GARBAGE COLLECTION SYSTEM AND METHOD FOR LOCATING ROOT SET POINTERS IN METHOD ACTIVATION RECORDS

In an object oriented computer system, a root set of object references includes object references stored in the computer system's registers, as well as object references stored in activation records in the program stack. Whenever a method is invoked, a corresponding activation record is stored on the program stack. The activation record includes the invocation address for the method called as well as parameters passed to the called method. A class loader, which loads object classes into memory, determines the locations of the object references in the activation records associated with each method in a loaded object class. A list of offset values for each method activation record is stored by the class loader in a hash table data structure at a location in the hash table data structure determined by hashing the unique invocation address assigned to the method. At the beginning of each garbage collection cycle, a root set locator procedure processes each activation record in the program stack by applying a hash function to the invocation address in the activation record to determine where in the hash table data structure to locate the object reference offsets for that activation record. Using the located object reference offsets, each of the object references in the activation record is added to a root set list. The number of processor cycles required to locate and copy all the object references in activation records in the program stack is a linear function of the number of such object references.