[jira] [Created] (ARROW-10625) [C++] Optimize Future<> creation

["Ben Kietzman (Jira)" <ji...@apache.org>]

Ben Kietzman created ARROW-10625:
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             Summary: [C++] Optimize Future<> creation
                 Key: ARROW-10625
                 URL: https://issues.apache.org/jira/browse/ARROW-10625
             Project: Apache Arrow
          Issue Type: Improvement
          Components: C++
    Affects Versions: 2.0.0
            Reporter: Ben Kietzman
            Assignee: Ben Kietzman
             Fix For: 3.0.0


{{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



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