[common] fix FrameBuffer to use atomics correctly

Might Fix #248

common/include/common/framebuffer.h

@@ -23,24 +23,19 @@ Place, Suite 330, Boston, MA 02111-1307 USA
 #include <stdbool.h>
 #include <stdint.h>
 
-
-typedef struct stFrameBuffer
-{
-  uint64_t  wp;
-  uint8_t   data[0];
-}
-FrameBuffer;
-
+typedef struct stFrameBuffer FrameBuffer;
 
 typedef bool (*FrameBufferReadFn)(void * opaque, const void * src, size_t size);
 
+/**
+ * The size of the FrameBuffer struct
+ */
+extern const size_t FrameBufferStructSize;
+
 /**
  * Wait for the framebuffer to fill to the specified size
  */
-static inline void framebuffer_wait(const FrameBuffer * frame, size_t size)
-{
-  while(frame->wp != size) {}
-}
+void framebuffer_wait(const FrameBuffer * frame, size_t size);
 
 /**
  * Read data from the KVMFRFrame into the dst buffer
@@ -60,4 +55,4 @@ void framebuffer_prepare(FrameBuffer * frame);
 /**
  * Write data from the src buffer into the KVMFRFrame
  */
-bool framebuffer_write(FrameBuffer * frame, const void * src, size_t size);
+bool framebuffer_write(FrameBuffer * frame, const void * src, size_t size);

common/src/framebuffer.c

@@ -21,19 +21,38 @@ Place, Suite 330, Boston, MA 02111-1307 USA
 #include "common/debug.h"
 
 #include <string.h>
+#include <stdatomic.h>
+
 #define FB_CHUNK_SIZE 1024
 
+struct stFrameBuffer
+{
+  atomic_uint_least32_t wp;
+  uint8_t               data[0];
+};
+
+const size_t FrameBufferStructSize = sizeof(FrameBuffer);
+
+void framebuffer_wait(const FrameBuffer * frame, size_t size)
+{
+  while(atomic_load_explicit(&frame->wp, memory_order_relaxed) != size) {}
+}
+
 bool framebuffer_read(const FrameBuffer * frame, void * dst, size_t size)
 {
   uint8_t *d  = (uint8_t*)dst;
   uint64_t rp = 0;
   while(rp < size)
   {
+    uint_least32_t wp;
+
     /* spinlock */
-    while(rp == frame->wp) { }
+    do
+      wp = atomic_load_explicit(&frame->wp, memory_order_relaxed);
+    while(rp == wp);
 
     /* copy what we can */
-    uint64_t avail = frame->wp - rp;
+    uint64_t avail = wp - rp;
     avail = avail > size ? size : avail;
 
     memcpy(d, frame->data + rp, avail);
@@ -50,11 +69,15 @@ bool framebuffer_read_fn(const FrameBuffer * frame, FrameBufferReadFn fn, size_t
   uint64_t rp = 0;
   while(rp < size)
   {
+    uint_least32_t wp;
+
     /* spinlock */
-    while(rp == frame->wp) { }
+    do
+      wp = atomic_load_explicit(&frame->wp, memory_order_relaxed);
+    while(rp == wp);
 
     /* copy what we can */
-    uint64_t avail = frame->wp - rp;
+    uint64_t avail = wp - rp;
     avail = avail > size ? size : avail;
 
     if (!fn(opaque, frame->data + rp, avail))
@@ -82,8 +105,8 @@ bool framebuffer_write(FrameBuffer * frame, const void * src, size_t size)
   {
     size_t copy = size < FB_CHUNK_SIZE ? FB_CHUNK_SIZE : size;
     memcpy(frame->data + frame->wp, src, copy);
-    __sync_fetch_and_add(&frame->wp, copy);
+    atomic_fetch_add(&frame->wp, copy);
     size -= copy;
   }
   return true;
-}
+}