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DOI: 10.4230/LIPIcs.ECOOP.2021.17

Signal Classes: A Mechanism for Building Synchronous and Persistent Signal Networks

Authors: Tetsuo Kamina, Tomoyuki Aotani, and Hidehiko Masuhara

Published in: LIPIcs, Volume 194, 35th European Conference on Object-Oriented Programming (ECOOP 2021)

Abstract

Signals are principal abstraction in reactive programming languages and constitute the basics of reactive computations in modern systems, such as the Internet of Things. Signals sometimes utilize past values, which leads to space leak, a problem where accumulated past values waste resources such as the main memory. Persistent signals, an abstraction for time-varying values with their execution histories, provide a generalized and standardized way of space leak management by leaving this management to the database system. However, the current design of persistent signals is very rudimental. For example, they cannot represent complex data structures; they can only be connected using pre-defined API methods that implicitly synchronize the persistent signal network; and they cannot be created dynamically. In this paper, we show that these problems are derived from more fundamental one: no language mechanism is provided to group related persistent signals. To address this problem, we propose a new language mechanism signal classes. A signal class packages a network of related persistent signals that comprises a complex data structure. A signal class defines the scope of synchronization, making it possible to flexibly create persistent signal networks by methods not limited to the use of pre-defined API methods. Furthermore, a signal class can be instantiated, and this instance forms a unit of lifecycle management, which enables the dynamic creation of persistent signals. We formalize signal classes as a small core language where the computation is deliberately defined to interact with the underlying database system using relational algebra. Based on this formalization, we prove the language’s glitch freedom. We also formulate its type soundness by introducing an additional check of program well-formedness. This mechanism is implemented as a compiler and a runtime library that is based on a time-series database. The usefulness of the language is demonstrated through the vehicle tracking simulator and viewer case study. We also conducted a performance evaluation that confirms the feasibility of this case study.

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Tetsuo Kamina, Tomoyuki Aotani, and Hidehiko Masuhara. Signal Classes: A Mechanism for Building Synchronous and Persistent Signal Networks. In 35th European Conference on Object-Oriented Programming (ECOOP 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 194, pp. 17:1-17:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{kamina_et_al:LIPIcs.ECOOP.2021.17,
  author =	{Kamina, Tetsuo and Aotani, Tomoyuki and Masuhara, Hidehiko},
  title =	{{Signal Classes: A Mechanism for Building Synchronous and Persistent Signal Networks}},
  booktitle =	{35th European Conference on Object-Oriented Programming (ECOOP 2021)},
  pages =	{17:1--17:30},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-190-0},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{194},
  editor =	{M{\o}ller, Anders and Sridharan, Manu},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2021.17},
  URN =		{urn:nbn:de:0030-drops-140605},
  doi =		{10.4230/LIPIcs.ECOOP.2021.17},
  annote =	{Keywords: Persistent signals, Reactive programming, Time-series databases}
}

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DOI: 10.4230/LIPIcs.ECOOP.2018.2

ContextWorkflow: A Monadic DSL for Compensable and Interruptible Executions

Authors: Hiroaki Inoue, Tomoyuki Aotani, and Atsushi Igarashi

Published in: LIPIcs, Volume 109, 32nd European Conference on Object-Oriented Programming (ECOOP 2018)

Abstract

Context-aware applications, whose behavior reactively depends on the time-varying status of the surrounding environment - such as network connection, battery level, and sensors - are getting more and more pervasive and important. The term "context-awareness" usually suggests prompt reactions to context changes: as the context change signals that the current execution cannot be continued, the application should immediately abort its execution, possibly does some clean-up tasks, and suspend until the context allows it to restart. Interruptions, or asynchronous exceptions, are useful to achieve context-awareness. It is, however, difficult to program with interruptions in a compositional way in most programming languages because their support is too primitive, relying on synchronous exception handling mechanism such as try-catch. We propose a new domain-specific language ContextWorkflow for interruptible programs as a solution to the problem. A basic unit of an interruptible program is a workflow, i.e., a sequence of atomic computations accompanied with compensation actions. The uniqueness of ContextWorkflow is that, during its execution, a workflow keeps watching the context between atomic actions and decides if the computation should be continued, aborted, or suspended. Our contribution of this paper is as follows; (1) the design of a workflow-like language with asynchronous interruption, checkpointing, sub-workflows and suspension; (2) a formal semantics of the core language; (3) a monadic interpreter corresponding to the semantics; and (4) its concrete implementation as an embedded domain-specific language in Scala.

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Hiroaki Inoue, Tomoyuki Aotani, and Atsushi Igarashi. ContextWorkflow: A Monadic DSL for Compensable and Interruptible Executions. In 32nd European Conference on Object-Oriented Programming (ECOOP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 109, pp. 2:1-2:33, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{inoue_et_al:LIPIcs.ECOOP.2018.2,
  author =	{Inoue, Hiroaki and Aotani, Tomoyuki and Igarashi, Atsushi},
  title =	{{ContextWorkflow: A Monadic DSL for Compensable and Interruptible Executions}},
  booktitle =	{32nd European Conference on Object-Oriented Programming (ECOOP 2018)},
  pages =	{2:1--2:33},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-079-8},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{109},
  editor =	{Millstein, Todd},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2018.2},
  URN =		{urn:nbn:de:0030-drops-92074},
  doi =		{10.4230/LIPIcs.ECOOP.2018.2},
  annote =	{Keywords: workflow, asynchronous exception, checkpoint, monad, embedded domain specific language}
}

Document

DOI: 10.4230/DARTS.4.3.4

ContextWorkflow: A Monadic DSL for Compensable and Interruptible Executions (Artifact)

Authors: Hiroaki Inoue, Tomoyuki Aotani, and Atsushi Igarashi

Published in: DARTS, Volume 4, Issue 3, Special Issue of the 32nd European Conference on Object-Oriented Programming (ECOOP 2018)

Abstract

This artifact provides the Scala, Haskell, and Purescript implementations of ContextWorkflow, an embedded domain-specific language for interruptible and compensable executions, and demonstrates the maze search example described in the companion paper. The Haskell and Purescript implementations provide the core language constructs including \texttt{checkpoint} for partial aborts and \texttt{sub} for sub-workflows and show that ContextWorkflow can be embedded in eager and lazy languages as described in the companion paper. The Scala implementation does not only provide user-friendly syntax of ContextWorkflow but also gives the maze search example as an interactive GUI application.

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Hiroaki Inoue, Tomoyuki Aotani, and Atsushi Igarashi. ContextWorkflow: A Monadic DSL for Compensable and Interruptible Executions (Artifact). In Special Issue of the 32nd European Conference on Object-Oriented Programming (ECOOP 2018). Dagstuhl Artifacts Series (DARTS), Volume 4, Issue 3, pp. 4:1-4:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Article{inoue_et_al:DARTS.4.3.4,
  author =	{Inoue, Hiroaki and Aotani, Tomoyuki and Igarashi, Atsushi},
  title =	{{ContextWorkflow: A Monadic DSL for Compensable and Interruptible Executions (Artifact)}},
  pages =	{4:1--4:2},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2018},
  volume =	{4},
  number =	{3},
  editor =	{Inoue, Hiroaki and Aotani, Tomoyuki and Igarashi, Atsushi},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DARTS.4.3.4},
  URN =		{urn:nbn:de:0030-drops-92356},
  doi =		{10.4230/DARTS.4.3.4},
  annote =	{Keywords: workflow, asynchronous exception, checkpoint, monad, embedded domain specific language}
}

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Signal Classes: A Mechanism for Building Synchronous and Persistent Signal Networks

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ContextWorkflow: A Monadic DSL for Compensable and Interruptible Executions

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ContextWorkflow: A Monadic DSL for Compensable and Interruptible Executions (Artifact)

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