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When consuming a priority queue, it can be convenient to inspect the next object that will be dequeued without actually dequeueing it. Our existing library did not have such a 'peek' operation, so add it as prio_queue_peek(). Add a reference-level comparison in t/helper/test-prio-queue.c so this method is exercised by t0009-prio-queue.sh. Further, add a test that checks the behavior when the compare function is NULL (i.e. the queue becomes a stack). Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
60 lines
1.7 KiB
C
60 lines
1.7 KiB
C
#ifndef PRIO_QUEUE_H
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#define PRIO_QUEUE_H
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/*
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* A priority queue implementation, primarily for keeping track of
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* commits in the 'date-order' so that we process them from new to old
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* as they are discovered, but can be used to hold any pointer to
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* struct. The caller is responsible for supplying a function to
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* compare two "things".
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*
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* Alternatively, this data structure can also be used as a LIFO stack
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* by specifying NULL as the comparison function.
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*/
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/*
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* Compare two "things", one and two; the third parameter is cb_data
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* in the prio_queue structure. The result is returned as a sign of
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* the return value, being the same as the sign of the result of
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* subtracting "two" from "one" (i.e. negative if "one" sorts earlier
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* than "two").
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*/
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typedef int (*prio_queue_compare_fn)(const void *one, const void *two, void *cb_data);
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struct prio_queue_entry {
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unsigned ctr;
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void *data;
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};
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struct prio_queue {
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prio_queue_compare_fn compare;
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unsigned insertion_ctr;
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void *cb_data;
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int alloc, nr;
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struct prio_queue_entry *array;
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};
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/*
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* Add the "thing" to the queue.
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*/
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extern void prio_queue_put(struct prio_queue *, void *thing);
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/*
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* Extract the "thing" that compares the smallest out of the queue,
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* or NULL. If compare function is NULL, the queue acts as a LIFO
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* stack.
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*/
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extern void *prio_queue_get(struct prio_queue *);
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/*
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* Gain access to the "thing" that would be returned by
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* prio_queue_get, but do not remove it from the queue.
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*/
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extern void *prio_queue_peek(struct prio_queue *);
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extern void clear_prio_queue(struct prio_queue *);
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/* Reverse the LIFO elements */
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extern void prio_queue_reverse(struct prio_queue *);
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#endif /* PRIO_QUEUE_H */
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