lttng lib: lttng priority heap

/*

 * lttng_prio_heap.c

 *

 * Priority heap containing pointers. Based on CLRS, chapter 6.

 *

 * Copyright 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

 *

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 */

#include <linux/slab.h>

#include "lttng_prio_heap.h"

#ifdef DEBUG_HEAP

void lttng_check_heap(const struct lttng_ptr_heap *heap)

{

	size_t i;

	if (!heap->len)

		return;

	for (i = 1; i < heap->len; i++)

		WARN_ON_ONCE(!heap->gt(heap->ptrs[i], heap->ptrs[0]));

}

#endif

static

size_t parent(size_t i)

{

	return (i -1) >> 1;

}

static

size_t left(size_t i)

{

	return (i << 1) + 1;

}

static

size_t right(size_t i)

{

	return (i << 1) + 2;

}

/*

 * Copy of heap->ptrs pointer is invalid after heap_grow.

 */

static

int heap_grow(struct lttng_ptr_heap *heap, size_t new_len)

{

	void **new_ptrs;

	if (heap->alloc_len >= new_len)

		return 0;

	heap->alloc_len = max_t(size_t, new_len, heap->alloc_len << 1);

	new_ptrs = kmalloc(heap->alloc_len * sizeof(void *), heap->gfpmask);

	if (!new_ptrs)

		return -ENOMEM;

	if (heap->ptrs)

		memcpy(new_ptrs, heap->ptrs, heap->len * sizeof(void *));

	kfree(heap->ptrs);

	heap->ptrs = new_ptrs;

	return 0;

}

static

int heap_set_len(struct lttng_ptr_heap *heap, size_t new_len)

{

	int ret;

	ret = heap_grow(heap, new_len);

	if (ret)

		return ret;

	heap->len = new_len;

	return 0;

}

int lttng_heap_init(struct lttng_ptr_heap *heap, size_t alloc_len,

	      gfp_t gfpmask, int gt(void *a, void *b))

{

	heap->ptrs = NULL;

	heap->len = 0;

	heap->alloc_len = 0;

	heap->gt = gt;

	heap->gfpmask = gfpmask;

	/*

	 * Minimum size allocated is 1 entry to ensure memory allocation

	 * never fails within heap_replace_max.

	 */

	return heap_grow(heap, max_t(size_t, 1, alloc_len));

}

void lttng_heap_free(struct lttng_ptr_heap *heap)

{

	kfree(heap->ptrs);

}

static void heapify(struct lttng_ptr_heap *heap, size_t i)

{

	void **ptrs = heap->ptrs;

	size_t l, r, largest;

	for (;;) {

		void *tmp;

		l = left(i);

		r = right(i);

		if (l < heap->len && heap->gt(ptrs[l], ptrs[i]))

			largest = l;

		else

			largest = i;

		if (r < heap->len && heap->gt(ptrs[r], ptrs[largest]))

			largest = r;

		if (largest == i)

			break;

		tmp = ptrs[i];

		ptrs[i] = ptrs[largest];

		ptrs[largest] = tmp;

		i = largest;

	}

	lttng_check_heap(heap);

}

void *lttng_heap_replace_max(struct lttng_ptr_heap *heap, void *p)

{

	void *res;

	if (!heap->len) {

		(void) heap_set_len(heap, 1);

		heap->ptrs[0] = p;

		lttng_check_heap(heap);

		return NULL;

	}

	/* Replace the current max and heapify */

	res = heap->ptrs[0];

	heap->ptrs[0] = p;

	heapify(heap, 0);

	return res;

}

int lttng_heap_insert(struct lttng_ptr_heap *heap, void *p)

{

	void **ptrs;

	size_t pos;

	int ret;

	ret = heap_set_len(heap, heap->len + 1);

	if (ret)

		return ret;

	ptrs = heap->ptrs;

	pos = heap->len - 1;

	while (pos > 0 && heap->gt(p, ptrs[parent(pos)])) {

		/* Move parent down until we find the right spot */

		ptrs[pos] = ptrs[parent(pos)];

		pos = parent(pos);

	}

	ptrs[pos] = p;

	lttng_check_heap(heap);

	return 0;

}

void *lttng_heap_remove(struct lttng_ptr_heap *heap)

{

	switch (heap->len) {

	case 0:

		return NULL;

	case 1:

		(void) heap_set_len(heap, 0);

		return heap->ptrs[0];

	}

	/* Shrink, replace the current max by previous last entry and heapify */

	heap_set_len(heap, heap->len - 1);

	/* len changed. previous last entry is at heap->len */

	return lttng_heap_replace_max(heap, heap->ptrs[heap->len]);

}

void *lttng_heap_cherrypick(struct lttng_ptr_heap *heap, void *p)

{

	size_t pos, len = heap->len;

	for (pos = 0; pos < len; pos++)

		if (heap->ptrs[pos] == p)

			goto found;

	return NULL;

found:

	if (heap->len == 1) {

		(void) heap_set_len(heap, 0);

		lttng_check_heap(heap);

		return heap->ptrs[0];

	}

	/* Replace p with previous last entry and heapify. */

	heap_set_len(heap, heap->len - 1);

	/* len changed. previous last entry is at heap->len */

	heap->ptrs[pos] = heap->ptrs[heap->len];

	heapify(heap, pos);

	return p;

}

#ifndef _LTTNG_PRIO_HEAP_H

#define _LTTNG_PRIO_HEAP_H

/*

 * lttng_prio_heap.h

 *

 * Priority heap containing pointers. Based on CLRS, chapter 6.

 *

 * Copyright 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

 *

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to deal

 * in the Software without restriction, including without limitation the rights

 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

 * copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 */

#include <linux/gfp.h>

struct lttng_ptr_heap {

	size_t len, alloc_len;

	void **ptrs;

	int (*gt)(void *a, void *b);

	gfp_t gfpmask;

};

#ifdef DEBUG_HEAP

void lttng_check_heap(const struct lttng_ptr_heap *heap);

#else

static inline

void lttng_check_heap(const struct lttng_ptr_heap *heap)

{

}

#endif

/**

 * lttng_heap_maximum - return the largest element in the heap

 * @heap: the heap to be operated on

 *

 * Returns the largest element in the heap, without performing any modification

 * to the heap structure. Returns NULL if the heap is empty.

 */

static inline void *lttng_heap_maximum(const struct lttng_ptr_heap *heap)

{

	lttng_check_heap(heap);

	return heap->len ? heap->ptrs[0] : NULL;

}

/**

 * lttng_heap_init - initialize the heap

 * @heap: the heap to initialize

 * @alloc_len: number of elements initially allocated

 * @gfp: allocation flags

 * @gt: function to compare the elements

 *

 * Returns -ENOMEM if out of memory.

 */

extern int lttng_heap_init(struct lttng_ptr_heap *heap,

		     size_t alloc_len, gfp_t gfpmask,

		     int gt(void *a, void *b));

/**

 * lttng_heap_free - free the heap

 * @heap: the heap to free

 */

extern void lttng_heap_free(struct lttng_ptr_heap *heap);

/**

 * lttng_heap_insert - insert an element into the heap

 * @heap: the heap to be operated on

 * @p: the element to add

 *

 * Insert an element into the heap.

 *

 * Returns -ENOMEM if out of memory.

 */

extern int lttng_heap_insert(struct lttng_ptr_heap *heap, void *p);

/**

 * lttng_heap_remove - remove the largest element from the heap

 * @heap: the heap to be operated on

 *

 * Returns the largest element in the heap. It removes this element from the

 * heap. Returns NULL if the heap is empty.

 */

extern void *lttng_heap_remove(struct lttng_ptr_heap *heap);

/**

 * lttng_heap_cherrypick - remove a given element from the heap

 * @heap: the heap to be operated on

 * @p: the element

 *

 * Remove the given element from the heap. Return the element if present, else

 * return NULL. This algorithm has a complexity of O(n), which is higher than

 * O(log(n)) provided by the rest of this API.

 */

extern void *lttng_heap_cherrypick(struct lttng_ptr_heap *heap, void *p);

/**

 * lttng_heap_replace_max - replace the the largest element from the heap

 * @heap: the heap to be operated on

 * @p: the pointer to be inserted as topmost element replacement

 *

 * Returns the largest element in the heap. It removes this element from the

 * heap. The heap is rebalanced only once after the insertion. Returns NULL if

 * the heap is empty.

 *

 * This is the equivalent of calling heap_remove() and then heap_insert(), but

 * it only rebalances the heap once. It never allocates memory.

 */

extern void *lttng_heap_replace_max(struct lttng_ptr_heap *heap, void *p);

#endif /* _LTTNG_PRIO_HEAP_H */