Sanchari Sil | Searcharxiv

arXiv2026

Verifying Sequential Consistency under Bounded Preemptions

Gibbons and Korach studied a fundamental problem in 1997: given an observed sequence of reads and writes of a multi-threaded program, does there exist an interleaving which is sequentially consistent? Apart from applications in testing shared memory implementations, a procedure for this problem is employed in Dynamic Partial-Order-Reduction (DPOR) algorithms. The problem is known to be NP-hard even when different syntactic parameters are kept bounded. In this paper, we consider a restriction on the kind of interleaving required: does there exist a sequentially-consistent interleaving with at most {\pi} preemptions? Empirical evidence suggests that several bugs manifest within a few preemptive switches. This motivates us to investigate the problem under bounded preemptions. Our results exhibit a trichotomy: the problem lends to a polynomial-time algorithm for the class of single-writer programs where for each variable, there is a single thread writing to it; it becomes NP-hard for two-writer programs and finally, for three-writer programs, we get a conditional lower bound under the Exponential-Time-Hypothesis. When the number of preemptions {\pi} is not bounded, we show the problem to be W[1]-hard, and hence unlikely to be fixed-parameter-tractable with parameter {\pi}.

cs.PL↗

arXiv2026

Complexity of Consistency Testing for the Release-Acquire Semantics

In a seminal work, Gibbons and Korach studied the complexity of deciding whether an observed sequence of reads and writes of a multi-threaded program admits a sequentially consistent interleaving. They showed the problem to be NP-hard even under strong syntactic restrictions. More recently, Chakraborty et al. considered the problem for weak memory models and proved that NP-hardness remains even when the number of threads, the number of memory locations, and the value domain are all bounded. In this paper we revisit the problem for the release-acquire variants of the C11 memory model. Our main positive result is that consistency testing can be done in polynomial-time when each memory location is written by at most one thread (multiple readers are allowed). Notably, this restriction is already NP-hard for sequential consistency. We complement this upper bound with tight hardness results: the problem is NP-hard when two threads may write to the same location, and allowing three writers per location rules out 2^{o(k)}.n^{O(1)} algorithms under the Exponential Time Hypothesis, where k denotes the number of threads, and n the number of memory operations.

cs.CC↗

arXiv2023

TSO Games -- On the decidability of safety games under the total store order semantics

We consider an extension of the classical Total Store Order (TSO) semantics by expanding it to turn-based 2-player safety games. During her turn, a player can select any of the communicating processes and perform its next transition. We consider different formulations of the safety game problem depending on whether one player or both of them transfer messages from the process buffers to the shared memory. We give the complete decidability picture for all the possible alternatives.

cs.GT↗

arXiv2023

TSO Games -- On the decidability of safety games under the total store order semantics (extended LMCS version with appendix)

We consider an extension of the classical Total Store Order (TSO) semantics by expanding it to turn-based 2-player safety games. During her turn, a player can select any of the communicating processes and perform its next transition. We consider different formulations of the safety game problem depending on whether one player or both of them transfer messages from the process buffers to the shared memory. We give the complete decidability picture for all the possible alternatives.

cs.GT↗