[FFmpeg-devel] [PATCH] idctdsp: make ff_add/put_pixels_clamped function pointers atomic.

[Ronald S. Bultje]

This fixes the following tsan warnings when running fate-dnxhr-parse:

WARNING: ThreadSanitizer: data race (pid=29917)
  Write of size 8 at 0x0000025b12d8 by thread T2 (mutexes: write M1543):
    #0 ff_idctdsp_init src/libavcodec/idctdsp.c:313 (ffmpeg+0x00000044b68e)
[..]
  Previous write of size 8 at 0x0000025b12d8 by thread T1 (mutexes: write M1541):
    #0 ff_idctdsp_init src/libavcodec/idctdsp.c:313 (ffmpeg+0x00000044b68e)
---
 libavcodec/idctdsp.c |  8 ++++----
 libavcodec/idctdsp.h | 17 +++++++++++++++--
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/libavcodec/idctdsp.c b/libavcodec/idctdsp.c
index 84dd645..9bcf8ae 100644
--- a/libavcodec/idctdsp.c
+++ b/libavcodec/idctdsp.c
@@ -80,8 +80,8 @@ av_cold void ff_init_scantable_permutation(uint8_t *idct_permutation,
     }
 }
 
-void (*ff_put_pixels_clamped)(const int16_t *block, uint8_t *pixels, ptrdiff_t line_size);
-void (*ff_add_pixels_clamped)(const int16_t *block, uint8_t *pixels, ptrdiff_t line_size);
+atomic_uintptr_t ff_put_pixels_clamped_fn_ptr;
+atomic_uintptr_t ff_add_pixels_clamped_fn_ptr;
 
 static void put_pixels_clamped_c(const int16_t *block, uint8_t *av_restrict pixels,
                                  ptrdiff_t line_size)
@@ -310,8 +310,8 @@ av_cold void ff_idctdsp_init(IDCTDSPContext *c, AVCodecContext *avctx)
     if (ARCH_MIPS)
         ff_idctdsp_init_mips(c, avctx, high_bit_depth);
 
-    ff_put_pixels_clamped = c->put_pixels_clamped;
-    ff_add_pixels_clamped = c->add_pixels_clamped;
+    atomic_store(&ff_put_pixels_clamped_fn_ptr, (uintptr_t) c->put_pixels_clamped);
+    atomic_store(&ff_add_pixels_clamped_fn_ptr, (uintptr_t) c->add_pixels_clamped);
 
     ff_init_scantable_permutation(c->idct_permutation,
                                   c->perm_type);
diff --git a/libavcodec/idctdsp.h b/libavcodec/idctdsp.h
index f9ba6c3..16595fc 100644
--- a/libavcodec/idctdsp.h
+++ b/libavcodec/idctdsp.h
@@ -19,6 +19,7 @@
 #ifndef AVCODEC_IDCTDSP_H
 #define AVCODEC_IDCTDSP_H
 
+#include <stdatomic.h>
 #include <stdint.h>
 
 #include "config.h"
@@ -97,8 +98,20 @@ typedef struct IDCTDSPContext {
     enum idct_permutation_type perm_type;
 } IDCTDSPContext;
 
-extern void (*ff_put_pixels_clamped)(const int16_t *block, uint8_t *pixels, ptrdiff_t line_size);
-extern void (*ff_add_pixels_clamped)(const int16_t *block, uint8_t *pixels, ptrdiff_t line_size);
+typedef void (*px_clamp_fn)(const int16_t *block, uint8_t *pixels,
+                            ptrdiff_t line_size);
+
+#define ff_put_pixels_clamped ff_put_pixels_clamped_get_fn_ptr()
+extern atomic_uintptr_t ff_put_pixels_clamped_fn_ptr;
+static av_always_inline px_clamp_fn ff_put_pixels_clamped_get_fn_ptr(void) {
+    return (px_clamp_fn) atomic_load(&ff_put_pixels_clamped_fn_ptr);
+}
+
+#define ff_add_pixels_clamped ff_add_pixels_clamped_get_fn_ptr()
+extern atomic_uintptr_t ff_add_pixels_clamped_fn_ptr;
+static av_always_inline px_clamp_fn ff_add_pixels_clamped_get_fn_ptr(void) {
+    return (px_clamp_fn) atomic_load(&ff_add_pixels_clamped_fn_ptr);
+}
 
 void ff_idctdsp_init(IDCTDSPContext *c, AVCodecContext *avctx);
 
-- 
2.8.1