ralloc: Implement a new ralloc_adopt() API.

ralloc_adopt() reparents all children from one context to another.
Conceptually, ralloc_adopt(new_ctx, old_ctx) behaves like this
pseudocode:

   foreach child of old_ctx:
      ralloc_steal(new_ctx, child)

However, ralloc provides no way to iterate over a memory context's
children, and ralloc_adopt does this task more efficiently anyway.

One potential use of this is to implement a memory-sweeper pass: first,
steal all of a context's memory to a temporary context.  Then, walk over
anything that should be kept, and ralloc_steal it back to the original
context.  Finally, free the temporary context.  This works when the
context is something that can't be freed (i.e. an important structure).

Signed-off-by: Kenneth Graunke <[email protected]>
Reviewed-by: Jason Ekstrand <[email protected]>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/util/ralloc.h b/src/util/ralloc.h
index f088a36274d..01f102ba244 100644
--- a/src/util/ralloc.h
+++ b/src/util/ralloc.h
@@ -235,6 +235,13 @@ void ralloc_free(void *ptr);
 void ralloc_steal(const void *new_ctx, void *ptr);
 
 /**
+ * Reparent all children from one context to another.
+ *
+ * This effectively calls ralloc_steal(new_ctx, child) for all children of \p old_ctx.
+ */
+void ralloc_adopt(const void *new_ctx, void *old_ctx);
+
+/**
  * Return the given pointer's ralloc context.
  */
 void *ralloc_parent(const void *ptr);