Thread Local Storage Update Buffer Queuing for Low Contention
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Solution Overview
Problem
In computer systems, especially those with a small number of application threads, garbage collection methods face contention issues when accessing update buffers, leading to increased latency and reduced scalability due to the need for atomic operations on a global queue, which affects the efficiency of both application and garbage collector threads.
Innovation Solution
Implementing a method where each mutator thread uses two slots in Thread Local Storage (TLS) for a current and finished update buffer pointer, allowing the garbage collector thread to periodically check for available buffers and reduce contention by minimizing access to the global queue, thus optimizing latency for application threads at the expense of potentially increased latency for garbage collector threads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a global queue is used for update buffers with atomic operations, then garbage collection can be implemented, but contention increases and scalability decreases
Solution Approach 1:
The patent divides the single global queue into multiple per-thread update buffers, with each thread having its own dedicated buffer. This segmentation eliminates the need for atomic operations on a shared queue, as threads operate on their own buffers independently, thereby reducing contention and improving scalability while maintaining garbage collection functionality.
Solution Approach 2:
The patent extracts the contentious atomic operation mechanism from the update buffer management process. By removing the global queue and its associated lock/CAS operations, the system eliminates the bottleneck that limited scalability, while still enabling garbage collection through alternative buffer management approaches.
2Reliability
If atomic operations are used for queue access, then thread safety is ensured, but latency increases due to synchronization overhead
Solution Approach 1:
By assigning dedicated update buffers to individual threads, the patent eliminates the need for atomic operations and synchronization primitives. Each thread safely writes to its own buffer without contention, achieving both thread safety and reduced latency simultaneously.
3Productivity
If update buffers are frequently added to global queue, then garbage collection efficiency improves, but memory resource contention increases
Solution Approach 1:
The patent segments the monolithic global queue into thread-specific update buffers, allowing garbage collector threads to access buffers without contention. GC threads can efficiently process update buffers from multiple application threads by reading from their respective buffers directly, eliminating memory resource contention while maintaining GC efficiency.
Data Source
AI summary
A method for queuing update buffers to enhance garbage collection. The method includes running an application thread and providing, for the application thread, a data structure including current and finished update buffer slots. The method includes providing an update buffer for the application thread and storing a pointer to the update buffer in the current update buffer slot. The method includes storing null in the finished update buffer slot and, with the application thread, writing to the update buffer. The thread may write a pointer to the filled update buffer in the finished update buffer slot after the buffer is filled. The method includes using a garbage collector thread to inspect the finished update buffer slot and claim filled buffers and change the pointer to null. The thread then obtains an empty update buffer and updates the current update buffer slot to point to the new buffer.