isGoingToCrashBecauseOfMemory

<?php
class faTask extends sfBaseTask
{
    static private function getMemoryLimit()
    {
        return ini_get('memory_limit')*1024;
    }

    static private function getMemoryUsage()
    {
        return round(memory_get_usage(true)/1024,2);
    }

    static private function getMemoryUsagePercent()
    {
        return round((self::getMemoryUsage() * 100 / self::getMemoryLimit()));
    }

    static private function isGoingToCrashBecauseOfMemory($limit = 60)
    {
        return ($limit < self::getMemoryUsagePercent());
    }

    protected function execute($arguments = array(), $options = array())
    {
        // Begin the Code

        foreach ($veryBigDoctrineCollection as $doctrineRecord)
        {
            $doctrineRecord->changeMe();
            $doctrineRecord->save();
            $doctrineRecord->free();
            unset($doctrineRecord);

            if (self::isGoingToCrashBecauseOfMemory())
            {
                break;
            }
        }

        // End the Code
    }
}

Impressive!

LOL :)

You can also start a new php process which consumes a lot of memory, and test the output in the parent, like
http://github.com/rande/sfSolrPlugin/blob/master/lib/task/sfLuceneUpdateModelSystemTask.class.php#L183

you don't have to crash or break, just launch sub process like rande told you, here is my way to do it http://gist.github.com/396110