International Business Machines Corporation

Daryl James Maier

Ryan Andrew Sciampacone

Peter Wiebe Burka

Aleksandar Micic

Jeffrey Michael Disher

David Kevin Siegwart

Marcel Mitran

Vijay Sundaresan

Nikola Grcevski

Nikola Groevski

A technique for incrementally unloading classes using a region-based garbage collector is described. One aspect of such a technique includes maintaining a remembered set for a class set. The remembered set indicates whether instances of the class set are contained in one or more regions in memory, and in which regions the instances are contained. Upon performing an incremental garbage collection process for a subset of the regions in memory, the technique examines the remembered set to determine whether the class set includes instances in regions outside of the subset. If the remembered set indicates that the class set includes instances outside of the subset of regions, the technique identifies the class set as 'live.' This will preclude unloading the class set from the subset of regions.

Incremental class unloading in a region-based garbage collector

A method to implement parallel, single-pass compaction in a garbage collector is described. In one embodiment, such a method includes conducting a planning phase for multiple regions to be compacted. During the planning phase, the method determines new locations for data entities in the multiple regions. The method then performs a move phase for the multiple regions to move the data entities to their new locations. During the move phase, the method initiates multiple compaction threads to move the data entities to their new locations. While executing, the compaction threads dynamically build a dependency graph of the regions being compacted. The dependency graph guarantees that no data entity is moved to its new location until all data entities that it overwrites have been moved to their new locations. A corresponding computer program product and apparatus are also disclosed herein.

Parallel, single-pass compaction in a region-based garbage collector

Automatic memory management with a generational copy collector garbage collection algorithm running on parallel threads to perform simultaneous and independent copying and scanning. An object is scanned. It is determined whether an object referenced within the slot of the object being scanned may be copied to the same generation as the scanned object. A mark may be made to indicate that the referenced object may be copied to a different generation than the scanned object. The mark defers the copying of the referenced object.

Defer separating children in parallel copying garbage collection

An illustrative embodiment of a computer-implemented process for compaction planning selects a source region from a set of regions to form a selected source region, initializes process data using information from the selected source region and responsive to a determination that a current destination is not NULL and not full, determines whether to atomically consume from a destination. Responsive to a determination to atomically consume from a destination, the computer-implemented process plans to evacuate into a consumed extent and updates the process data and responsive to a determination that the source region is empty, determines whether more work remains. Responsive to a determination that more work does not remain, the computer-implemented process generates a relocation table.

Compaction planning

A computer-implementable method, system and apparatus. The frequency of reference to an object, also known as 'hotness,' can be collected as a part of a profiling phase during a runtime operation of data-processing system by permitting each reference to the object during the runtime operation to randomly guess a predetermined value associated with the object, such that a correct guess thereof implies that the object is referenced frequently. Thereafter, the frequency of reference to the object can be validated by identifying a particular value in a header associated with the object, in response to collecting the frequency of reference to the object during the profiling phase, thereby increasing the scalability and efficiency of the runtime operation while permitting data associated with the frequency of reference to the object to other applications for immediate use.

Efficient object profiling for optimizing object locality

An illustrative embodiment of a computer-implemented process for dynamic measurement and adaptation of a parallel copying garbage collector initializes values and data structures, receives an evacuate set, determines whether a new copy block is required and responsive to a determination that a new copy block is required, calculates a size of the new copy block. The computer-implemented process further selects a survivor region from a list of survivor regions to form a selected survivor region, places a lock on the selected survivor region, identifies a number of threads enqueued on the selected survivor region, responsive to a determination that a contention value exceeds a predetermined value, increases a size of the list of survivor regions, evacuates blocks to the selected survivor region and responsive to a determination that more evacuate blocks do not exist, terminates.

Dynamic measurement and adaptation of a copying garbage collector

An operating system or virtual machine of an information handling system (IHS) initializes a garbage collector to provide object memory compaction during application execution. The operating system or virtual machine performs move and fixup management within heap or object memory stores. The garbage collector identifies holes or unused portions of heap memory and moves one or more objects during compaction operations. After the garbage collector moves the object, a fixup cache tool fixes up the object pointers within the object. The fixup cache tool maintains a fixup cache that includes pointer information corresponding to the objects that the garbage collector moves. The fixup cache tool employs the pointer information within the fixup cache to update or otherwise fixup the objects within the heap that the garbage collector moves during compaction operations. The fixup cache may provide predictive pointer update information during fixup operations for each object move within the heap.

Fixup cache tool for object memory compaction in an information handling system

An illustrative embodiment of a computer-implemented process for single pass marking of finalizable objects marks strong roots, marks finalizable roots and determines whether a strong work stack is empty. Responsive to a determination the strong work stack is empty the computer-implemented process determines whether a finalizable work stack is empty. Responsive to a determination the finalizable work stack is empty, synchronize threads, the computer-implemented process finalizes finalizable roots and merges mark maps to finish parallel marking.

Single pass marking of finalizable objects

A method for efficiently implementing a remembered set for a region-based garbage collector includes maintaining, for each region in an object heap, a remembered set card list (RSCL). Each card in the RSCL identifies an area in the object heap that includes at least one object that references an object in the region associated with the RSCL. The method further establishes a collection set identifying a subset of regions in the object heap on which to perform partial garbage collection. Prior to performing the partial garbage collection, the method flushes cards from RSCLs associated with the collection set to the card table, globally discards cards that are about to be rebuilt from all RSCLs, and globally cleans the card table. The method then adds cards to the RSCLs for inter-region references discovered while traversing live objects in the collection set. A corresponding computer program product and apparatus are also disclosed.

Efficient remembered set for region-based garbage collectors

A method for performing garbage collection on an object heap is described. In one embodiment, such a method includes performing a copy phase on an object heap by copying live objects from a source space to a destination space. An abort condition is generated when copying an object from the source space to the destination space fails due to insufficient space. In response to the abort condition, tracing work and reference updating associated with the copy phase are terminated. A mark phase is then initiated that marks live objects in the source space. This mark phase resumes tracing work and reference updating terminated by the copy phase in order to avoid or minimize the repetition of work performed by the copy phase. A corresponding computer program product and system are also described.

Copy collector with efficient abort-on-copy transition to mark collector

Illustrative embodiments provide a computer implemented method, an apparatus in the form of a data processing system and a computer program product for cache line reservations. In one embodiment, the computer implemented method comprises, dividing a memory into an unreserved section and a set of reserved sections. The method performs selected allocations of the memory only from the set of reserved sections, and performing un-selected allocations of the memory from the unreserved section. The method further mapping a specified selected allocation of the memory to a same corresponding line of cache memory each time the mapping for the specified selected allocation of the memory occurs, thereby maintaining locality.

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Unionville, Canada

Daryl James Maier