Abstract
We present a denotational semantics for weak memory concurrency that avoids thin-air reads, provides data-race free programs with sequentially consistent semantics (DRF-SC), and supports a compositional refinement relation for validating optimisations. Our semantics identifies false program dependencies that might be removed by compiler optimisation, and leaves in place just the dependencies necessary to rule out thin-air reads. We show that our dependency calculation can be used to rule out thin-air reads in any axiomatic concurrency model, in particular C++. We present a tool that automatically evaluates litmus tests, show that we can augment C++ to fix the thin-air problem, and we prove that our augmentation is compatible with the previously used compilation mappings over key processor architectures. We argue that our dependency calculation offers a practical route to fixing the longstanding problem of thin-air reads in the C++ specification.
Keywords
- Thin-air problem
- Weak memory concurrency
- Compiler Optimisations
- Denotational Semantics
- Compositionality
This work was funded by EPSRC Grants EP/M017176/1, EP/R020566/1 and EP/S028129/1, the Lloyds Register Foundation, and the Royal Academy of Engineering.
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Paviotti, M., Cooksey, S., Paradis, A., Wright, D., Owens, S., Batty, M. (2020). Modular Relaxed Dependencies in Weak Memory Concurrency. In: Müller, P. (eds) Programming Languages and Systems. ESOP 2020. Lecture Notes in Computer Science(), vol 12075. Springer, Cham. https://doi.org/10.1007/978-3-030-44914-8_22
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