Add heap debug option, fix heap

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/include/babeltrace/prio_heap.h b/include/babeltrace/prio_heap.h
index 51cdac56c26d693a9a655f2318c8b81d3e2c67b8..1a523313f84134d07f75f3c547a294dd6128c0a7 100644 (file)
--- a/include/babeltrace/prio_heap.h
+++ b/include/babeltrace/prio_heap.h
@@ -28,6 +28,15 @@ struct ptr_heap {
        int (*gt)(void *a, void *b);
 };
 
+#ifdef DEBUG_HEAP
+void check_heap(const struct ptr_heap *heap);
+#else
+static inline
+void check_heap(const struct ptr_heap *heap)
+{
+}
+#endif
+
 /**
  * heap_maximum - return the largest element in the heap
  * @heap: the heap to be operated on
@@ -37,6 +46,7 @@ struct ptr_heap {
  */
 static inline void *heap_maximum(const struct ptr_heap *heap)
 {
+       check_heap(heap);
        return heap->len ? heap->ptrs[0] : NULL;
 }
 

diff --git a/lib/prio_heap.c b/lib/prio_heap.c
index f7f351e2a5d799dfabca90700ed66d6faaab2d64..008c4cc3eaa3680b37c5aae97c18f0fd970081c4 100644 (file)
--- a/lib/prio_heap.c
+++ b/lib/prio_heap.c
@@ -21,28 +21,42 @@
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>
+#include <assert.h>
 
 #ifndef max_t
 #define max_t(type, a, b)      \
        ((type) (a) > (type) (b) ? (type) (a) : (type) (b))
 #endif
 
+#ifdef DEBUG_HEAP
+void check_heap(const struct ptr_heap *heap)
+{
+       size_t i;
+
+       if (!heap->len)
+               return;
+
+       for (i = 1; i < heap->len; i++)
+               assert(!heap->gt(heap->ptrs[i], heap->ptrs[0]));
+}
+#endif
+
 static
 size_t parent(size_t i)
 {
-       return i >> 1;
+       return (i - 1) >> 1;
 }
 
 static
 size_t left(size_t i)
 {
-       return i << 1;
+       return (i << 1) + 1;
 }
 
 static
 size_t right(size_t i)
 {
-       return (i << 1) + 1;
+       return (i << 1) + 2;
 }
 
 /*
@@ -104,26 +118,24 @@ static void heapify(struct ptr_heap *heap, size_t i)
        size_t l, r, largest;
 
        for (;;) {
+               void *tmp;
+
                l = left(i);
                r = right(i);
-               if (l <= heap->len && ptrs[l] > ptrs[i])
+               if (l < heap->len && heap->gt(ptrs[l], ptrs[i]))
                        largest = l;
                else
                        largest = i;
-               if (r <= heap->len && ptrs[r] > ptrs[largest])
+               if (r < heap->len && heap->gt(ptrs[r], ptrs[largest]))
                        largest = r;
-               if (largest != i) {
-                       void *tmp;
-
-                       tmp = ptrs[i];
-                       ptrs[i] = ptrs[largest];
-                       ptrs[largest] = tmp;
-                       i = largest;
-                       continue;
-               } else {
+               if (largest == i)
                        break;
-               }
+               tmp = ptrs[i];
+               ptrs[i] = ptrs[largest];
+               ptrs[largest] = tmp;
+               i = largest;
        }
+       check_heap(heap);
 }
 
 void *heap_replace_max(struct ptr_heap *heap, void *p)
@@ -133,6 +145,7 @@ void *heap_replace_max(struct ptr_heap *heap, void *p)
        if (!heap->len) {
                (void) heap_set_len(heap, 1);
                heap->ptrs[0] = p;
+               check_heap(heap);
                return NULL;
        }
 
@@ -153,28 +166,14 @@ int heap_insert(struct ptr_heap *heap, void *p)
        if (ret)
                return ret;
        ptrs = heap->ptrs;
-       /* Add the element to the end */
-       ptrs[heap->len - 1] = p;
        pos = heap->len - 1;
-       /* Bubble it up to the appropriate position. */
-       for (;;) {
-               if (pos > 0 && heap->gt(ptrs[pos], ptrs[parent(pos)])) {
-                       void *tmp;
-
-                       /* Need to exchange */
-                       tmp = ptrs[pos];
-                       ptrs[pos] = ptrs[parent(pos)];
-                       ptrs[parent(pos)] = tmp;
-                       pos = parent(pos);
-                       /*
-                        * No need to rebalance: if we are larger than
-                        * our parent, we are necessarily larger than
-                        * its other child.
-                        */
-               } else {
-                       break;
-               }
+       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;
+       check_heap(heap);
        return 0;
 }
 
@@ -189,7 +188,8 @@ void *heap_remove(struct ptr_heap *heap)
        }
        /* Shrink, replace the current max by previous last entry and heapify */
        heap_set_len(heap, heap->len - 1);
-       return heap_replace_max(heap, heap->ptrs[heap->len - 1]);
+       /* len changed. previous last entry is at heap->len */
+       return heap_replace_max(heap, heap->ptrs[heap->len]);
 }
 
 void *heap_cherrypick(struct ptr_heap *heap, void *p)
@@ -203,11 +203,13 @@ void *heap_cherrypick(struct ptr_heap *heap, void *p)
 found:
        if (heap->len == 1) {
                (void) heap_set_len(heap, 0);
+               check_heap(heap);
                return heap->ptrs[0];
        }
        /* Replace p with previous last entry and heapify. */
        heap_set_len(heap, heap->len - 1);
-       heap->ptrs[pos] = heap->ptrs[heap->len - 1];
+       /* len changed. previous last entry is at heap->len */
+       heap->ptrs[pos] = heap->ptrs[heap->len];
        heapify(heap, pos);
        return p;
 }