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9f75e7a150
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>
118 lines
2.6 KiB
C
118 lines
2.6 KiB
C
#include "unit-test.h"
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#include "prio-queue.h"
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static int intcmp(const void *va, const void *vb, void *data UNUSED)
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{
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const int *a = va, *b = vb;
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return *a - *b;
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}
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#define MISSING -1
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#define DUMP -2
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#define STACK -3
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#define GET -4
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#define REVERSE -5
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#define REPLACE -6
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static int show(int *v)
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{
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return v ? *v : MISSING;
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}
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static void test_prio_queue(int *input, size_t input_size,
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int *result, size_t result_size)
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{
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struct prio_queue pq = { intcmp };
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size_t j = 0;
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for (size_t i = 0; i < input_size; i++) {
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void *peek, *get;
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switch(input[i]) {
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case GET:
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peek = prio_queue_peek(&pq);
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get = prio_queue_get(&pq);
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cl_assert(peek == get);
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cl_assert(j < result_size);
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cl_assert_equal_i(result[j], show(get));
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j++;
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break;
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case DUMP:
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while ((peek = prio_queue_peek(&pq))) {
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get = prio_queue_get(&pq);
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cl_assert(peek == get);
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cl_assert(j < result_size);
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cl_assert_equal_i(result[j], show(get));
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j++;
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}
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break;
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case STACK:
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pq.compare = NULL;
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break;
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case REVERSE:
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prio_queue_reverse(&pq);
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break;
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case REPLACE:
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get = prio_queue_get(&pq);
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cl_assert(i + 1 < input_size);
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cl_assert(input[i + 1] >= 0);
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cl_assert(j < result_size);
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cl_assert_equal_i(result[j], show(get));
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j++;
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prio_queue_put(&pq, &input[++i]);
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break;
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default:
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prio_queue_put(&pq, &input[i]);
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break;
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}
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}
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cl_assert_equal_i(j, result_size);
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clear_prio_queue(&pq);
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}
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#define TEST_INPUT(input, result) \
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test_prio_queue(input, ARRAY_SIZE(input), result, ARRAY_SIZE(result))
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void test_prio_queue__basic(void)
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{
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TEST_INPUT(((int []){ 2, 6, 3, 10, 9, 5, 7, 4, 5, 8, 1, DUMP }),
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((int []){ 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 10 }));
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}
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void test_prio_queue__mixed(void)
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{
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TEST_INPUT(((int []){ 6, 2, 4, GET, 5, 3, GET, GET, 1, DUMP }),
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((int []){ 2, 3, 4, 1, 5, 6 }));
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}
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void test_prio_queue__empty(void)
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{
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TEST_INPUT(((int []){ 1, 2, GET, GET, GET, 1, 2, GET, GET, GET }),
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((int []){ 1, 2, MISSING, 1, 2, MISSING }));
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}
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void test_prio_queue__replace(void)
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{
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TEST_INPUT(((int []){ REPLACE, 6, 2, 4, REPLACE, 5, 7, GET,
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REPLACE, 1, DUMP }),
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((int []){ MISSING, 2, 4, 5, 1, 6, 7 }));
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}
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void test_prio_queue__stack(void)
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{
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TEST_INPUT(((int []){ STACK, 8, 1, 5, 4, 6, 2, 3, DUMP }),
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((int []){ 3, 2, 6, 4, 5, 1, 8 }));
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}
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void test_prio_queue__reverse_stack(void)
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{
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TEST_INPUT(((int []){ STACK, 1, 2, 3, 4, 5, 6, REVERSE, DUMP }),
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((int []){ 1, 2, 3, 4, 5, 6 }));
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}
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void test_prio_queue__replace_stack(void)
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{
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TEST_INPUT(((int []){ STACK, 8, 1, 5, REPLACE, 4, 6, 2, 3, DUMP }),
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((int []){ 5, 3, 2, 6, 4, 1, 8 }));
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}
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