Concurrent Refinement Threads for Garbage Collector Delays

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional garbage collection techniques, such as generational and space-incremental methods, cause significant delays due to the need to suspend non-collection threads during the scanning and updating of large remembered sets, which are essential for updating references in memory reclamation processes, especially in real-time or interactive systems.

Innovation Solution

Implementing refinement threads to manage and update remembered sets concurrently with non-collection threads, sequestering them before the main scanning phase to prevent further changes, and using collection set levels to prioritize and index reference location lists for efficient processing, thereby reducing the time required for scanning and updating.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional garbage collection techniques are used to scan and update remembered sets, then memory reclamation can be performed, but non-collection threads must be suspended causing significant delays

Engineering Contradiction:

Improvememory reclamation accuracyVSAvoidsystem operation delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The remembered set is divided into multiple segments that can be processed independently and concurrently. Different segments are scanned and updated by different threads simultaneously, allowing the garbage collection process to proceed without suspending all non-collection threads, thus reducing system operation delays while maintaining reclamation accuracy.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The remembered set is sequestered (marked for collection) before the main scanning phase begins. This preliminary action allows refinement threads to concurrently scan and update the remembered set segments without interference from ongoing allocations, enabling parallel processing and reducing the time threads are suspended.

Inventive Principle:

Principle #10Preliminary action

2Manufacturing precision

If the entire remembered set is scanned and updated sequentially, then all references can be accurately updated, but the processing time increases significantly

Engineering Contradiction:

Improvereference update accuracyVSAvoidprocessing speed

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Multiple refinement threads are merged to work together on different segments of the remembered set simultaneously. These threads coordinate their efforts to scan, update, and consolidate reference information across all segments, achieving both high processing speed through parallelism and high accuracy through coordinated validation.

Inventive Principle:

Principle #5Merging (Combining)

3Loss of time

If refinement threads are used to concurrently process remembered sets, then processing time is reduced, but system complexity increases

Engineering Contradiction:

Improvescanning and updating timeVSAvoidthread coordination complexity

Core Design Contradiction:

Loss of timeVSDevice complexity

Solution Approach 1:

A sequestration mechanism acts as an intermediary between the refinement threads and the main garbage collection process. This mediator coordinates the concurrent operations by managing the sequestration state of remembered sets, controlling when threads can access and modify data, and ensuring that all threads complete their work before the collection phase begins, thus reducing the perceived complexity of thread coordination.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Stability of the object's composition

If non-collection threads are suspended during remembered set processing, then consistency is maintained, but system responsiveness decreases

Engineering Contradiction:

Improvememory structure consistencyVSAvoidsystem responsiveness

Core Design Contradiction:

Stability of the object's compositionVSSpeed

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Non-collection threads continue to execute their useful work concurrently with the refinement threads processing the remembered set. The system maintains continuous operation rather than suspending threads, with the sequestration mechanism ensuring that consistency is preserved even during concurrent access, thus maintaining system responsiveness.

Inventive Principle:

Principle #20Continuity of useful action

Data Source

PatentUS7650350B1Method and apparatus for concurrently processing remembered sets in a space-incremental garbage collector

Publication Date: 2010.01.19 ORACLE AMERICAN INC

AI summary

In a space incremental garbage collector, delays caused by scanning remembered sets are reduced by scanning the remembered sets mostly concurrently with the operation of the non-collection threads. Before scanning, remembered sets associated with regions in some collection set are “sequestered” (no further insertions are allowed by the non-collection threads or the collector) in order to prevent further changes. Any further changes to these sequestered remembered sets that occur before phase two of the scanning process are then handled by one or more “refinement threads.” Each refinement thread is a thread that can record reference locations in remembered sets, scan entries in collection set remembered sets and update reference location lists for use in the aforementioned second phase of remembered set processing. The refinement threads operate concurrently with the operation of the non-collection threads.