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[common] fix FrameBuffer to use atomics correctly

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Might Fix #248
This commit is contained in:
Geoffrey McRae
2020-04-12 13:14:53 +10:00
parent b5f4c639fd
commit 1222fd40b7
4 changed files with 39 additions and 21 deletions
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35
common/src/framebuffer.c
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@@ -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;
}
}