Concurrent Young Generation Evacuation for Real-Time Garbage Collection
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Solution Overview
Problem
Generational garbage collectors cause user-perceived pauses due to the 'stop the world' nature of garbage collection, which is detrimental in applications requiring real-time response, as they halt the mutator during the collection cycle.
Innovation Solution
Divide the young generation into two young generations, allowing concurrent evacuation of one while allocating the other, and subsequently exchanging their roles, with a filtering write barrier to manage references, thereby minimizing pause times by allowing the mutator to continue executing throughout the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If garbage collection is performed in a stop the world fashion, then the garbage collection process can complete thoroughly, but user perceived pauses increase
Solution Approach 1:
The young generation is divided into two separate young generations (young generation 1 and young generation 2), allowing the garbage collector to evacuate one while the mutator allocates to the other. This segmentation enables concurrent operation and reduces the impact of stop-the-world pauses by distributing the collection workload across multiple generations.
2Reliability
If the mutator is halted during the collection cycle, then the garbage collection can be performed accurately, but application responsiveness deteriorates
Solution Approach 1:
The mutator continues to execute and allocate objects to the second young generation concurrently while the garbage collector evacuates the first young generation. This continuous operation maintains application responsiveness and throughput while the garbage collection process proceeds in the background without halting the mutator.
3Productivity
If garbage collection is performed frequently on the young generation, then memory space is reclaimed quickly, but the complexity of the collection policy increases
Solution Approach 1:
The system dynamically switches between evacuating young generation 1 and young generation 2 based on their respective states. When one young generation is fully evacuated, the system transitions to evacuating the other, creating a dynamic collection policy that adapts to the current state of memory allocation and reduces overall complexity.
Data Source
AI summary
The invention relates to a method for performing generational garbage collection on a heap comprising a plurality of generations. The method involves dividing a young generation of the heap into a first young generation and a second young generation, evacuating the first young generation concurrently with allocating the second young generation, and evacuating the second young generation concurrently with allocating the first young generation and subsequent to fully evacuating the first young generation.