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Instruments:

https://developer.apple.com/library/mac/documentation/Develo...

Which for some features it just a fancy UI on top of dtrace, but still a good way to get started with these kinds of things.

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Fancy UI or not, it is an absolutely invaluable tool when profiling code on OS X. The memory leak detector is really neat too, and has helped me numerous times track down where I am leaking memory.

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