Data Race Analysis via Memory Value Substitution in Time-Travel Debugging

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Solution Overview

Problem

Identifying and debugging data races in multi-threaded applications is challenging due to their rarity, unreliability, and difficulty in reproduction, especially when conventional diagnostic tools operate on live forward-executing code.

Innovation Solution

Leveraging historic debugging technologies to substitute memory values during replayed execution, allowing for simulation of data races and their corrections, enabling analysis of potential effects on function behavior without requiring actual occurrence during tracing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional diagnostic tools are used to identify data races in multi-threaded applications, then developers can observe code execution behaviors in real-time, but data races are difficult to reproduce and identify due to their rarity and timing-dependent nature

Engineering Contradiction:

Improvereliability of data race reproductionVSAvoidtime to identify and fix data races

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system performs preliminary tracing and recording of thread execution during normal application operation, capturing detailed state information before data race analysis is attempted. This preliminary action stores execution history that can be later analyzed without requiring reproduction of the original timing conditions, thereby resolving the contradiction between unreliable reproduction and identification time

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system creates a copy of the traced execution history and thread states, allowing analysis of past execution patterns without needing to reproduce the exact timing conditions. By working with copied trace data rather than live execution, the system can reliably identify data races that would otherwise be difficult to reproduce, addressing both the reliability and time consumption issues

Inventive Principle:

Principle #26Copying

2Measurement precision

If developers use unit testing and code review to identify data races, then they can examine code logic, but the timing-dependent nature of data races makes them unreliable to reproduce

Engineering Contradiction:

Improveprecision of data race detectionVSAvoidreliability of data race occurrence

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The system implements feedback by comparing traced execution patterns against expected synchronization protocols. When inconsistencies are detected in the traced data, the system generates notifications to developers. This feedback mechanism provides precise detection of data races based on actual execution history rather than relying on reproduction, resolving the contradiction between detection precision and occurrence reliability

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs preliminary tracing of thread execution and synchronization operations, capturing detailed state information before analysis. This preliminary recording of execution history enables precise detection of data races by analyzing actual timing and ordering of operations, without requiring the races to be reliably reproduced during analysis

Inventive Principle:

Principle #10Preliminary action

3Difficulty of detecting and measuring

If developers manually trace through code execution to identify data races, then they can observe thread interleaving, but the process is extremely time-consuming and difficult

Engineering Contradiction:

Improvedifficulty of identifying data race root causesVSAvoidtime to determine root cause of undesired behavior

Core Design Contradiction:

Difficulty of detecting and measuringVSLoss of time

Solution Approach 1:

The system performs self-service by automatically analyzing traced execution data to identify data races and generate notifications. Instead of requiring developers to manually trace through code execution and thread interleaving, the system autonomously processes the traced data, identifies synchronization issues, and presents findings to developers. This automation dramatically reduces both the difficulty and time required to identify data race root causes

Inventive Principle:

Principle #25Self-service

Data Source

PatentEP4014119B1Data race analysis based on altering function internal loads during time-travel debugging

Publication Date: 2024.06.05 MICROSOFT TECHNOLOGY LICENSING LLC

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AI summary

Determining whether a function-internal load modification affects the output of a traced function. A function is identified within a traced portion of a prior execution of an entity. The function comprises a sequence of executable instructions and produces one or more outputs. Traced output data value(s) that were produced by the traced instance of the function are determined, and an executable instruction within the sequence of executable instructions that performs a load from memory is identified. Execution of the function is emulated, while substituting a traced memory value loaded by the executable instruction during the traced instance of the function with a different memory value, and while producing emulated output data values(s). Based on there being a difference between the traced output data values(s) and the emulated output data values(s), a notification is generated at a user interface or to a software component.