Race condition in system_theme_data() function

There appears to be a race condition in the system_theme_data() function.

I was running several concurrent administration windows on my new Drupal-6.3 installation, and one of the loaded pages suddenly showed the following warnings:

user warning: Duplicate entry 'themes/garland/garland.info' for key 1 query: INSERT INTO system (name, owner, info, type, filename, status, throttle, bootstrap) VALUES ('garland', 'themes/engines/phptemplate/phptemplate.engine', 'a:13:{s:4:\"name\";s:7:\"Garland\";s:11:\"description\";s:66:\"Tableless, recolorable, multi-column, fluid width theme (default).\";s:7:\"version\";s:3:\"6.3\";s:4:\"core\";s:3:\"6.x\";s:6:\"engine\";s:11:\"phptemplate\";s:11:\"stylesheets\";a:2:{s:3:\"all\";a:1:{s:9:\"style.css\";s:24:\"themes/garland/style.css\";}s:5:\"print\";a:1:{s:9:\"print.css\";s:24:\"themes/garland/print.css\";}}s:7:\"project\";s:6:\"drupal\";s:9:\"datestamp\";s:10:\"1215640509\";s:7:\"regions\";a:5:{s:4:\"left\";s:12:\"Left sidebar\";s:5:\"right\";s:13:\"Right sidebar\";s:7:\"content\";s:7:\"Content\";s:6:\"header\";s:6:\"Header\";s:6:\"footer\";s:6:\"Footer\";}s:8:\"features\";a:10:{i:0;s:20:\"comment_user_picture\";i:1;s:7:\"favicon\";i:2;s:7:\"mission\";i:3;s:4:\"logo\";i:4;s:4:\"name\";i:5;s:17:\"node_user_picture\";i:6;s:6:\"search\";i:7;s:6:\"slogan\";i:8;s:13:\"primary_links\";i:9;s:15:\"secondary_links\";}s:7:\"scripts\";a:1:{s:9:\"script.js\";s:24:\"themes/garland/script.js\";}s:10:\"screenshot\";s:29:\"themes/garland/screenshot.png\";s:3:\"php\";s:5:\"4.3.5\";}', 'theme', 'themes/garland/garland.info', 0, 0, 0) in /var/www/drupal6/modules/system/system.module on line 830.
user warning: Duplicate entry 'themes/bluemarine/bluemarine.info' for key 1 query: INSERT INTO system (name, owner, info, type, filename, status, throttle, bootstrap) VALUES ('bluemarine', 'themes/engines/phptemplate/phptemplate.engine', 'a:13:{s:4:\"name\";s:10:\"Bluemarine\";s:11:\"description\";s:66:\"Table-based multi-column theme with a marine and ash color scheme.\";s:7:\"version\";s:3:\"6.3\";s:4:\"core\";s:3:\"6.x\";s:6:\"engine\";s:11:\"phptemplate\";s:7:\"project\";s:6:\"drupal\";s:9:\"datestamp\";s:10:\"1215640509\";s:7:\"regions\";a:5:{s:4:\"left\";s:12:\"Left sidebar\";s:5:\"right\";s:13:\"Right sidebar\";s:7:\"content\";s:7:\"Content\";s:6:\"header\";s:6:\"Header\";s:6:\"footer\";s:6:\"Footer\";}s:8:\"features\";a:10:{i:0;s:20:\"comment_user_picture\";i:1;s:7:\"favicon\";i:2;s:7:\"mission\";i:3;s:4:\"logo\";i:4;s:4:\"name\";i:5;s:17:\"node_user_picture\";i:6;s:6:\"search\";i:7;s:6:\"slogan\";i:8;s:13:\"primary_links\";i:9;s:15:\"secondary_links\";}s:11:\"stylesheets\";a:1:{s:3:\"all\";a:1:{s:9:\"style.css\";s:27:\"themes/bluemarine/style.css\";}}s:7:\"scripts\";a:1:{s:9:\"script.js\";s:27:\"themes/bluemarine/script.js\";}s:10:\"screenshot\";s:32:\"themes/bluemarine/screenshot.png\";s:3:\"php\";s:5:\"4.3.5\";}', 'theme', 'themes/bluemarine/bluemarine.info', 0, 0, 0) in /var/www/drupal6/modules/system/system.module on line 830.
user warning: Duplicate entry 'themes/pushbutton/pushbutton.info' for key 1 query: INSERT INTO system (name, owner, info, type, filename, status, throttle, bootstrap) VALUES ('pushbutton', 'themes/engines/phptemplate/phptemplate.engine', 'a:13:{s:4:\"name\";s:10:\"Pushbutton\";s:11:\"description\";s:52:\"Tabled, multi-column theme in blue and orange tones.\";s:7:\"version\";s:3:\"6.3\";s:4:\"core\";s:3:\"6.x\";s:6:\"engine\";s:11:\"phptemplate\";s:7:\"project\";s:6:\"drupal\";s:9:\"datestamp\";s:10:\"1215640509\";s:7:\"regions\";a:5:{s:4:\"left\";s:12:\"Left sidebar\";s:5:\"right\";s:13:\"Right sidebar\";s:7:\"content\";s:7:\"Content\";s:6:\"header\";s:6:\"Header\";s:6:\"footer\";s:6:\"Footer\";}s:8:\"features\";a:10:{i:0;s:20:\"comment_user_picture\";i:1;s:7:\"favicon\";i:2;s:7:\"mission\";i:3;s:4:\"logo\";i:4;s:4:\"name\";i:5;s:17:\"node_user_picture\";i:6;s:6:\"search\";i:7;s:6:\"slogan\";i:8;s:13:\"primary_links\";i:9;s:15:\"secondary_links\";}s:11:\"stylesheets\";a:1:{s:3:\"all\";a:1:{s:9:\"style.css\";s:27:\"themes/pushbutton/style.css\";}}s:7:\"scripts\";a:1:{s:9:\"script.js\";s:27:\"themes/pushbutton/script.js\";}s:10:\"screenshot\";s:32:\"themes/pushbutton/screenshot.png\";s:3:\"php\";s:5:\"4.3.5\";}', 'theme', 'themes/pushbutton/pushbutton.info', 0, 0, 0) in /var/www/drupal6/modules/system/system.module on line 830.
user warning: Duplicate entry 'themes/chameleon/marvin/marvin.info' for key 1 query: INSERT INTO system (name, owner, info, type, filename, status, throttle, bootstrap) VALUES ('marvin', '', 'a:13:{s:4:\"name\";s:6:\"Marvin\";s:11:\"description\";s:31:\"Boxy tabled theme in all grays.\";s:7:\"regions\";a:2:{s:4:\"left\";s:12:\"Left sidebar\";s:5:\"right\";s:13:\"Right sidebar\";}s:7:\"version\";s:3:\"6.3\";s:4:\"core\";s:3:\"6.x\";s:10:\"base theme\";s:9:\"chameleon\";s:7:\"project\";s:6:\"drupal\";s:9:\"datestamp\";s:10:\"1215640509\";s:8:\"features\";a:10:{i:0;s:20:\"comment_user_picture\";i:1;s:7:\"favicon\";i:2;s:7:\"mission\";i:3;s:4:\"logo\";i:4;s:4:\"name\";i:5;s:17:\"node_user_picture\";i:6;s:6:\"search\";i:7;s:6:\"slogan\";i:8;s:13:\"primary_links\";i:9;s:15:\"secondary_links\";}s:11:\"stylesheets\";a:1:{s:3:\"all\";a:1:{s:9:\"style.css\";s:33:\"themes/chameleon/marvin/style.css\";}}s:7:\"scripts\";a:1:{s:9:\"script.js\";s:33:\"themes/chameleon/marvin/script.js\";}s:10:\"screenshot\";s:38:\"themes/chameleon/marvin/screenshot.png\";s:3:\"php\";s:5:\"4.3.5\";}', 'theme', 'themes/chameleon/marvin/marvin.info', 0, 0, 0) in /var/www/drupal6/modules/system/system.module on line 830.
user warning: Duplicate entry 'themes/chameleon/chameleon.info' for key 1 query: INSERT INTO system (name, owner, info, type, filename, status, throttle, bootstrap) VALUES ('chameleon', 'themes/chameleon/chameleon.theme', 'a:12:{s:4:\"name\";s:9:\"Chameleon\";s:11:\"description\";s:42:\"Minimalist tabled theme with light colors.\";s:7:\"regions\";a:2:{s:4:\"left\";s:12:\"Left sidebar\";s:5:\"right\";s:13:\"Right sidebar\";}s:8:\"features\";a:4:{i:0;s:4:\"logo\";i:1;s:7:\"favicon\";i:2;s:4:\"name\";i:3;s:6:\"slogan\";}s:11:\"stylesheets\";a:1:{s:3:\"all\";a:2:{s:9:\"style.css\";s:26:\"themes/chameleon/style.css\";s:10:\"common.css\";s:27:\"themes/chameleon/common.css\";}}s:7:\"version\";s:3:\"6.3\";s:4:\"core\";s:3:\"6.x\";s:7:\"project\";s:6:\"drupal\";s:9:\"datestamp\";s:10:\"1215640509\";s:7:\"scripts\";a:1:{s:9:\"script.js\";s:26:\"themes/chameleon/script.js\";}s:10:\"screenshot\";s:31:\"themes/chameleon/screenshot.png\";s:3:\"php\";s:5:\"4.3.5\";}', 'theme', 'themes/chameleon/chameleon.info', 0, 0, 0) in /var/www/drupal6/modules/system/system.module on line 830.

Looking at the referenced code, I see the following:

function system_theme_data() {
  // Scan the installation theme .info files and their engines.
  $themes = _system_theme_data();

  // Extract current files from database.
  system_get_files_database($themes, 'theme');

  db_query("DELETE FROM {system} WHERE type = 'theme'");

  foreach ($themes as $theme) {
    if (!isset($theme->owner)) {
      $theme->owner = '';
    }

    db_query("INSERT INTO {system} (name, owner, info, type, filename, status, throttle, bootstrap) VALUES ('%s', '%s', '%s', '%s', '%s', %d, %d, %d)", $theme->name, $theme->owner, serialize($theme->inf\
o), 'theme', $theme->filename, isset($theme->status) ? $theme->status : 0, 0, 0);
  }

If two instances of this function are running concurrently, then it is possible for the two DELETE..INSERT cycles to overlap, resulting in the above warning messages.

Clearly, there should be some locking involved to prevent this from happening. Unfortunately, I don't know enough about Drupal locking semantics to suggest a fix.

Thee bug mentioned in #275801: Minor slowdown in _system_theme_data() due to typo may be contributing to the frequency at which the above function is called.