Method of deterministic garbage collection

Abstract

A garbage collection method that distinguishes between local objects and managed objects, and between an ordinary pointer to an object, an owning pointer to an object, and a non-owning pointer to an object is presented. Ordinary pointers point only to local objects, and owning and non-owning pointers point only to managed objects. Managed objects have attributes including a count of the number of owning pointers referring to them, and a linked list of non-owning pointers referring to them. Managed objects only possess non-owning pointers. Only an invocation of a subroutine within a thread can possess an owning pointer. Using this method, when an invocation exits, its exit code gives up ownership of all objects it owned. When an object is no longer reachable from any owning pointer, either directly, or indirectly through non-owning pointers, the object is immediately de-allocated. By implementing data structures and methods to support owning pointers, non-owning pointers, and managed objects, and by enforcing rules regarding the use of ordinary pointers, owning pointers, and non-owning pointers, efficient and deterministic garbage collection is achieved, memory leaks and dangling pointers are eliminated, and objects containing circular references to each other are not a source of memory leaks.

Description

[0001] A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.BACKGROUND OF THE INVENTION

[0002] This invention relates generally to programming of digital computers, and, more specifically, to memory management and garbage collection.

[0003] There are presently two broad approaches to memory management: (1) programmer memory management where programmers are responsible for writing explicit program code to de-allocate memory for the storage of objects no longer needed by a program; and (2) automatic memory management where the de-allocation of memory is done automatically, after the system determines that objects are no longer needed.

[0004] If memory management is automatic, there is...

Examples

Embodiment Construction

[0023]The present invention specifies an invocation, an owning pointer, a non-owning pointer, and a managed object. In the preferred embodiment, these are modeled using statements of an object-oriented programming language as classes with the names Invocation, OwningPointer, NonOwningPointer, and ManagedObject, respectively. FIG. 1 shows these classes using the graphical symbols of the Unified Modeling Language (UML), as defined by Rumbaugh, James, Ivar Jacobson, and Grady Booch, “The Unified Modeling Language Reference Manual,” Reading, Mass., Addison-Wesley, 1999, which is incorporated herein by reference.

[0024]An invocation is an invocation of a subroutine within a thread of a process of a system. An invocation ceases to exist when it is exited. An owning pointer is a pointer from an invocation to a managed object that establishes an ownership relationship between the invocation and the managed object. The owner of an owning pointer owns the managed object to which it points. A n...

[0001] A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.BACKGROUND OF THE INVENTION

[0002] This invention relates generally to programming of digital computers, and, more specifically, to memory management and garbage collection.

[0003] There are presently two broad approaches to memory management: (1) programmer memory management where programmers are responsible for writing explicit program code to de-allocate memory for the storage of objects no longer needed by a program; and (2) automatic memory management where the de-allocation of memory is done automatically, after the system determines that objects are no longer needed.

[0004] If memory management is automatic, there is...

Examples

Embodiment Construction

[0023]The present invention specifies an invocation, an owning pointer, a non-owning pointer, and a managed object. In the preferred embodiment, these are modeled using statements of an object-oriented programming language as classes with the names Invocation, OwningPointer, NonOwningPointer, and ManagedObject, respectively. FIG. 1 shows these classes using the graphical symbols of the Unified Modeling Language (UML), as defined by Rumbaugh, James, Ivar Jacobson, and Grady Booch, “The Unified Modeling Language Reference Manual,” Reading, Mass., Addison-Wesley, 1999, which is incorporated herein by reference.

[0024]An invocation is an invocation of a subroutine within a thread of a process of a system. An invocation ceases to exist when it is exited. An owning pointer is a pointer from an invocation to a managed object that establishes an ownership relationship between the invocation and the managed object. The owner of an owning pointer owns the managed object to which it points. A n...

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