SHF: Small: Specifying and Verifying Essential Deterministic Behavior of Concurrent Programs

并行多线程程序比它们的顺序程序更难编写，因为在编写并行程序时，程序员除了考虑程序的算法正确性外，还必须考虑由于线程交错而导致的所有可能的行为。一个普遍的信念是，使大量程序员能够访问多线程编程的唯一方法是提出编程范例和相关工具，明确地将关于函数正确性的推理与关于由并行引起的额外行为的推理分开。该项目研究将程序的并行化正确性方面与其函数正确性分离的策略。首先，对于大多数并行程序来说，希望由并行程序中的线程调度器引入的不确定性不会改变程序的预期输出。这个项目将开发一个断言框架，用于指定并行程序的区域在非确定性线程交织的情况下具有确定性的行为。第二种策略基于这样的观察，即并行程序开发的一个自然步骤是首先使用受控的非确定性扩展顺序算法，然后在线程交织引入额外的不确定性时进行实际的并行化。这个项目将研究非确定性顺序程序作为一种规范机制的使用，使得对于并行程序的每次执行，存在对应的非确定性顺序程序的等价执行。这种不确定的顺序程序将并行化正确性与功能正确性解耦。

Parallel multi-threaded programs are more difficult to write than their sequential counterparts because while writing parallel programs programmers must consider all possible behaviors due to thread interleavings, in addition to the algorithmic correctness of the program. A widespread belief is that the only way to make multi-threaded programming accessible to a large number of programmers is to come up with programming paradigms and associated tools that explicitly separate reasoning about functional correctness from reasoning about additional behaviors arising due to parallelism.This project investigates strategies for separating the parallelization correctness aspect of a program from its functional correctness. First, for most parallel programs it is desired that the non-determinism introduced by the thread scheduler in a parallel program does not change the intended output of the program. This project will develop an assertion framework for specifying that regions of a parallel program behave deterministically despite non-deterministic thread interleaving.The second strategy is based on the observation that a natural step in the development of a parallel program is to first extend the sequential algorithm with a controlled amount of non-determinism, followed by the actual parallelization, when additional non-determinism is introduced by thread interleavings. This project will investigate the use of non-deterministic sequential programs as a specification mechanism, such that for each execution of a parallel program there exists an equivalent execution of the corresponding non-deterministic sequential program. Such non-deterministic sequential programs decouple parallelization correctness from functional correctness.