Performing exact garbage collection using bitmaps that identify pointer values within objects

An apparatus for performing garbage collection for an object defined within an object oriented programming system, the object including a variable storage area for storing both pointer variables and non-pointer variables associated with the object, the apparatus comprising:

• a central processing unit;
• a memory coupled to the central processing unit;
• a tagging mechanism configured to associate a tagging bitmap with the object, each bit in the tagging bitmap specifying whether a corresponding variable in the variable storage area of the object contains a pointer variable;
• a garbage collection mechanism configured to following pointers between objects in order to determine which objects are reachable through pointers, so that other non-reachable objects can be reclaimed;
• wherein the garbage collection mechanism is configured to follow the pointer variables within the variable storage area of the object to other objects for garbage collection purposes by,
• using the tagging bitmap associated with the object to index a specific routine from a collection of routines, the collection of routines including a different routine for each possible tagging bitmap pattern, wherein the specific routine can assume by virtue of the prior indexing operation that certain variables in the variable storage area contain pointer variables, allowing the specific routine to follow the pointer variables without individually testing each variable to determine if the variable is a pointer variable, and
• executing the specific routine to follow the pointer variables in the variable storage area of the object to the other objects.

A computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for performing garbage collection for an object defined within an object oriented programming system, the object including a variable storage area for storing both pointer variables and non-pointer variables associated with the object, the method comprising:

• associating a tagging bitmap with the object, each bit in the tagging bitmap specifying whether a corresponding variable in the variable storage area of the object contains a pointer variable;
• encountering the object during a garbage collection process, which operates by following pointers between objects in order to determine which objects are reachable through pointers, so that other non-reachable objects can be reclaimed;
• and
• following the pointer variables within the variable storage area of the object to other objects for garbage collection purposes by,
• using the tagging bitmap associated with the object to index a specific routine from a collection of routines, the collection of routines including a different routine for each possible tagging bitmap pattern, wherein the specific routine can assume by virtue of the prior indexing operation that certain variables in the variable storage area contain pointer variables, allowing the specific routine to follow the pointer variables without individually testing each variable to determine if the variable is a pointer variable, and
• executing the specific routine to follow the pointer variables in the variable storage area of the object to the other objects.