src/plugin.c: Use a heap to schedule reads.

[collectd.git] / src / utils_heap.c

diff --git a/src/utils_heap.c b/src/utils_heap.c
new file mode 100644 (file)
index 0000000..1ecd07e
--- /dev/null
+++ b/src/utils_heap.c
@@ -0,0 +1,223 @@
+/**
+ * collectd - src/utils_heap.c
+ * Copyright (C) 2009  Florian octo Forster
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+ *
+ * Authors:
+ *   Florian octo Forster <octo at verplant.org>
+ **/
+
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <assert.h>
+#include <pthread.h>
+
+#include "utils_heap.h"
+
+struct c_heap_s
+{
+  pthread_mutex_t lock;
+  int (*compare) (const void *, const void *);
+
+  void **list;
+  size_t list_len; /* # entries used */
+  size_t list_size; /* # entries allocated */
+};
+
+enum reheap_direction
+{
+  DIR_UP,
+  DIR_DOWN
+};
+
+static void reheap (c_heap_t *h, size_t root, enum reheap_direction dir)
+{
+  size_t left;
+  size_t right;
+  size_t min;
+  int status;
+
+  /* Calculate the positions of the children */
+  left = (2 * root) + 1;
+  if (left >= h->list_len)
+    left = 0;
+
+  right = (2 * root) + 2;
+  if (right >= h->list_len)
+    right = 0;
+
+  /* Check which one of the children is smaller. */
+  if ((left == 0) && (right == 0))
+    return;
+  else if (left == 0)
+    min = right;
+  else if (right == 0)
+    min = left;
+  else
+  {
+    status = h->compare (h->list[left], h->list[right]);
+    if (status > 0)
+      min = right;
+    else
+      min = left;
+  }
+
+  status = h->compare (h->list[root], h->list[min]);
+  if (status <= 0)
+  {
+    /* We didn't need to change anything, so the rest of the tree should be
+     * okay now. */
+    return;
+  }
+  else /* if (status > 0) */
+  {
+    void *tmp;
+
+    tmp = h->list[root];
+    h->list[root] = h->list[min];
+    h->list[min] = tmp;
+  }
+
+  if ((dir == DIR_UP) && (root == 0))
+    return;
+
+  if (dir == DIR_UP)
+    reheap (h, root / 2, dir);
+  else if (dir == DIR_DOWN)
+    reheap (h, min, dir);
+} /* void reheap */
+
+c_heap_t *c_heap_create (int (*compare) (const void *, const void *))
+{
+  c_heap_t *h;
+
+  if (compare == NULL)
+    return (NULL);
+
+  h = malloc (sizeof (*h));
+  if (h == NULL)
+    return (NULL);
+
+  memset (h, 0, sizeof (*h));
+  pthread_mutex_init (&h->lock, /* attr = */ NULL);
+  h->compare = compare;
+  
+  h->list = NULL;
+  h->list_len = 0;
+  h->list_size = 0;
+
+  return (h);
+} /* c_heap_t *c_heap_create */
+
+void c_heap_destroy (c_heap_t *h)
+{
+  if (h == NULL)
+    return;
+
+  h->list_len = 0;
+  h->list_size = 0;
+  free (h->list);
+  h->list = NULL;
+
+  pthread_mutex_destroy (&h->lock);
+
+  free (h);
+} /* void c_heap_destroy */
+
+int c_heap_insert (c_heap_t *h, void *ptr)
+{
+  if ((h == NULL) || (ptr == NULL))
+    return (-EINVAL);
+
+  pthread_mutex_lock (&h->lock);
+
+  assert (h->list_len <= h->list_size);
+  if (h->list_len == h->list_size)
+  {
+    void **tmp;
+
+    tmp = realloc (h->list, (h->list_size + 16) * sizeof (*h->list));
+    if (tmp == NULL)
+    {
+      pthread_mutex_unlock (&h->lock);
+      return (-ENOMEM);
+    }
+
+    h->list = tmp;
+    h->list_size += 16;
+  }
+
+  /* Insert the new node as a leaf. */
+  h->list[h->list_len] = ptr;
+  h->list_len++;
+
+  /* Reorganize the heap from bottom up. */
+  reheap (h, /* parent of this node = */ (h->list_len - 1) / 2, DIR_UP);
+  
+  pthread_mutex_unlock (&h->lock);
+  return (0);
+} /* int c_heap_insert */
+
+void *c_head_get_root (c_heap_t *h)
+{
+  void *ret = NULL;
+
+  if (h == NULL)
+    return (NULL);
+
+  pthread_mutex_lock (&h->lock);
+
+  if (h->list_len == 0)
+  {
+    pthread_mutex_unlock (&h->lock);
+    return (NULL);
+  }
+  else if (h->list_len == 1)
+  {
+    ret = h->list[0];
+    h->list[0] = NULL;
+    h->list_len = 0;
+  }
+  else /* if (h->list_len > 1) */
+  {
+    ret = h->list[0];
+    h->list[0] = h->list[h->list_len - 1];
+    h->list[h->list_len - 1] = NULL;
+    h->list_len--;
+
+    reheap (h, /* root = */ 0, DIR_DOWN);
+  }
+
+  /* free some memory */
+  if ((h->list_len + 32) < h->list_size)
+  {
+    void **tmp;
+
+    tmp = realloc (h->list, (h->list_len + 16) * sizeof (*h->list));
+    if (tmp != NULL)
+    {
+      h->list = tmp;
+      h->list_size = h->list_len + 16;
+    }
+  }
+
+  pthread_mutex_unlock (&h->lock);
+
+  return (ret);
+} /* void *c_head_get_root */
+
+/* vim: set sw=2 sts=2 et fdm=marker : */