International Business Machines Corporation

Ethan Lewis

Elliot Karl Kolodner

Susan Patricia Paice

Martin John Trotter

Samuel David Borman

Erez Petrank

A computer system provides an object-based virtual machine environment for running successive applications. The computer system includes storage, at least a portion of which is logically divided into two or more heaps in which objects can be stored. A first heap is reset between successive applications, and a second heap persists from one application to the next. A card table is provided which comprises multiple cards, each corresponding to a region of said storage. Each card in the card table is set to null when the first heap is reset between successive applications. A card is marked whenever an object in its corresponding storage region is created or updated. It is then possible to detect potential references from the second heap to the first heap at reset by scanning the cards in the card table corresponding to the second heap, and detecting any cards which have been marked. The system further identifies any objects on the first heap which have a finalization method. The finalization methods of any such identified objects are then run on the main thread prior to reset of the first heap.

Computer system with heap reset for performing generational garbage collection implemented by card-marking between successive applications

A computer system provides an object-based environment. The computer system includes storage. A contiguous linear portion of the storage is logically divided into first and second heaps located at opposite ends of the linear portion of storage. Any gap between the two heaps represents an unallocated region of storage. The system permits references from objects on the first heap to objects on the second heap and vice versa. A garbage collector operates across both heaps to remove objects that are no longer live. Means are provided for expanding the first and second heaps into the unallocated region. The first heap is expanded according to a first expansion policy, and the second heap is expanded according to a second expansion policy.

Computer system with two heaps in contiguous storage

A method for memory management in execution of a program by a computer having a memory includes allocating respective portions of the memory to data objects using mutator threads of the program, whereby the objects are held in a heap created by the program. The data objects in the heap are traced so as to mark the data objects that are reachable at a given stage in the program. The computer loops over the mutator threads so as to verify for each of the mutator threads that every update to the allocated portions of the memory in progress by the mutator thread has been completed. The heap is then swept so as to free the memory that is allocated to the data objects that are not marked as reachable, for reallocation to new data objects.

Trace termination for on-the-fly garbage collection for weakly-consistent computer architecture

A computer system provides an object-based environment and includes storage. At least a portion of the storage is logically divided into two or more heaps in which objects can be stored. Each heap is subdivided into slices of memory. The system includes a two-level lookup structure for determining whether a given storage address corresponds to a particular heap. The lookup substructure involves a first level having one or more lookup substructures, each corresponding to a unit of memory representing a predetermined number of slices. The substructure indicates for each of these slices the particular heap, if any, that the slice belongs to. The two-level lookup structure further involves a second level for determining for a given memory address the first level lookup substructure that includes the slice containing that address.

Computer system with multiple heaps

A method for memory management in execution of a program by a computer having a memory includes setting an attribute of an unallocated unit of the memory in preparation for allocation of the memory in the unit, and allocating respective portions of the memory in the unit to data objects to be held in a heap created by the program. Responsive to the attribute that is set on the allocated portions of the memory, the data objects in the heap are traced, so as to mark the data objects that are reachable at a given stage in the program. The heap is then swept so as to free the memory that is allocated to data objects that are not marked as reachable, for reallocation to new data objects.

Elimination of coloring during object creation for concurrent garbage collection

A computer-implemented method for eliminating synchronization between sweep and allocate in respect of a newly created object in a concurrent garbage collector for a heap implemented in shared memory having mark and sweep phases. In a first collection cycle, a first attribute is associated with objects believed to be reachable and a second attribute is associated with objects believed to be unreachable, whilst for each successive collection cycle, the roles of the first and second attributes are exchanged. In accordance with conventional mark-sweep garbage collectors, the attribute is a color: usually Black and White for objects which are believed to be reachable and unreachable, respectively. Exchanging the colors for each collection cycle eliminates the overhead in synchronizing the color marking of a new object depending on whether it is located in an area of the heap that has already been swept or has yet to be swept.

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Haifa, Israel

Ethan Lewis