lib/prio_heap/prio_heap.h

   1 #ifndef _LTTNG_PRIO_HEAP_H
   2 #define _LTTNG_PRIO_HEAP_H
   3
   4 /*
   5  * prio_heap.h
   6  *
   7  * Static-sized priority heap containing pointers. Based on CLRS,
   8  * chapter 6.
   9  *
  10  * Copyright 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  11  *
  12  * Permission is hereby granted, free of charge, to any person obtaining a copy
  13  * of this software and associated documentation files (the "Software"), to deal
  14  * in the Software without restriction, including without limitation the rights
  15  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  16  * copies of the Software, and to permit persons to whom the Software is
  17  * furnished to do so, subject to the following conditions:
  18  *
  19  * The above copyright notice and this permission notice shall be included in
  20  * all copies or substantial portions of the Software.
  21  */
  22
  23 #include <linux/gfp.h>
  24
  25 struct ptr_heap {
  26         size_t size, max;
  27         void **ptrs;
  28         int (*gt)(void *a, void *b);
  29 };
  30
  31 /**
  32  * heap_maximum - return the largest element in the heap
  33  * @heap: the heap to be operated on
  34  *
  35  * Returns the largest element in the heap, without performing any modification
  36  * to the heap structure. Returns NULL if the heap is empty.
  37  */
  38 static inline void *heap_maximum(const struct ptr_heap *heap)
  39 {
  40         return heap->size ? heap->ptrs[0] : NULL;
  41 }
  42
  43 /**
  44  * heap_init - initialize the heap
  45  * @heap: the heap to initialize
  46  * @size: maximum number of elements
  47  * @gfp: allocation flags
  48  * @gt: function to compare the elements
  49  *
  50  * Returns -ENOMEM if out of memory.
  51  */
  52 extern int heap_init(struct ptr_heap *heap, size_t size,
  53                      gfp_t gfpmask, int gt(void *a, void *b));
  54
  55 /**
  56  * heap_free - free the heap
  57  * @heap: the heap to free
  58  */
  59 extern void heap_free(struct ptr_heap *heap);
  60
  61 /**
  62  * heap_insert - insert an element into the heap
  63  * @heap: the heap to be operated on
  64  *
  65  * Insert an element into the heap. If the heap is full, return the
  66  * largest element between those previously present in the heap and the
  67  * element being added, else return NULL.
  68  */
  69 extern void *heap_insert(struct ptr_heap *heap, void *p);
  70
  71 /**
  72  * heap_remove - remove the largest element from the heap
  73  * @heap: the heap to be operated on
  74  *
  75  * Returns the largest element in the heap. It removes this element from the
  76  * heap. Returns NULL if the heap is empty.
  77  */
  78 extern void *heap_remove(struct ptr_heap *heap);
  79
  80 /**
  81  * heap_cherrypick - remove a given element from the heap
  82  * @heap: the heap to be operated on
  83  * @p: the element
  84  *
  85  * Remove the given element from the heap. Return the element if present, else
  86  * return NULL. This algorithm has a complexity of O(n), which is higher than
  87  * O(log(n)) provided by the rest of this API.
  88  */
  89 extern void *heap_cherrypick(struct ptr_heap *heap, void *p);
  90
  91 /**
  92  * heap_replace_max - replace the the largest element from the heap
  93  * @heap: the heap to be operated on
  94  * @p: the pointer to be inserted as topmost element replacement
  95  *
  96  * Returns the largest element in the heap. It removes this element from the
  97  * heap. The heap is rebalanced only once after the insertion. Returns NULL if
  98  * the heap is empty.
  99  *
 100  * This is the equivalent of calling heap_remove() and then heap_insert(), but
 101  * it only rebalances the heap once.
 102  */
 103 extern void *heap_replace_max(struct ptr_heap *heap, void *p);
 104
 105 #endif /* _LTTNG_PRIO_HEAP_H */