Changeset 60435

Timestamp:

07/08/2025 09:00:01 AM (6 months ago)

Author:

audrasjb

Message:

Editor: Free up transient memory leak in do_blocks().

There has been a memory inefficiency inside of do_blocks() where it
parses the given content then iterates through each top-level block to
render it. Unfortunately each top-level block can considerably add to
the overall memory use involved, and once moving on to the next
top-level block, all of the allocated memory will be retained until the
end of the call to do_blocks().

In this change, each parsed block sub-tree is freed via reset to null
after it has been rendered. All top-level blocks are rendered
independently of each other and so this operation is safe — there are no
data dependencies between them.

This commit also includes follow-up changes committed in [60400] and [60402].

Rewieved by audrasjb.
Merges [60316], [60400] and [60402] to the 6.8 branch.
Props dmsnell, joemcgill.
Fixes #63588.

Location:

branches/6.8

Files:

• . (modified) (1 prop)
• src/wp-includes/blocks.php (modified) (1 diff)

branches/6.8/src/wp-includes/blocks.php

@@ -2405 +2405 @@
  */
 function do_blocks( $content ) {
-    $blocks = parse_blocks( $content );
-    $output = '';
-
-    foreach ( $blocks as $block ) {
-        $output .= render_block( $block );
+    $blocks                = parse_blocks( $content );
+    $top_level_block_count = count( $blocks );
+    $output                = '';
+
+    /**
+     * Parsed blocks consist of a list of top-level blocks. Those top-level
+     * blocks may themselves contain nested inner blocks. However, every
+     * top-level block is rendered independently, meaning there are no data
+     * dependencies between them.
+     *
+     * Ideally, therefore, the parser would only need to parse one complete
+     * top-level block at a time, render it, and move on. Unfortunately, this
+     * is not possible with {@see \parse_blocks()} because it must parse the
+     * entire given document at once.
+     *
+     * While the current implementation prevents this optimization, it’s still
+     * possible to reduce the peak memory use when calls to `render_block()`
+     * on those top-level blocks are memory-heavy (which many of them are).
+     * By setting each parsed block to `NULL` after rendering it, any memory
+     * allocated during the render will be freed and reused for the next block.
+     * Before making this change, that memory was retained and would lead to
+     * out-of-memory crashes for certain posts that now run with this change.
+     */
+    for ( $i = 0; $i < $top_level_block_count; $i++ ) {
+        $output      .= render_block( $blocks[ $i ] );
+        $blocks[ $i ] = null;
     }