disclosed is a garbage collection algorithm that achieves hierarchical copy order with parallel garbage collection threads . more specifically , the present invention provides a garbage collection method and system for copying objects from a from - space to a to - space . the method comprises the steps of having multiple threads that simultaneously perform work for garbage collection , examining the placement of objects on blocks , and changing the placement of objects on blocks based on step . preferably , the method includes the additional step of calculating a placement of object based on step , and using the result of the calculation for step . for example , the calculation may be used to increase the frequency of intra - block pointers and / or to increase the frequency of siblings on the same block .