This is the logic to reproduce from thumb.php:
global $wgAttemptFailureEpoch;
$cache = ObjectCache::getLocalClusterInstance();
$key = $cache->makeKey(
'attempt-failures',
$wgAttemptFailureEpoch,
$file->getRepo()->getName(),
$file->getSha1(),
md5( $thumbName )
);
// Check if this file keeps failing to render
if ( $cache->get( $key ) >= 4 ) {
return [ false, wfMessage( 'thumbnail_image-failure-limit', 4 ) ];
}
$done = false;
// Record failures on PHP fatals in addition to caching exceptions
register_shutdown_function( function () use ( $cache, &$done, $key ) {
if ( !$done ) { // transform() gave a fatal
// Randomize TTL to reduce stampedes
$cache->incrWithInit( $key, $cache::TTL_HOUR + mt_rand( 0, 300 ) );
}
} );