[common] added new ringbuffer helper for metrics collection

common/CMakeLists.txt

@@ -29,6 +29,7 @@ set(COMMON_SOURCES
   src/KVMFR.c
   src/countedbuffer.c
   src/runningavg.c
+  src/ringbuffer.c
 )
 
 add_library(lg_common STATIC ${COMMON_SOURCES})

common/include/common/ringbuffer.h

@@ -0,0 +1,32 @@
+/**
+ * Looking Glass
+ * Copyright (C) 2017-2021 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * 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., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include <stddef.h>
+
+typedef struct RingBuffer * RingBuffer;
+
+RingBuffer ringbuffer_new(int length, size_t valueSize);
+void ringbuffer_free(RingBuffer * rb);
+void ringbuffer_push(RingBuffer rb, const void * value);
+void ringbuffer_reset(RingBuffer rb);
+
+int    ringbuffer_getStart (const RingBuffer rb);
+int    ringbuffer_getCount (const RingBuffer rb);
+void * ringbuffer_getValues(const RingBuffer rb);

common/src/ringbuffer.c

@@ -0,0 +1,85 @@
+/**
+ * Looking Glass
+ * Copyright (C) 2017-2021 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * 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., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include "common/ringbuffer.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+struct RingBuffer
+{
+  int     length;
+  size_t  valueSize;
+  int     start, pos, count;
+  char    values[0];
+};
+
+RingBuffer ringbuffer_new(int length, size_t valueSize)
+{
+  struct RingBuffer * rb = calloc(1, sizeof(*rb) + valueSize * length);
+  rb->length    = length;
+  rb->valueSize = valueSize;
+  return rb;
+}
+
+void ringbuffer_free(RingBuffer * rb)
+{
+  if (!*rb)
+    return;
+
+  free(*rb);
+  *rb = NULL;
+}
+
+void ringbuffer_push(RingBuffer rb, const void * value)
+{
+  if (rb->count < rb->length)
+    ++rb->count;
+  else
+    if (++rb->start == rb->length)
+      rb->start = 0;
+
+  memcpy(rb->values + rb->pos * rb->valueSize, value, rb->valueSize);
+
+  if (++rb->pos == rb->length)
+    rb->pos = 0;
+}
+
+void ringbuffer_reset(RingBuffer rb)
+{
+  rb->start = 0;
+  rb->pos   = 0;
+  rb->count = 0;
+}
+
+int ringbuffer_getStart(const RingBuffer rb)
+{
+  return rb->start;
+}
+
+int ringbuffer_getCount(const RingBuffer rb)
+{
+  return rb->count;
+}
+
+void * ringbuffer_getValues(const RingBuffer rb)
+{
+  return rb->values;
+}