[ARROW-11488] [Rust]: StructBuilder's Drop impl leaks memory

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.0
• Fix Version/s: 3.0.1, 4.0.0
• Component/s: Rust
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/27369
• Assignee: Steven Fackler
• Reporter: Steven Fackler
• Created: 03/Feb/21 21:31
• Updated: 11/Jan/23 08:20
• Resolved: 04/Feb/21 17:45

Description

The StructBuilder stores two copies of the inner ArrayBuilders in two separate Vecs via some unsafe code. To avoid double-dropping the builders, the StructBuilder Drop impl uses mem::forget on one of the vectors. This avoids calling the destructor of the ArrayBuilders twice, but also leaks the memory of the Vec itself.

In addition, the double-vecs with the unsafe code is completely unnecessary since you can just call `ArrayBuilder::as_mut_any` on the `dyn ArrayBuilder` instead of having to covert to a `Box<dyn Any>`.

Issue Links

• links to: GitHub Pull Request #9409