First of all, strict and warnings could help you a lot... making sure all of your variables are defined. Whenever you have variables used only in a loop, it is good to define them with my in that loop, so they get cleaned up when they go out of scope...

looking at your code I am guessing your leak is in

$spy[$ct]=$global[$x];
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$ct just keeps getting incremented, so @spy just keeps getting bigger and bigger, and never clears out. There may be other things, but that is what I see from a quick look.

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