Ticket #55206: test-wp-memory-leaks.php

<?php

/**
 * Class WP_Memory_Leak_Tests
 *
 * This class tests two cases that cause memory leaks in WordPress that could
 * lead to crashes, particularly in CLI jobs that work on larger batches.  For
 * each of the cases ( one for the wpdb class and one for the global
 * $wp_object_cache ), we perform some seemingly innocuous task many times -
 * enough times to require that PHP allocate more memory because of a specific
 * action.
 *
 * Neither of the tests here show a particularly large memory increase, but I've
 * personally had both occur for me on large jobs hitting WP API functions.  The
 * one with $wpdb->queries particularly has a tendency to blow up.
 */
class WP_Memory_Leak_Tests extends \WP_UnitTestCase {

        /**
         * This tests a condition which exposes a memory leak in the WPDB class.
         * If 'SAVEQUERIES' is defined as truthy, then the $wpdb->queries property
         * can grow indefinitely.
         */
        public function test_WPDB_Memory_Leak() {

                // Once a constant is defined, it can't be undefined
                define( 'SAVEQUERIES', true );

                // I'll just start my cron job to read the import file I've got.  It's
                // got a decent number of records.
                $number_of_records = 1000;

                global $wpdb;
                $memory = memory_get_usage( true );
                $peak   = memory_get_peak_usage( true );
                foreach ( [ 'first', 'second' ] as $pass ) {
                        // first pass through, we'll apply a fix for this memory leak.
                        // second pass through, we'll bypass the fix and the tests will fail.
                        for ( $i = 1; $i <= $number_of_records; $i ++ ) {
                                if ( 'first' === $pass ) {
                                        $wpdb->queries = [];
                                }

                                // for this test, we'll do direct calls to $wpdb
                                $wpdb->query( $wpdb->prepare( "SELECT * FROM $wpdb->posts WHERE ID = %d", $i ) );
                        }
                        $this->assertEquals( $memory, memory_get_usage( true ), "$pass pass" );
                        $this->assertEquals( $peak, memory_get_peak_usage( true ), "$pass pass" );
                }

        }

        /**
         * This tests a condition which exposes a memory leak in wp cache API.  If
         * a large batch job attempts to do a lot of something that ends up caching
         * things ( like, for example, get_post or wp_insert_post ), then unless
         * the cache is flushed regularly, the memory usage grows indefinitely.
         */
        public function test_WP_Cache_Memory_Leak() {

                // I'll just start my cron job to read the import file I've got.  It's
                // got a decent number of records.
                $number_of_records = 1000;

                global $wpdb;
                $memory = memory_get_usage( true );
                $peak   = memory_get_peak_usage( true );
                foreach ( [ 'first', 'second' ] as $pass ) {
                        // first pass through, we'll apply a fix for this memory leak.
                        // second pass through, we'll bypass the fix and the tests will fail.
                        for ( $i = 1; $i <= $number_of_records; $i ++ ) {
                                if ( 'first' === $pass ) {
                                        wp_cache_flush();
                                }

                                // Because our last test defined 'SAVEQUERIES', we need to
                                // always apply this fix, otherwise that memory leak manifests.
                                // With us doing a core API function `wp_insert_post`, the number
                                // of queries is quite large and memory __really__ grows.
                                $wpdb->queries = [];

                                // let's say we're inserting posts, maybe from an excel file.
                                // this caches some things, so $wp_object_cache grows.
                                wp_insert_post([
                                        'post_type' => 'post',
                                        'post_title' => "post $i",
                                        'post_content' => "pass $pass"
                                ]);
                        }
                        $this->assertEquals( $memory, memory_get_usage( true ), "$pass pass" );
                        $this->assertEquals( $peak, memory_get_peak_usage( true ), "$pass pass" );
                }

        }

}