A system for associating a phase with an activation of a computer program that supports garbage collection include: a plurality of stacks, each stack including at least one stack frame that includes an activation count; and a processor with logic for performing steps of: zeroing the activation count whenever the program creates a new stack frame and after garbage collection is performed; determining whether an interval has transpired during program execution; examining each stack frame's content and incrementing the activation count for each frame of the stacks once the interval has transpired; detecting the phase whose activation count is non-zero and associating the phase with the activation; and ensuring that when the phase ends, an action is immediately performed.Detecting phases in a running computer program, creates an activation count associated with each stack frame. The activation count is zeroed whenever a new frame is created in a stack and incremented for each frame encountered during periodic intervals. A phase is detected with an activation whose activation count is non-zero.