[PATCH v6 13/20] reftable: add a heap-based priority queue for reftable records

["Han-Wen Nienhuys via GitGitGadget" <gitgitgadget@gmail.com>]

From: Han-Wen Nienhuys <hanwen@google.com>

This is needed to create a merged view multiple reftables

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
---
 Makefile                  |   2 +
 reftable/pq.c             | 115 ++++++++++++++++++++++++++++++++++++++
 reftable/pq.h             |  32 +++++++++++
 reftable/pq_test.c        |  72 ++++++++++++++++++++++++
 reftable/reftable-tests.h |   1 +
 t/helper/test-reftable.c  |   1 +
 6 files changed, 223 insertions(+)
 create mode 100644 reftable/pq.c
 create mode 100644 reftable/pq.h
 create mode 100644 reftable/pq_test.c

diff --git a/Makefile b/Makefile
index b23e4a82063a..74560a9605bb 100644
--- a/Makefile
+++ b/Makefile
@@ -2406,6 +2406,7 @@ REFTABLE_OBJS += reftable/block.o
 REFTABLE_OBJS += reftable/blocksource.o
 REFTABLE_OBJS += reftable/iter.o
 REFTABLE_OBJS += reftable/publicbasics.o
+REFTABLE_OBJS += reftable/pq.o
 REFTABLE_OBJS += reftable/reader.o
 REFTABLE_OBJS += reftable/record.o
 REFTABLE_OBJS += reftable/reftable.o
@@ -2415,6 +2416,7 @@ REFTABLE_OBJS += reftable/zlib-compat.o
 
 REFTABLE_TEST_OBJS += reftable/basics_test.o
 REFTABLE_TEST_OBJS += reftable/block_test.o
+REFTABLE_TEST_OBJS += reftable/pq_test.o
 REFTABLE_TEST_OBJS += reftable/record_test.o
 REFTABLE_TEST_OBJS += reftable/reftable_test.o
 REFTABLE_TEST_OBJS += reftable/test_framework.o
diff --git a/reftable/pq.c b/reftable/pq.c
new file mode 100644
index 000000000000..8918d158e2d4
--- /dev/null
+++ b/reftable/pq.c
@@ -0,0 +1,115 @@
+/*
+Copyright 2020 Google LLC
+
+Use of this source code is governed by a BSD-style
+license that can be found in the LICENSE file or at
+https://developers.google.com/open-source/licenses/bsd
+*/
+
+#include "pq.h"
+
+#include "reftable-record.h"
+#include "system.h"
+#include "basics.h"
+
+static int pq_less(struct pq_entry a, struct pq_entry b)
+{
+	struct strbuf ak = STRBUF_INIT;
+	struct strbuf bk = STRBUF_INIT;
+	int cmp = 0;
+	reftable_record_key(&a.rec, &ak);
+	reftable_record_key(&b.rec, &bk);
+
+	cmp = strbuf_cmp(&ak, &bk);
+
+	strbuf_release(&ak);
+	strbuf_release(&bk);
+
+	if (cmp == 0)
+		return a.index > b.index;
+
+	return cmp < 0;
+}
+
+struct pq_entry merged_iter_pqueue_top(struct merged_iter_pqueue pq)
+{
+	return pq.heap[0];
+}
+
+int merged_iter_pqueue_is_empty(struct merged_iter_pqueue pq)
+{
+	return pq.len == 0;
+}
+
+void merged_iter_pqueue_check(struct merged_iter_pqueue pq)
+{
+	int i = 0;
+	for (i = 1; i < pq.len; i++) {
+		int parent = (i - 1) / 2;
+
+		assert(pq_less(pq.heap[parent], pq.heap[i]));
+	}
+}
+
+struct pq_entry merged_iter_pqueue_remove(struct merged_iter_pqueue *pq)
+{
+	int i = 0;
+	struct pq_entry e = pq->heap[0];
+	pq->heap[0] = pq->heap[pq->len - 1];
+	pq->len--;
+
+	i = 0;
+	while (i < pq->len) {
+		int min = i;
+		int j = 2 * i + 1;
+		int k = 2 * i + 2;
+		if (j < pq->len && pq_less(pq->heap[j], pq->heap[i])) {
+			min = j;
+		}
+		if (k < pq->len && pq_less(pq->heap[k], pq->heap[min])) {
+			min = k;
+		}
+
+		if (min == i) {
+			break;
+		}
+
+		SWAP(pq->heap[i], pq->heap[min]);
+		i = min;
+	}
+
+	return e;
+}
+
+void merged_iter_pqueue_add(struct merged_iter_pqueue *pq, struct pq_entry e)
+{
+	int i = 0;
+	if (pq->len == pq->cap) {
+		pq->cap = 2 * pq->cap + 1;
+		pq->heap = reftable_realloc(pq->heap,
+					    pq->cap * sizeof(struct pq_entry));
+	}
+
+	pq->heap[pq->len++] = e;
+	i = pq->len - 1;
+	while (i > 0) {
+		int j = (i - 1) / 2;
+		if (pq_less(pq->heap[j], pq->heap[i])) {
+			break;
+		}
+
+		SWAP(pq->heap[j], pq->heap[i]);
+
+		i = j;
+	}
+}
+
+void merged_iter_pqueue_release(struct merged_iter_pqueue *pq)
+{
+	int i = 0;
+	for (i = 0; i < pq->len; i++) {
+		reftable_record_destroy(&pq->heap[i].rec);
+	}
+	FREE_AND_NULL(pq->heap);
+	pq->len = pq->cap = 0;
+}
diff --git a/reftable/pq.h b/reftable/pq.h
new file mode 100644
index 000000000000..385d2fb139a6
--- /dev/null
+++ b/reftable/pq.h
@@ -0,0 +1,32 @@
+/*
+Copyright 2020 Google LLC
+
+Use of this source code is governed by a BSD-style
+license that can be found in the LICENSE file or at
+https://developers.google.com/open-source/licenses/bsd
+*/
+
+#ifndef PQ_H
+#define PQ_H
+
+#include "record.h"
+
+struct pq_entry {
+	int index;
+	struct reftable_record rec;
+};
+
+struct merged_iter_pqueue {
+	struct pq_entry *heap;
+	size_t len;
+	size_t cap;
+};
+
+struct pq_entry merged_iter_pqueue_top(struct merged_iter_pqueue pq);
+int merged_iter_pqueue_is_empty(struct merged_iter_pqueue pq);
+void merged_iter_pqueue_check(struct merged_iter_pqueue pq);
+struct pq_entry merged_iter_pqueue_remove(struct merged_iter_pqueue *pq);
+void merged_iter_pqueue_add(struct merged_iter_pqueue *pq, struct pq_entry e);
+void merged_iter_pqueue_release(struct merged_iter_pqueue *pq);
+
+#endif
diff --git a/reftable/pq_test.c b/reftable/pq_test.c
new file mode 100644
index 000000000000..5178980b37ed
--- /dev/null
+++ b/reftable/pq_test.c
@@ -0,0 +1,72 @@
+/*
+Copyright 2020 Google LLC
+
+Use of this source code is governed by a BSD-style
+license that can be found in the LICENSE file or at
+https://developers.google.com/open-source/licenses/bsd
+*/
+
+#include "system.h"
+
+#include "basics.h"
+#include "constants.h"
+#include "pq.h"
+#include "record.h"
+#include "reftable-tests.h"
+#include "test_framework.h"
+
+static void test_pq(void)
+{
+	char *names[54] = { NULL };
+	int N = ARRAY_SIZE(names) - 1;
+
+	struct merged_iter_pqueue pq = { NULL };
+	const char *last = NULL;
+
+	int i = 0;
+	for (i = 0; i < N; i++) {
+		char name[100];
+		snprintf(name, sizeof(name), "%02d", i);
+		names[i] = xstrdup(name);
+	}
+
+	i = 1;
+	do {
+		struct reftable_record rec =
+			reftable_new_record(BLOCK_TYPE_REF);
+		struct pq_entry e = { 0 };
+
+		reftable_record_as_ref(&rec)->refname = names[i];
+		e.rec = rec;
+		merged_iter_pqueue_add(&pq, e);
+		merged_iter_pqueue_check(pq);
+		i = (i * 7) % N;
+	} while (i != 1);
+
+	while (!merged_iter_pqueue_is_empty(pq)) {
+		struct pq_entry e = merged_iter_pqueue_remove(&pq);
+		struct reftable_ref_record *ref =
+			reftable_record_as_ref(&e.rec);
+
+		merged_iter_pqueue_check(pq);
+
+		if (last != NULL) {
+			assert(strcmp(last, ref->refname) < 0);
+		}
+		last = ref->refname;
+		ref->refname = NULL;
+		reftable_free(ref);
+	}
+
+	for (i = 0; i < N; i++) {
+		reftable_free(names[i]);
+	}
+
+	merged_iter_pqueue_release(&pq);
+}
+
+int pq_test_main(int argc, const char *argv[])
+{
+	RUN_TEST(test_pq);
+	return 0;
+}
diff --git a/reftable/reftable-tests.h b/reftable/reftable-tests.h
index 5e7698ae654e..495556572e20 100644
--- a/reftable/reftable-tests.h
+++ b/reftable/reftable-tests.h
@@ -12,6 +12,7 @@ license that can be found in the LICENSE file or at
 int basics_test_main(int argc, const char **argv);
 int block_test_main(int argc, const char **argv);
 int merged_test_main(int argc, const char **argv);
+int pq_test_main(int argc, const char **argv);
 int record_test_main(int argc, const char **argv);
 int refname_test_main(int argc, const char **argv);
 int reftable_test_main(int argc, const char **argv);
diff --git a/t/helper/test-reftable.c b/t/helper/test-reftable.c
index fdf925867375..368eb7339eb7 100644
--- a/t/helper/test-reftable.c
+++ b/t/helper/test-reftable.c
@@ -5,6 +5,7 @@ int cmd__reftable(int argc, const char **argv)
 {
 	basics_test_main(argc, argv);
 	block_test_main(argc, argv);
+	pq_test_main(argc, argv);
 	record_test_main(argc, argv);
 	reftable_test_main(argc, argv);
 	tree_test_main(argc, argv);
-- 
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