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Defer the actual removal in prio_queue_get() until the next
operation. If that next operation is a prio_queue_put(), the
removal and insertion are fused into a single replace — writing
the new element at the root and sifting it down — which avoids
a full remove-rebalance-insert cycle.
This matches the dominant usage pattern in git's commit traversal:
get a commit, then put its parents. The first parent insertion
after each get is now a replace operation automatically.
This generalizes the lazy_queue pattern from builtin/describe.c
(introduced in 08bb69d70f) into prio_queue itself. Three callers
independently implemented the same get+put fusion:
- builtin/describe.c had a full lazy_queue wrapper
- commit.c:pop_most_recent_commit() used peek+replace
- builtin/show-branch.c:join_revs() used peek+replace
All three now collapse to plain _get() and _put(), with the data
structure handling the fusion internally. This simplifies callers
and means every prio_queue user gets the optimization for free
without needing to implement it manually.
Remove prio_queue_replace() since no external callers remain.
Benchmarked on a 1.8M-commit monorepo (30 interleaved runs,
paired t-test, Xeon @ 2.20GHz):
Code paths that previously did eager get+put (new optimization):
Command base patched change p
merge-base --all A A~1000 3828ms 3725ms -2.69% 0.0001
rev-list --count A~1000..A 3055ms 2986ms -2.27% 0.0601
log --oneline A~1000..A 3408ms 3350ms -1.71% 0.0482
Code paths that already had manual get+put fusion (expect
neutral — the optimization moves into prio_queue but the number
of heap operations stays the same):
Command base patched change p
show-branch A A~1000 9156ms 9127ms -0.32% 0.3470
describe (4751 revs, 81K repo) 1983ms 1963ms -1.02% <0.001
No regressions in any scenario.
Suggested-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Kristofer Karlsson <krka@spotify.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Add a function to replace the top element of the queue that basically
does the same as prio_queue_get() followed by prio_queue_put(), but
without the work by prio_queue_get() to rebalance the heap. It can be
used to optimize loops that get one element and then immediately add
another one. That's common e.g., with commit history traversal, where
we get out a commit and then put in its parents.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Convert the prio-queue test script to clar framework by using clar
assertions where necessary. Test functions are created as a standalone
to test different cases.
update the type of the variable `j` from int to `size_t`, this ensures
compatibility with the type used for result_size, which is also size_t,
preventing a potential warning or error caused by comparisons between
signed and unsigned integers.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Seyi Kuforiji <kuforiji98@gmail.com>
Acked-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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