pointcache: add PointCache utility class

This is a simple cache that keeps x,y pairs for use when drawing
visualizers. To keep this generic, and save on memory, we simply
store the x,y coordinates as floats between 0.0 and 1.0. This
saves us roughly 50% on each data point over the 2 8-byte
numbers we would otherwise store.

Obviously, we could take this further and make some fancy index
storage with run-length-encode values, but this should work for
now and allow us to get more exotic later.

lib/Makefile.am

@@ -18,6 +18,8 @@ libutil_la_SOURCES = \
 	util/demangle.h \
 	util/elfparser.c \
 	util/elfparser.h \
+	util/pointcache.c \
+	util/pointcache.h \
 	util/stackstash.c \
 	util/stackstash.h \
 	$(NULL)

lib/util/pointcache.c

@@ -0,0 +1,103 @@
+/* pointcache.c
+ *
+ * Copyright (C) 2016 Christian Hergert <chergert@redhat.com>
+ *
+ * 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 3 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#define G_LOG_DOMAIN "pointcache"
+
+#include "pointcache.h"
+
+struct _PointCache
+{
+  volatile gint ref_count;
+  GHashTable *sets;
+};
+
+static void
+point_cache_destroy (PointCache *self)
+{
+  g_clear_pointer (&self->sets, g_hash_table_unref);
+  g_slice_free (PointCache, self);
+}
+
+PointCache *
+point_cache_ref (PointCache *self)
+{
+  g_return_val_if_fail (self->ref_count > 0, NULL);
+  g_atomic_int_inc (&self->ref_count);
+  return self;
+}
+
+void
+point_cache_unref (PointCache *self)
+{
+  g_return_if_fail (self->ref_count > 0);
+  if (g_atomic_int_dec_and_test (&self->ref_count))
+    point_cache_destroy (self);
+}
+
+PointCache *
+point_cache_new (void)
+{
+  PointCache *self;
+
+  self = g_slice_new0 (PointCache);
+  self->ref_count = 1;
+  self->sets = g_hash_table_new_full (NULL, NULL, NULL, (GDestroyNotify)g_array_unref);
+
+  return self;
+}
+
+void
+point_cache_add_set (PointCache *self,
+                     guint       set_id)
+{
+  g_hash_table_insert (self->sets,
+                       GUINT_TO_POINTER (set_id),
+                       g_array_new (FALSE, FALSE, sizeof (Point)));
+}
+
+gboolean
+point_cache_contains_set (PointCache *self,
+                          guint       set_id)
+{
+  return g_hash_table_contains (self->sets, GUINT_TO_POINTER (set_id));
+}
+
+void
+point_cache_add_point_to_set (PointCache *self,
+                              guint       set_id,
+                              gfloat      x,
+                              gfloat      y)
+{
+  GArray *ar;
+  Point point = { x, y };
+
+  ar = g_hash_table_lookup (self->sets, GUINT_TO_POINTER (set_id));
+  g_array_append_val (ar, point);
+}
+
+const Point *
+point_cache_get_points (PointCache *self,
+                        guint       set_id,
+                        guint      *n_points)
+{
+  GArray *ar;
+
+  ar = g_hash_table_lookup (self->sets, GUINT_TO_POINTER (set_id));
+  *n_points = ar->len;
+  return &g_array_index (ar, const Point, 0);
+}

lib/util/pointcache.h

@@ -0,0 +1,53 @@
+/* pointcache.h
+ *
+ * Copyright (C) 2016 Christian Hergert <chergert@redhat.com>
+ *
+ * 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 3 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef POINT_CACHE_H
+#define POINT_CACHE_H
+
+#include <glib.h>
+
+G_BEGIN_DECLS
+
+typedef struct _PointCache PointCache;
+
+typedef struct
+{
+  gfloat x;
+  gfloat y;
+} Point;
+
+PointCache  *point_cache_new              (void);
+PointCache  *point_cache_ref              (PointCache *self);
+void         point_cache_unref            (PointCache *self);
+void         point_cache_add_set          (PointCache *self,
+                                           guint       set_id);
+gboolean     point_cache_contains_set     (PointCache *self,
+                                           guint       set_id);
+void         point_cache_add_point_to_set (PointCache *self,
+                                           guint       set_id,
+                                           gfloat      x,
+                                           gfloat      y);
+const Point *point_cache_get_points       (PointCache *self,
+                                           guint       set_id,
+                                           guint      *n_points);
+
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (PointCache, point_cache_unref)
+
+G_END_DECLS
+
+#endif /* POINT_CACHE_H */