sourceRectAtTime not updating with dynamic textlayer.

//SourceText expression

var myText=[100,2000,30000];
nearestKeyIndex = 0;
if (thisLayer.marker.numKeys > 0){
nearestKeyIndex = thisLayer.marker.nearestKey(time).index;

if (thisLayer.marker.key(nearestKeyIndex).time > time){
nearestKeyIndex--;
}
}

myText[nearestKeyIndex];

///

//shapelayer size expression.

s=thisComp.layer("myTextLayer").sourceRectAtTime();
x=s.width;
y=s.height;
[x,y];

////

If i take shapelayer and connect size with text layer with source text expression using sourceRectangle. It is not updating.

Please see if someone can help.