Concurrent Garbage Collection Single Heap Traversal
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Solution Overview
Problem
Conventional garbage collection methods require multiple traversals of the heap, leading to time and resource inefficiencies, as well as prolonged pause times for application threads, due to their phased approach which increases memory accesses and pollutes caches.
Innovation Solution
Implementing a concurrent garbage collection method that combines the identification, marking, copying, and re-referencing of live objects in a single traversal, utilizing past liveness information to select evacuation regions and leveraging multiple CPU threads for parallel processing, thereby reducing the number of memory accesses and pause times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple traversals of the heap are performed in conventional garbage collection, then thorough identification of live objects is achieved, but time consumption and resource usage increase significantly
Solution Approach 1:
The patent applies preliminary action by using liveness information obtained from a prior garbage collection cycle to pre-select the evacuation region before the current garbage collection cycle begins. This allows the garbage collector to skip the traversal step and directly evacuate objects to the predetermined region, significantly reducing the time required while maintaining reliability through the use of previously validated liveness data
Solution Approach 2:
The patent merges multiple garbage collection phases (identification, marking, copying, and re-referencing of live objects) into a single traversal of the heap. By combining these traditionally separate phases into one concurrent operation, the patent reduces the number of traversals from multiple to one, thereby decreasing garbage collection time while maintaining thoroughness through coordinated concurrent execution
2Reliability
If multiple traversals of the heap are performed in conventional garbage collection, then complete garbage collection is achieved, but the number of memory accesses increases and caches are polluted
Solution Approach 1:
The patent uses preliminary action by determining the evacuation region in advance based on liveness information from a prior garbage collection cycle. This pre-determination eliminates the need for multiple traversals to identify where objects should be evacuated, reducing memory accesses and preventing cache pollution while maintaining complete garbage collection through the single optimized traversal
Solution Approach 2:
The patent combines identification, marking, copying, and re-referencing operations into a single traversal phase that executes concurrently with application threads. This merging eliminates redundant memory accesses that would occur in separate traversal phases, improving memory access efficiency and reducing cache pollution while ensuring complete garbage collection through coordinated concurrent execution
3Device complexity
If phased garbage collection approach is used, then systematic processing of live objects is achieved, but pause times for application threads are prolonged
Solution Approach 1:
The patent applies continuity of useful action by executing the garbage collection phase concurrently with application threads rather than requiring application threads to pause. The single traversal approach with pre-determined evacuation regions allows garbage collection to proceed continuously alongside application execution, eliminating prolonged pause times while maintaining systematic processing through coordinated concurrent operations
Solution Approach 2:
The patent uses preliminary action to pre-select evacuation regions based on prior liveness information, which enables the garbage collection phase to execute concurrently with application threads. This preliminary preparation eliminates the need to pause application threads during region selection and object identification, allowing continuous useful action while maintaining systematic processing of live objects
Data Source
AI summary
Systems and techniques for garbage collection are disclosed for concurrently performing a garbage collection cycle in a single traversal of a garbage collection heap while application threads are running. The garbage collection cycle includes marking a first memory object as live. The garbage collection cycle also includes determining that a forwarding pointer of the first memory object points to the first memory object. The garbage collection cycle further includes evacuating the first memory object to a free region based on the determining. The garbage collection cycle additionally includes evacuating a second memory object in the same single traversal of the garbage collection heap in which the first memory object is being marked live.