Merge branch 'mh/notes-duplicate-entries'
[git/git.git] / prio-queue.h
1 #ifndef PRIO_QUEUE_H
2 #define PRIO_QUEUE_H
3
4 /*
5 * A priority queue implementation, primarily for keeping track of
6 * commits in the 'date-order' so that we process them from new to old
7 * as they are discovered, but can be used to hold any pointer to
8 * struct. The caller is responsible for supplying a function to
9 * compare two "things".
10 *
11 * Alternatively, this data structure can also be used as a LIFO stack
12 * by specifying NULL as the comparison function.
13 */
14
15 /*
16 * Compare two "things", one and two; the third parameter is cb_data
17 * in the prio_queue structure. The result is returned as a sign of
18 * the return value, being the same as the sign of the result of
19 * subtracting "two" from "one" (i.e. negative if "one" sorts earlier
20 * than "two").
21 */
22 typedef int (*prio_queue_compare_fn)(const void *one, const void *two, void *cb_data);
23
24 struct prio_queue_entry {
25 unsigned ctr;
26 void *data;
27 };
28
29 struct prio_queue {
30 prio_queue_compare_fn compare;
31 unsigned insertion_ctr;
32 void *cb_data;
33 int alloc, nr;
34 struct prio_queue_entry *array;
35 };
36
37 /*
38 * Add the "thing" to the queue.
39 */
40 void prio_queue_put(struct prio_queue *, void *thing);
41
42 /*
43 * Extract the "thing" that compares the smallest out of the queue,
44 * or NULL. If compare function is NULL, the queue acts as a LIFO
45 * stack.
46 */
47 void *prio_queue_get(struct prio_queue *);
48
49 /*
50 * Gain access to the "thing" that would be returned by
51 * prio_queue_get, but do not remove it from the queue.
52 */
53 void *prio_queue_peek(struct prio_queue *);
54
55 void clear_prio_queue(struct prio_queue *);
56
57 /* Reverse the LIFO elements */
58 void prio_queue_reverse(struct prio_queue *);
59
60 #endif /* PRIO_QUEUE_H */