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<title>[60400] trunk/src/wp-includes/blocks.php: do_blocks(): Document transient-memory-leak optimization.</title>
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<dt style="float: left; width: 6em; font-weight: bold">Revision</dt> <dd><a style="font-weight: bold" href="https://core.trac.wordpress.org/changeset/60400">60400</a><script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","description":"Review this Commit","action":{"@type":"ViewAction","url":"https://core.trac.wordpress.org/changeset/60400","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>dmsnell</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2025-07-01 15:59:12 +0000 (Tue, 01 Jul 2025)</dd>
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<pre style='padding-left: 1em; margin: 2em 0; border-left: 2px solid #ccc; line-height: 1.25; font-size: 105%; font-family: sans-serif'>do_blocks(): Document transient-memory-leak optimization.
Adds explanatory comment indicating why the optimization was added
and guarding against accidental removal.
This is a documentation-only change and should include no functional
or visual changes.
Props audrasjb, dmsnell, joemcgill, sirlouen, westonruter, zunaid321.
Follow-up to <a href="https://core.trac.wordpress.org/changeset/60316">[60316]</a>.
Fixes <a href="https://core.trac.wordpress.org/ticket/63588">#63588</a>.</pre>
<h3>Modified Paths</h3>
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<li><a href="#trunksrcwpincludesblocksphp">trunk/src/wp-includes/blocks.php</a></li>
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<h3>Diff</h3>
<a id="trunksrcwpincludesblocksphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/src/wp-includes/blocks.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/src/wp-includes/blocks.php 2025-07-01 15:38:44 UTC (rev 60399)
+++ trunk/src/wp-includes/blocks.php 2025-07-01 15:59:12 UTC (rev 60400)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -2408,6 +2408,25 @@
</span><span class="cx" style="display: block; padding: 0 10px"> $top_level_block_count = count( $blocks );
</span><span class="cx" style="display: block; padding: 0 10px"> $output = '';
</span><span class="cx" style="display: block; padding: 0 10px">
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ /**
+ * 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.
+ */
</ins><span class="cx" style="display: block; padding: 0 10px"> for ( $i = 0; $i < $top_level_block_count; $i++ ) {
</span><span class="cx" style="display: block; padding: 0 10px"> $output .= render_block( $blocks[ $i ] );
</span><span class="cx" style="display: block; padding: 0 10px"> $blocks[ $i ] = null;
</span></span></pre>
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