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https://issues.apache.org/jira/browse/ARROW-7522?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17012031#comment-17012031
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Wes McKinney commented on ARROW-7522:
-------------------------------------
Seems like that any Plasma memory accessed by the client is invalidated as soon
as the client is disconnected or destroyed. If you keep the PlasmaClient alive
I'm guessing it will not happen.
[~robertnishihara] or [~pcmoritz] may be able to comment on whether this is by
design or something that could be fixed potentially. It seems like keeping the
mmaps alive could be doable
> [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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