include/lttng/prio_heap.h

   1 /* SPDX-License-Identifier: MIT
   2  *
   3  * lttng/prio_heap.h
   4  *
   5  * Priority heap containing pointers. Based on CLRS, chapter 6.
   6  *
   7  * Copyright 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  */
   9
  10 #ifndef _LTTNG_PRIO_HEAP_H
  11 #define _LTTNG_PRIO_HEAP_H
  12
  13 #include <linux/gfp.h>
  14
  15 struct lttng_ptr_heap {
  16         size_t len, alloc_len;
  17         void **ptrs;
  18         int (*gt)(void *a, void *b);
  19         gfp_t gfpmask;
  20 };
  21
  22 #ifdef DEBUG_HEAP
  23 void lttng_check_heap(const struct lttng_ptr_heap *heap);
  24 #else
  25 static inline
  26 void lttng_check_heap(const struct lttng_ptr_heap *heap)
  27 {
  28 }
  29 #endif
  30
  31 /**
  32  * lttng_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 *lttng_heap_maximum(const struct lttng_ptr_heap *heap)
  39 {
  40         lttng_check_heap(heap);
  41         return heap->len ? heap->ptrs[0] : NULL;
  42 }
  43
  44 /**
  45  * lttng_heap_init - initialize the heap
  46  * @heap: the heap to initialize
  47  * @alloc_len: number of elements initially allocated
  48  * @gfp: allocation flags
  49  * @gt: function to compare the elements
  50  *
  51  * Returns -ENOMEM if out of memory.
  52  */
  53 extern int lttng_heap_init(struct lttng_ptr_heap *heap,
  54                      size_t alloc_len, gfp_t gfpmask,
  55                      int gt(void *a, void *b));
  56
  57 /**
  58  * lttng_heap_free - free the heap
  59  * @heap: the heap to free
  60  */
  61 extern void lttng_heap_free(struct lttng_ptr_heap *heap);
  62
  63 /**
  64  * lttng_heap_insert - insert an element into the heap
  65  * @heap: the heap to be operated on
  66  * @p: the element to add
  67  *
  68  * Insert an element into the heap.
  69  *
  70  * Returns -ENOMEM if out of memory.
  71  */
  72 extern int lttng_heap_insert(struct lttng_ptr_heap *heap, void *p);
  73
  74 /**
  75  * lttng_heap_remove - remove the largest element from the heap
  76  * @heap: the heap to be operated on
  77  *
  78  * Returns the largest element in the heap. It removes this element from the
  79  * heap. Returns NULL if the heap is empty.
  80  */
  81 extern void *lttng_heap_remove(struct lttng_ptr_heap *heap);
  82
  83 /**
  84  * lttng_heap_cherrypick - remove a given element from the heap
  85  * @heap: the heap to be operated on
  86  * @p: the element
  87  *
  88  * Remove the given element from the heap. Return the element if present, else
  89  * return NULL. This algorithm has a complexity of O(n), which is higher than
  90  * O(log(n)) provided by the rest of this API.
  91  */
  92 extern void *lttng_heap_cherrypick(struct lttng_ptr_heap *heap, void *p);
  93
  94 /**
  95  * lttng_heap_replace_max - replace the the largest element from the heap
  96  * @heap: the heap to be operated on
  97  * @p: the pointer to be inserted as topmost element replacement
  98  *
  99  * Returns the largest element in the heap. It removes this element from the
 100  * heap. The heap is rebalanced only once after the insertion. Returns NULL if
 101  * the heap is empty.
 102  *
 103  * This is the equivalent of calling heap_remove() and then heap_insert(), but
 104  * it only rebalances the heap once. It never allocates memory.
 105  */
 106 extern void *lttng_heap_replace_max(struct lttng_ptr_heap *heap, void *p);
 107
 108 #endif /* _LTTNG_PRIO_HEAP_H */