silverstripe-framework/src/Control/FlushRequestFilter.php

<?php

namespace SilverStripe\Control;

use SilverStripe\Core\Flushable;
use SilverStripe\ORM\DataModel;
use SilverStripe\Core\ClassInfo;

/**
 * Triggers a call to flush() on all implementors of Flushable.
 */
class FlushRequestFilter implements RequestFilter
{

    /**
     * @inheritdoc
     *
     * @param HTTPRequest $request
     * @param Session $session
     * @param DataModel $model
     *
     * @return bool
     */
    public function preRequest(HTTPRequest $request, Session $session, DataModel $model)
    {
        if (array_key_exists('flush', $request->getVars())) {
            foreach (ClassInfo::implementorsOf(Flushable::class) as $class) {
                $class::flush();
            }
        }

        return true;
    }

    /**
     * @inheritdoc
     *
     * @param HTTPRequest $request
     * @param HTTPResponse $response
     * @param DataModel $model
     *
     * @return bool
     */
    public function postRequest(HTTPRequest $request, HTTPResponse $response, DataModel $model)
    {
        return true;
    }
}