ywc88 commented on issue #958:
URL: https://github.com/apache/arrow-adbc/issues/958#issuecomment-1665987486
I'm still getting familiar with the codebase particularly on the PostgreSQL
side, but it looks like what's happening is that the segfault is happening in
`GetSchema` where `copy_reader_` isn't initialized correctly before getting
dereferenced with `copy_reader_->GetSchema(out);`, see below:
```cpp
int TupleReader::GetSchema(struct ArrowSchema* out) {
int na_res = copy_reader_->GetSchema(out);
if (out->release == nullptr) {
StringBuilderAppend(&error_builder_,
"[libpq] Result set was already consumed or freed");
return EINVAL;
} else if (na_res != NANOARROW_OK) {
// e.g., Can't allocate memory
StringBuilderAppend(&error_builder_, "[libpq] Error copying schema");
}
return na_res;
}
```
The segfault doesn't happen when switching to pyarrow 11, and the difference
between 10 and 11 is that `CacheSchema()` is removed, where I think
`stream_.get_schema(&stream_, &c_schema)` calls `TupleReader::GetSchema` before
`copy_reader_` is initialized correctly (@lidavidm maybe this is the bug you
were referencing earlier?).
For reference, below is `ArrayStreamBatchReader` from `maint-10.0.1`:
```cpp
class ArrayStreamBatchReader : public RecordBatchReader {
public:
explicit ArrayStreamBatchReader(struct ArrowArrayStream* stream) {
ArrowArrayStreamMove(stream, &stream_);
DCHECK(!ArrowArrayStreamIsReleased(&stream_));
}
~ArrayStreamBatchReader() {
if (!ArrowArrayStreamIsReleased(&stream_)) {
ArrowArrayStreamRelease(&stream_);
}
DCHECK(ArrowArrayStreamIsReleased(&stream_));
}
std::shared_ptr<Schema> schema() const override { return CacheSchema(); }
Status ReadNext(std::shared_ptr<RecordBatch>* batch) override {
struct ArrowArray c_array;
RETURN_NOT_OK(StatusFromCError(stream_.get_next(&stream_, &c_array)));
if (ArrowArrayIsReleased(&c_array)) {
// End of stream
batch->reset();
return Status::OK();
} else {
return ImportRecordBatch(&c_array, CacheSchema()).Value(batch);
}
}
Status Close() override {
if (!ArrowArrayStreamIsReleased(&stream_)) {
ArrowArrayStreamRelease(&stream_);
}
return Status::OK();
}
private:
std::shared_ptr<Schema> CacheSchema() const {
if (!schema_) {
struct ArrowSchema c_schema;
ARROW_CHECK_OK(StatusFromCError(stream_.get_schema(&stream_,
&c_schema)));
schema_ = ImportSchema(&c_schema).ValueOrDie();
}
return schema_;
}
...
```
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