memory: add method to create mapped memory

Add a method to create a GstMemory with the desired mapping. Makes a copy of the
memory if it is currently in use.

gst/gstbuffer.c

@@ -963,24 +963,14 @@ gst_buffer_map (GstBuffer * buffer, GstMapInfo * info, GstMapFlags flags)
     goto not_writable;
 
   mem = gst_buffer_get_merged_memory (buffer);
-  if (mem == NULL)
+  if (G_UNLIKELY (mem == NULL))
     goto no_memory;
 
   /* now try to map */
-  if (!gst_memory_map (mem, info, flags) && write) {
+  mem = gst_memory_make_mapped (mem, info, flags);
-    GstMemory *copy;
-    /* make a (writable) copy */
-    copy = gst_memory_copy (mem, 0, -1);
-    gst_memory_unref (mem);
-    mem = copy;
   if (G_UNLIKELY (mem == NULL))
     goto cannot_map;
 
-    /* try again */
-    if (!gst_memory_map (mem, info, flags))
-      goto cannot_map;
-  }
-
   /* if the buffer is writable, replace the memory */
   if (writable)
     _replace_memory (buffer, gst_memory_ref (mem));

gst/gstmemory.c

@@ -499,6 +499,53 @@ gst_memory_unlock (GstMemory * mem)
   } while (!g_atomic_int_compare_and_exchange (&mem->state, state, newstate));
 }
 
+
+/**
+ * gst_memory_make_mapped:
+ * @mem: (transfer full): a #GstMemory
+ * @info: (out): pointer for info
+ * @flags: mapping flags
+ *
+ * Create a #GstMemory object that is mapped with @flags. If @mem is mappable
+ * with @flags, this function returns the mapped @mem directly. Otherwise a
+ * mapped copy of @mem is returned.
+ *
+ * This function takes ownership of old @mem and returns a reference to a new
+ * #GstMemory.
+ *
+ * Returns: (transfer full): a #GstMemory object mapped with @flags or NULL when
+ * a mapping is not possible.
+ */
+GstMemory *
+gst_memory_make_mapped (GstMemory * mem, GstMapInfo * info, GstMapFlags flags)
+{
+  GstMemory *result;
+
+  if (gst_memory_map (mem, info, flags)) {
+    result = mem;
+  } else {
+    result = gst_memory_copy (mem, 0, -1);
+    if (result == NULL)
+      goto cannot_copy;
+
+    if (!gst_memory_map (result, info, flags))
+      goto cannot_map;
+  }
+  return result;
+
+  /* ERRORS */
+cannot_copy:
+  {
+    GST_DEBUG ("cannot copy memory %p", mem);
+    return NULL;
+  }
+cannot_map:
+  {
+    GST_DEBUG ("cannot map memory %p with flags %d", mem, flags);
+    return NULL;
+  }
+}
+
 /**
  * gst_memory_map:
  * @mem: a #GstMemory

gst/gstmemory.h

@@ -277,6 +277,7 @@ void        gst_memory_resize      (GstMemory *mem, gssize offset, gsize size);
 /* retrieving data */
 gboolean    gst_memory_is_writable (GstMemory *mem);
 
+GstMemory * gst_memory_make_mapped (GstMemory *mem, GstMapInfo *info, GstMapFlags flags);
 gboolean    gst_memory_map         (GstMemory *mem, GstMapInfo *info, GstMapFlags flags);
 void        gst_memory_unmap       (GstMemory *mem, GstMapInfo *info);
 

win32/common/libgstreamer.def

@@ -510,6 +510,7 @@ EXPORTS
 	gst_memory_get_type
 	gst_memory_is_span
 	gst_memory_is_writable
+	gst_memory_make_mapped
 	gst_memory_map
 	gst_memory_new_wrapped
 	gst_memory_ref