Deterministic Thread Replay via Timestamped Instruction Recording
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Solution Overview
Problem
Conventional debugging interfaces fail to accurately record and replay the execution of programs with multiple threads, leading to inconsistencies in the replay process due to varying thread scheduling across different operating systems and execution runs.
Innovation Solution
An execution recorder that uses thread identifiers and timestamps to record and replay the instructions executed by a program, ensuring deterministic playback by correlating executed instructions with their corresponding source code statements and data values, and providing a data provider service to maintain accurate data values during playback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional debugging interfaces record executed instructions without thread identifiers and timestamps, then the recording process is simple, but the replay process becomes inconsistent across different operating systems and execution runs
Solution Approach 1:
The patent segments the recording structure into distinct components: instruction identifiers, thread identifiers, and timestamps. Each executed instruction is broken down into these discrete elements that can be independently recorded and later reconstructed during playback, ensuring consistent reproduction across different environments.
Solution Approach 2:
The patent applies preliminary action by recording thread identifiers and timestamps at the moment of instruction execution. This advance capture of contextual information ensures that when playback occurs, the complete execution context is already available, eliminating the need for complex runtime thread scheduling analysis and ensuring consistent replay.
2Adaptability or versatility
If thread scheduling is allowed to vary across operating systems for flexibility, then system adaptability is improved, but debugging replay accuracy deteriorates
Solution Approach 1:
The patent creates a precise copy of the execution timeline by recording timestamps for each instruction execution. This timestamped record serves as an immutable reference that accurately captures the original execution order, allowing debugging tools to replay instructions in the exact sequence they occurred, regardless of how thread scheduling varies across different operating systems.
Solution Approach 2:
The patent adds the time dimension to instruction recording by incorporating timestamps. This transforms the recording from a simple instruction sequence into a time-ordered execution trace, enabling accurate replay by restoring instructions in their original temporal sequence rather than relying on thread scheduling behavior.
3Measurement precision
If thread identifiers are recorded for each executed instruction, then replay accuracy is improved, but the amount of recorded data increases
Solution Approach 1:
The patent makes the thread identifier field multi-functional: it serves both to identify the executing thread and to implicitly capture scheduling information. This universal approach allows the same data structure to provide multiple pieces of information without requiring separate fields, thereby improving execution trace accuracy while minimizing data volume increase.
Data Source
AI summary
A computer system receives a first instruction identifier identifying a first instruction being executed by a first thread associated with a first virtual machine and receives a second instruction identifier identifying a second instruction being executed by a second thread associated with the first virtual machine. The system produces an execution record comprising the first instruction identifier, a first thread identifier identifying the first thread, a first timestamp reflecting a first real-time clock value associated with executing the first instruction, the second instruction identifier, a second thread identifier identifying the second thread, and a second timestamp reflecting a second real-time clock value associated with executing the second instruction. The system executes the first instruction by a first replay thread of a second virtual machine and the second instruction by a second replay thread of the second virtual machine in a chronological order specified by the first timestamp and the second timestamp.