prio-queue: factor out compare and swap operations
[git/git.git] / prio-queue.h
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b4b594a3
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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 */
22typedef int (*prio_queue_compare_fn)(const void *one, const void *two, void *cb_data);
23
24struct prio_queue {
25 prio_queue_compare_fn compare;
26 void *cb_data;
27 int alloc, nr;
28 void **array;
29};
30
31/*
32 * Add the "thing" to the queue.
33 */
34extern void prio_queue_put(struct prio_queue *, void *thing);
35
36/*
37 * Extract the "thing" that compares the smallest out of the queue,
38 * or NULL. If compare function is NULL, the queue acts as a LIFO
39 * stack.
40 */
41extern void *prio_queue_get(struct prio_queue *);
42
43extern void clear_prio_queue(struct prio_queue *);
44
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45/* Reverse the LIFO elements */
46extern void prio_queue_reverse(struct prio_queue *);
47
b4b594a3 48#endif /* PRIO_QUEUE_H */