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Session types using affinity and exception handling mechanisms have been developed to ensure the communication safety of protocols implemented in concurrent and distributed programming languages. Nevertheless, current affine session types are inadequate for specifying real-world asynchronous protocols, as they are usually imposed by time constraints which enable timeout exceptions to prevent indefinite blocking while awaiting valid messages. This paper proposes the first formal integration of affinity, time constraints, timeouts, and time-failure handling based on multiparty session types for supporting reliability in asynchronous distributed systems. With this theory, we statically guarantee that asynchronous timed communication is deadlock-free, communication safe, while being fearless -- never hindered by timeout errors or abrupt terminations. To implement our theory, we introduce a Rust toolchain designed to facilitate the implementation of safe affine timed protocols. Our toolchain leverages generic types and the time library to handle timed communications, integrated with optional types for affinity. We evaluate our approach by extending diverse examples from the literature to incorporate time and timeouts, demonstrating that our solution incurs negligible overhead compared with an untimed implementation. We also showcase the correctness by construction of our approach by implementing various real-world use cases, including a remote data protocol from the Internet of Remote Things domain, as well as protocols from real-time systems like Android motion sensors and smartwatches., Comment: ECOOP 2024

Multiparty session types (MPST) provide a type discipline where a programmer or architect specifies a whole view of communications as a global protocol, and each distributed program is locally type-checked against its end-point projection. After 10 years from the birth of MPST, Scalas and Yoshida discovered that the proofs of type safety in the literature which use the end-point projection with mergeability are flawed. After this paper, researchers wrongly believed that the end-point projection (with mergeability) was unsound. We correct this misunderstanding, proposing a new general proof technique for type soundness of multiparty session $\pi$-calculus, which uses an association relation between a global type and its end-point projection.

Session types provide a typing discipline for message-passing systems. However, their theory often assumes an ideal world: one in which everything is reliable and without failures. Yet this is in stark contrast with distributed systems in the real world. To address this limitation, we introduce a new asynchronous multiparty session types (MPST) theory with crash-stop failures, where processes may crash arbitrarily and cease to interact after crashing. We augment asynchronous MPST and processes with crash handling branches, and integrate crash-stop failure semantics into types and processes. Our approach requires no user-level syntax extensions for global types, and features a formalisation of global semantics, which captures complex behaviours induced by crashed/crash handling processes. Our new theory covers the entire spectrum, ranging from the ideal world of total reliability to entirely unreliable scenarios where any process may crash, using optional reliability assumptions. Under these assumptions, we demonstrate the sound and complete correspondence between global and local type semantics, which guarantee deadlock-freedom, protocol conformance, and liveness of well-typed processes by construction, even in the presence of crashes., Comment: arXiv admin note: substantial text overlap with arXiv:2305.06238

A dataset of 3D-GRE and 3D-TSE brain 3T post contrast T1-weighted images as part of a quality improvement project were collected and shown to five neuro-radiologists who evaluated each sequence for both image quality and imaging artifacts. The same scans were processed using the MRQy tool for objective, quantitative image quality metrics. Using the combined radiologist and quantitative metrics dataset, a decision tree classifier with a bagging ensemble approach was trained to predict radiologist assessment using the quantitative metrics. A machine learning model was developed for the following three tasks: (1) determine the best model / performance for each MRI sequence and evaluation metric, (2) determine the best model / performance across all MRI sequences for each evaluation metric, and (3) determine the best general model / performance across all MRI sequences and evaluations. Model performance for imaging artifact was slightly higher than image quality, for example, the final generalized model AUROC for image quality was 0.77 (0.41 - 0.84, 95% CI) while imaging artifact was 0.78 (0.60 - 0.93, 95% CI). Further, it was noted that the generalized model performed slightly better than the individual models (AUROC 0.69 for 3D-GRE image quality, for example), indicating the value in comprehensive training data for these applications. These models could be deployed in the clinic as automatic checks for real-time image acquisition to prevent patient re-scanning requiring another appointment after retrospective radiologist analysis or improve reader confidence in the study. Further work needs to be done to validate the model described here on an external dataset. The results presented here suggest that MRQy could be used as a foundation for quantitative metrics as a surrogate for radiologist assessment.

Session types provide a typing discipline for message-passing systems. However, most session type approaches assume an ideal world: one in which everything is reliable and without failures. Yet this is in stark contrast with distributed systems in the real world. To address this limitation, we introduce Teatrino, a code generation toolchain that utilises asynchronous multiparty session types (MPST) with crash-stop semantics to support failure handling protocols. We augment asynchronous MPST and processes with crash handling branches. Our approach requires no user-level syntax extensions for global types and features a formalisation of global semantics, which captures complex behaviours induced by crashed/crash handling processes. The sound and complete correspondence between global and local type semantics guarantees deadlock-freedom, protocol conformance, and liveness of typed processes in the presence of crashes. Our theory is implemented in the toolchain Teatrino, which provides correctness by construction. Teatrino extends the Scribble multiparty protocol language to generate protocol-conforming Scala code, using the Effpi concurrent programming library. We extend both Scribble and Effpi to support crash-stop behaviour. We demonstrate the feasibility of our methodology and evaluate Teatrino with examples extended from both session type and distributed systems literature., Comment: ECOOP 2023