InstantCheck: Checking the Determinism of Parallel Programs Using On-the-Fly Incremental Hashing

Abstract

Developing multithreaded programs in shared-memory systems is difficult. One key reason is the nondeterminism of thread interaction, which may result in one code input producing different outputs in different runs. Unfortunately, enforcing determinism by construction typically comes at a performance, hardware, or programmability cost. An alternative is to check during testing whether code is deterministic.This paper presents InstantCheck, a novel technique that checks determinism with a very small runtime overhead while requiring only a minor hardware extension. During code testing, InstantCheck can check whether the code under test ends up in a deterministic state in various runs. The idea is to compute a 64-bit hash of the memory state and compare the hashes of different test runs that have the same input. If two runs have different hashes, InstantCheck reports state nondeterminism. For efficient operation, InstantCheck uses on-the-fly incremental hashing in hardware. The hash is kept in a per-core 64-bit register, which trivially supports virtualization, migration, and context switching.We use InstantCheck to understand the determinism properties of 17 popular applications, including Sphinx3, PBZip2, PARSEC, and SPLASH-2. InstantCheck incurs a negligible average runtime overhead of 0.3% over native testing runs. We also show how using InstantCheck programmers can find bugs and discuss other applications of fast memory-state hashing. While using InstantCheck, we found a real bug in the widely used PARSEC benchmark.

Axis: Automatically fixing atomicity violations through solving control constraints

“…They still face many challenges such as high runtime overhead or extra manual annotations. An alternative approach, checking the determinism through the testing [24], complements our approach as it can be used to filter out the benign violations.…”

BulkCompactor: Optimized deterministic execution via Conflict-Aware commit of atomic blocks

“…Stream-based programming languages such as StreamIt [25] provide determinism as the deterministic message channel handles all the communication. Finally, some works check if a program behaves deterministically in a nondeterministic execution environment (e.g., [7,8,20]). …”

Fence Placement for Legacy Data-Race-Free Programs via Synchronization Read Detection

“…We use the term Pensieve throughout this section to refer to the version presented inFang et al [2003] with locally optimized fence minimization, rather than the laterSura et al [2005].6 Although the lock-free programs use user-defined synchronization exclusively, the SPLASH-2 programs make use of user-defined synchronization (in programs such as FMM[Tian et al 2008] and Volrend[Nistor et al 2010]) and also employ library calls to locks and barriers.…”