Multi-threaded Shared Memory Concurrency via Phase Segmentation
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Solution Overview
Problem
In multithreaded environments, shared memory can lead to incomplete or corrupt data due to one thread reading while another is writing, necessitating protection of shared resources to ensure atomic updates across threads.
Innovation Solution
Implementing a method that allows all threads access to data during the initial phases of a write operation, blocking only during the commit phase to reduce cross-thread interference and prevent partial write results from being accessed, thereby ensuring atomicity and higher concurrency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional locking mechanisms are used to protect shared memory, then data integrity is maintained, but thread concurrency is reduced due to blocking during entire write operations
Solution Approach 1:
The write operation is segmented into three distinct phases: (1) a non-blocking phase where readers can access data while the writer prepares updates, (2) a commit phase where the writer atomically publishes results, and (3) a cleanup phase. This segmentation allows readers and writers to operate concurrently in different phases, improving thread concurrency while maintaining data integrity through the atomic commit mechanism.
Solution Approach 2:
The writer performs all data preparation and computation work in advance during the non-blocking phase, before other threads need to access the updated data. This preliminary action allows the actual memory update to be completed atomically and quickly, reducing the blocking time for other threads while ensuring data integrity.
2Reliability
If blocking is applied during entire write operations, then partial write results are prevented from being accessed, but cross-thread interference increases
Solution Approach 1:
The write operation is divided into phases with different blocking characteristics. During the preparation phase, no blocking occurs allowing maximum concurrency. During the commit phase, brief blocking is applied only when necessary to ensure atomicity. This segmented approach minimizes cross-thread interference while maintaining atomic update guarantees.
Solution Approach 2:
A write barrier or memory fence acts as an intermediary mechanism that coordinates between writers and readers. It provides a controlled point where blocking occurs to ensure atomicity, while allowing non-blocking access during other phases. This intermediary reduces overall cross-thread interference by concentrating synchronization only where absolutely necessary.
3Reliability
If full blocking is used during write operations, then data corruption is prevented, but system performance decreases due to reduced concurrency
Solution Approach 1:
The write operation is segmented into phases where blocking is applied only during the critical commit phase rather than throughout the entire operation. This allows the majority of the write work to proceed without blocking other threads, improving system performance while maintaining data consistency through the atomic commit mechanism.
Solution Approach 2:
All data preparation and validation is performed in advance during the non-blocking phase. This preliminary action ensures that when the commit phase occurs, only a brief blocking period is needed to publish the pre-validated data atomically, thereby maintaining data consistency while minimizing performance impact.
Data Source
AI summary
Aspects of the present invention comprise systems and methods for protecting multi-threaded access to shared memory. Some aspects provide higher data concurrency than other methods. Some aspects relate to methods and systems that provide access to data for all threads during the first phases of one thread's write operation. Some aspects provide all threads access to a particular data unit until one thread enters the commit phase of the write operation. Some aspects manage a computing data resource such that, when a thread enters the commit phase, all pending read requests are fulfilled, all pending write requests are allowed to proceed to commit phase at which point they are blocked, all new read and write requests are blocked and the commit phase is completed by updating the target data and releasing the blocked requests.Some aspects provide improved concurrency by performing reduced cross-thread interference. Some aspects may be implemented at any level from hardware to high-level languages. Some aspects protect readers from accessing partial write results which avoids retry semantics and data corruption.