[ARROW-10625] [C++] Optimize Future<> creation

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.0.0
• Component/s: C++
• Labels: async-util
• External issue URL: https://github.com/apache/arrow/issues/26581
• Assignee: Unassigned
• Reporter: Ben Kietzman
• Created: 16/Nov/20 21:14
• Updated: 11/Jan/23 08:14

Description

Future<> is more expensive to construct than necessary. A few optimizations could be pursued:

• Store the future's result in the same allocation which houses the ConcreteFutureImpl
• Apply the small buffer optimization to FnOnce so that small continuations do not incur another heap allocation
• Contention for the global waiter lock is unlikely to be an issue, but it'd be good to measure
• Futures will usually have few callbacks, so a vector may be unnecessary