffer;
> ARROW_CHECK_OK(client.Get(&object_id, 1, -1, &object_buffer));
> // Retrieve object data.
> auto buffer = object_buffer.data;
> arrow::io::BufferReader buffer_reader(buffer);
> std::shared_ptr<arrow::ipc::RecordBatchReader> record_batch_stream_reader;
> ARROW_CHECK_OK(arrow::ipc::RecordBatchStreamReader::Open(&buffer_reader,
> &record_batch_stream_reader));
> std::shared_ptr<arrow::RecordBatch> record_batch;
> arrow::Status status =
> record_batch_stream_reader->ReadNext(&record_batch);
> // Disconnect the client.
> ARROW_CHECK_OK(client.Disconnect());
> return record_batch;
> }
> int main(int argc, char **argv)
> {
> plasma::ObjectID object_id =
> plasma::ObjectID::from_binary("0FF1CE00C0FFEE00BEEF");
> std::shared_ptr<arrow::RecordBatch> record_batch =
> GetRecordBatchFromPlasma(object_id);
> std::cout << "record_batch->column_name(0): " <<
> record_batch->column_name(0) << std::endl;
> std::cout << "record_batch->num_columns(): " <<
> record_batch->num_columns() << std::endl;
> std::cout << "record_batch->num_rows(): " << record_batch->num_rows() <<
> std::endl;
> std::cout << "record_batch->column(0)->length(): "
> << record_batch->column(0)->length() << std::endl;
> std::cout << "record_batch->column(0)->ToString(): "
> << record_batch->column(0)->ToString() << std::endl;
> }
> {code}
> The meta info of the Record Batch such as number of columns and rows is still
> available, but I can't see the content of the columns.
> {{lldb}} says that the stop reason is {{EXC_BAD_ACCESS}}, so I think the
> Record Batch is destroyed after {{GetRecordBatchFromPlasma}} finishes. But
> why can I still see the meta info of this Record Batch?
> What is the proper way to get the Record Batch if we insist using a function?
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