Optimize the sequence get+put to peek+replace to avoid one unnecessary
heap rebalance.
Do that by tracking partial get operations in a prio_queue wrapper,
struct lazy_queue, and using wrapper functions that turn get into peek
and put into replace as needed. This is simpler than tracking the
state explicitly in the calling code.
We get a nice speedup on top of the previous patch's conversion to
prio_queue:
Benchmark 1: ./git_2.50.1 describe $(git rev-list v2.41.0..v2.47.0)
Time (mean ± σ): 1.559 s ± 0.002 s [User: 1.493 s, System: 0.051 s]
Range (min … max): 1.556 s … 1.563 s 10 runs
Benchmark 2: ./git_describe_pq describe $(git rev-list v2.41.0..v2.47.0)
Time (mean ± σ): 1.204 s ± 0.001 s [User: 1.138 s, System: 0.051 s]
Range (min … max): 1.202 s … 1.205 s 10 runs
Benchmark 3: ./git describe $(git rev-list v2.41.0..v2.47.0)
Time (mean ± σ): 850.9 ms ± 1.6 ms [User: 786.6 ms, System: 49.8 ms]
Range (min … max): 849.1 ms … 854.1 ms 10 runs
Summary
./git describe $(git rev-list v2.41.0..v2.47.0) ran
1.41 ± 0.00 times faster than ./git_describe_pq describe $(git rev-list v2.41.0..v2.47.0)
1.83 ± 0.00 times faster than ./git_2.50.1 describe $(git rev-list v2.41.0..v2.47.0)
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
08bb69d70f