[FFmpeg-devel] [PATCH 1/4] lavu/buffer: add a convenience function for replacing buffers

[Anton Khirnov]

A common pattern e.g. in libavcodec is replacing/updating buffer
references: unref old one, ref new one. This function allows simplifying
such code an avoiding unnecessary refs+unrefs if the references are
already equivalent.
---
 doc/APIchanges     |  3 +++
 libavutil/buffer.c | 22 ++++++++++++++++++++++
 libavutil/buffer.h | 17 +++++++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/doc/APIchanges b/doc/APIchanges
index fb5534b5f5..757d814eee 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -15,6 +15,9 @@ libavutil:     2017-10-21
 
 API changes, most recent first:
 
+2020-xx-xx - xxxxxxxxxx - lavc 56.50.100 - buffer.h
+  Add a av_buffer_replace() convenience function.
+
 2020-xx-xx - xxxxxxxxxx - lavc 58.88.100 - avcodec.h codec.h
   Move AVCodec-related public API to new header codec.h.
 
diff --git a/libavutil/buffer.c b/libavutil/buffer.c
index 6d9cb7428e..ecd83da9c3 100644
--- a/libavutil/buffer.c
+++ b/libavutil/buffer.c
@@ -216,6 +216,28 @@ int av_buffer_realloc(AVBufferRef **pbuf, int size)
     return 0;
 }
 
+int av_buffer_replace(AVBufferRef **pdst, AVBufferRef *src)
+{
+    AVBufferRef *dst = *pdst;
+
+    if (!src) {
+        av_buffer_unref(pdst);
+        return !!dst;
+    }
+
+    if (dst && dst->buffer == src->buffer) {
+        /* make sure the data pointers match */
+        dst->data = src->data;
+        dst->size = src->size;
+        return 0;
+    }
+
+    av_buffer_unref(pdst);
+    *pdst = av_buffer_ref(src);
+
+    return *pdst ? 1 : AVERROR(ENOMEM);
+}
+
 AVBufferPool *av_buffer_pool_init2(int size, void *opaque,
                                    AVBufferRef* (*alloc)(void *opaque, int size),
                                    void (*pool_free)(void *opaque))
diff --git a/libavutil/buffer.h b/libavutil/buffer.h
index e0f94314f4..497dc98c20 100644
--- a/libavutil/buffer.h
+++ b/libavutil/buffer.h
@@ -197,6 +197,23 @@ int av_buffer_make_writable(AVBufferRef **buf);
  */
 int av_buffer_realloc(AVBufferRef **buf, int size);
 
+/**
+ * Ensure dst refers to the same data as src.
+ *
+ * When *dst is already equivalent to src, do nothing. Otherwise unreference dst
+ * and replace it with a new reference to src.
+ *
+ * @param dst Pointer to either a valid buffer reference or NULL. On success,
+ *            this will point to a buffer reference equivalent to src. On
+ *            failure, dst will be unreferenced.
+ * @param src A buffer reference to replace dst with. May be NULL, then this
+ *            function is equivalent to av_buffer_unref(dst).
+ * @return 0 if dst was equivalent to src on input and nothing was done
+ *         1 if dst was replaced with a new reference to src
+ *         A negative error code on failure.
+ */
+int av_buffer_replace(AVBufferRef **dst, AVBufferRef *src);
+
 /**
  * @}
  */
-- 
2.26.2