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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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2
VERSION
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@ -1 +1 @@
B1-163-g577c54d20d+1
B1-165-gb5f4c639fd+1

2
c-host/src/app.c
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@ -187,7 +187,7 @@ static int frameThread(void * opaque)
fi->height = frame.height;
fi->stride = frame.stride;
fi->pitch = frame.pitch;
fi->offset = pageSize - sizeof(FrameBuffer);
fi->offset = pageSize - FrameBufferStructSize;
frameValid = true;
// put the framebuffer on the border of the next page

21
common/include/common/framebuffer.h
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@ -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);

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;
}
}