top/int.tex

   1 \documentclass[../thesis.tex]{subfiles}
   2
   3 \input{subfilepreamble}
   4
   5 \begin{document}
   6 \input{subfileprefix}
   7
   8 \chapter{Integration with \texorpdfstring{\gls{ITASK}}{iTask}}%
   9 \label{chp:integration_with_itask}
  10 \begin{chapterabstract}
  11         \noindent This chapter shows the integration of \gls{MTASK} with \gls{ITASK} by showing:
  12         \begin{itemize}
  13                 \item an architectural overview \gls{MTASK} applications;
  14                 \item on the interface for connecting devices;
  15                 \item the interface for lifting \gls{MTASK} tasks to \gls{ITASK} tasks;
  16                 \item a interface for lifting \gls{ITASK} \glspl{SDS} to \gls{MTASK} \glspl{SDS};
  17                 \item and finishes with non-trivial home automation example application using all integration mechanisms;
  18         \end{itemize}
  19 \end{chapterabstract}
  20
  21 The \gls{MTASK} language is a multi-view \gls{DSL}, i.e.\ there are multiple interpretations possible for a single \gls{MTASK} term.
  22 Using the byte code compiler (\cleaninline{BCInterpret}) \gls{DSL} interpretation, \gls{MTASK} tasks can be fully integrated in \gls{ITASK}.
  23 They are executed as if they are regular \gls{ITASK} tasks and they communicate may access \glspl{SDS} from \gls{ITASK} as well.
  24 \Gls{MTASK} devices contain a domain-specific \gls{OS} and are little \gls{TOP} engines in their own respect, being able to execute tasks.
  25 \Cref{fig:mtask_integration} shows the architectural layout of a typical \gls{IOT} system created with \gls{ITASK} and \gls{MTASK}.
  26 The entire system is written as a single \gls{CLEAN} specification where multiple tasks are executed at the same time.
  27 Tasks can access \glspl{SDS} according to many-to-many communication and multiple clients can work on the same task.
  28 Devices are integrated into the system using the \cleaninline{withDevice} function (see \cref{sec:withdevice}).
  29 Using \cleaninline{liftmTask}, \gls{MTASK} tasks are lifted to a device (see \cref{sec:liftmtask}).
  30 \Gls{ITASK} \glspl{SDS} are lifted to the \gls{MTASK} device using \cleaninline{liftsds} (see \cref{sec:liftmtask}).
  31
  32 \begin{figure}[ht]
  33         \centering
  34         \includestandalone{mtask_integration}
  35         \caption{\Gls{MTASK}'s integration with \gls{ITASK}.}%
  36         \label{fig:mtask_integration}
  37 \end{figure}
  38
  39 \section{Connecting edge devices}\label{sec:withdevice}
  40 When interpreted by the byte code compiler view, an \gls{MTASK} task produces a compiler.
  41 This compiler is exceuted at run time so that the resulting byte code can be sent to an edge device.
  42 All communication with this device happens through a so-called \emph{channels} \gls{SDS}.
  43 The channels contain three fields, a queue of messages that are received, a queue of messages to send and a stop flag.
  44 Every communication method that implements the \cleaninline{channelSync} class can provide the communication with an \gls{MTASK} device.
  45 As of now, serial port communication, direct \gls{TCP} communication and \gls{MQTT} over \gls{TCP} are supported as communication providers (see \cref{lst:connection_types}).
  46 The \cleaninline{withDevice} function transforms such a communication provider and a task that does something with this device to an \gls{ITASK} task.
  47 Internally, the task sets up the communication, exchanges specifications with the device, executes the inner task while handling errors, and finally cleans up after closing.
  48 \Cref{lst:mtask_device} shows the types and interface to connecting devices.
  49
  50 \begin{lstClean}[label={lst:mtask_device},caption={Device communication interface in \gls{MTASK}.}]
  51 :: MTDevice //abstract
  52 :: Channels :== ([MTMessageFro], [MTMessageTo], Bool)
  53
  54 class channelSync a :: a (Shared sds Channels) -> Task () | RWShared sds
  55
  56 withDevice :: a (MTDevice -> Task b)
  57         -> Task b | iTask b & channelSync, iTask a
  58 \end{lstClean}
  59
  60 \subsection{Implementation}
  61 \Cref{lst:pseudo_withdevice} shows a pseudocode implementation of the \cleaninline{withDevice} function.
  62 The \cleaninline{MTDevice} abstract type is internally represented as three \gls{ITASK} \gls{SDS} that contain all the current information about the tasks.
  63 The first \gls{SDS} is the information about the \gls{RTS} of the device, i.e.\ metadata on the tasks that are executing, the hardware specification and capabilities, and a list of fresh task identifiers.
  64 The second \gls{SDS} is a map storing downstream \gls{SDS} updates.
  65 When a lifted \gls{SDS} is updated on the device, a message is sent to the server.
  66 This message is initially queued in the map to allow for asynchronous handling of multiple updates.
  67 Finally, the \cleaninline{MTDevices} type contains the communication channels.
  68
  69 The \cleaninline{withDevice} task itself first constructs the \glspl{SDS} using the \gls{ITASK} function \cleaninline{withShared} to create anonymous local \glspl{SDS}.
  70 Then, it performs the following four tasks in parallel to monitor the edge device.
  71 \begin{enumerate}
  72         \item It synchronises the channels using the \cleaninline{channelSync} overloaded function.
  73                 Errors that occur here are converted to the proper \gls{MTASK} exception.
  74         \item Watches the channels for the shutdown flag.
  75                 If the connection is lost with the device unexpectedly, an \gls{MTASK} exception is thrown.
  76         \item Watches the channels for messages and processes them accordingly by changing the device information \gls{SDS} or adding the lifted \gls{SDS} updates to the corresponding \gls{SDS} update queue.
  77         \item Sends a request for a specification. Once the specification is received, the device task is run.
  78                 The task value of this device task is then used as the task value of the \cleaninline{withDevice} task.
  79 \end{enumerate}
  80
  81 \begin{lstClean}[caption={Pseudocode for the \texttt{widthDevice} function},label={lst:pseudo_withdevice}]
  82 withDevice spec deviceTask =
  83         withShared newMap \sdsupdates->
  84         withShared ([], [MTTSpecRequest], False) \channels->
  85         withShared default \dev->parallel
  86                 [ channelSync spec
  87                 , watchForShutdown
  88                 , watchChannels
  89                 , waitForSpecification
  90                         >>| deviceTask
  91                         >>* [ifStable: issueShutdown]
  92                 ]
  93 \end{lstClean}
  94
  95 If at any stage an unrecoverable device error occurs, an \gls{ITASK} exception is thrown on the \cleaninline{withDevice} task.
  96 This exception can be caught in order to device some kind of fail-safe mechanism.
  97 For example, when a device fails, the tasks can be sent to another device as can be seen in \cref{lst:failover}.
  98 This function executes an \gls{MTASK} task on a pool of devices.
  99 If an error occurs during execution, the next device in the pool is tried until the pool is exhausted
 100
 101 \begin{lstClean}[caption={An \gls{MTASK} failover combinator.},label={lst:failover}]
 102 failover :: [TCPSettings] (Main (MTask BCInterpret a)) -> Task a
 103 failover []     _     = throw "Exhausted device pool"
 104 failover [d:ds] mtask = try (withDevice d (liftmTask mtask)) except
 105 where except MTEUnexpectedDisconnect = failover ds mtask
 106           except _                       = throw e
 107 \end{lstClean}
 108
 109 \section{Lifting \texorpdfstring{\gls{MTASK}}{mTask} tasks}\label{sec:liftmtask}
 110 Once the connection with the device is established, \gls{MTASK} tasks can be lifted to \gls{MTASK} tasks using the \cleaninline{liftmTask} family of functions (see \cref{lst:liftmtask}).
 111 Given an \gls{MTASK} task in the \cleaninline{BCInterpret} view and a device obtained from \cleaninline{withDevice}, an \gls{ITASK} task is returned.
 112 This \gls{ITASK} task tethers the \gls{MTASK} task that is executed on the microcontroller.
 113 Hence, when for example observing the task value, the actual task value from the microcontroller is observed.
 114
 115 \begin{lstClean}[label={lst:liftmtask},caption={The interface for lifting \gls{MTASK} tasks to \gls{ITASK} tasks.}]
 116 liftmTask :: (Main (MTask BCInterpret a)) MTDevice -> Task a | iTask a
 117 \end{lstClean}
 118
 119 \subsection{Implementation}
 120 Under the hood, \cleaninline{liftmTask}:
 121 \begin{itemize}
 122         \item Generates a fresh task identifier for the device.
 123         \item Compiles the task and fetches the values for the tethered \glspl{SDS}.
 124         \item Sends the task to the device
 125         \item Watches, in parallel: the tethered \glspl{SDS} in \gls{ITASK}, if they are updated, a message is sent to the device; the \gls{SDS} update queue, if there is a downstream update, the \gls{ITASK} \gls{SDS} it references is updated as well; and the task value.
 126 \end{itemize}
 127
 128 The task value of the \cleaninline{liftmTask} task is the task value of the task on the edge device.
 129
 130 \todo{v.b.\ voor liftmtask}
 131
 132 \section{Lifting \texorpdfstring{\gls{ITASK}}{iTask} \texorpdfstring{\glsxtrlongpl{SDS}}{shared data sources}}\label{sec:liftsds}
 133 Lifting \gls{ITASK} \glspl{SDS} to \gls{MTASK} \glspl{SDS} is something that mostly happens at the compiler level using the \cleaninline{liftsds} function (see \cref{lst:mtask_itasksds}).
 134 \Glspl{SDS} in \gls{MTASK} must always have an initial value.
 135 For regular \gls{SDS} this value is given in the source code, for lifted \gls{ITASK} \glspl{SDS} this value is obtained by reading the values once just before sending the task to the edge device.
 136 On the device itself, there is just one difference between lifted \glspl{SDS} and regular \glspl{SDS}: after changing \pgls{SDS}, a message is sent to the server containing this new value.
 137 The \cleaninline{withDevice} task (see \cref{sec:withdevice}) receives and processes this message by writing to the \gls{ITASK} \gls{SDS}.
 138 Tasks watching this \gls{SDS} get notified then through the normal notification mechanism of \gls{ITASK}.
 139
 140 \begin{lstClean}[label={lst:mtask_itasksds},caption={Lifted \gls{ITASK} \glspl{SDS} in \gls{MTASK}.}]
 141 class liftsds v where
 142         liftsds :: ((v (Sds t)) -> In (Shared sds t) (Main (MTask v u)))
 143                 -> Main (MTask v u) | RWShared sds
 144 \end{lstClean}
 145
 146 \subsection{Implementation}
 147 The compilation of the code and the serialisation of the data throws away all typing information.
 148 \Glspl{SDS} are stored in the compiler state as a map from identifiers to either an initial value or an \cleaninline{MTLens}.
 149 The \cleaninline{MTLens} is a type synonym for a \gls{SDS} that represents the typeless serialised value of the underlying \gls{SDS}.
 150 This is done so that the \cleaninline{withDevice} task can write the received \gls{SDS} updates to the according \gls{SDS} independently.
 151 \Gls{ITASK}'s notification mechanism then takes care of the rest.
 152 Such a \gls{SDS} is created by using the \cleaninline{mapReadWriteError} which, given a pair of read and write functions with error handling, produces a \gls{SDS} with the lens embedded.
 153 The read function transforms, the function that converts a typed value to a typeless serialised value, just applies the serialisation.
 154 The write function, the function that, given the new serialised value and the old typed value, produces a new typed value.
 155 It tries to decode the serialised value, if that succeeds, it is written to the underlying \gls{SDS}, an error is thrown otherwise.
 156 \Cref{lst:mtask_itasksds_lens} provides the implementation for this:
 157
 158 % VimTeX: SynIgnore on
 159 \begin{lstClean}[label={lst:mtask_itasksds_lens},caption={Lens applied to lifted \gls{ITASK} \glspl{SDS} in \gls{MTASK}.}]
 160 lens :: (Shared sds a) -> MTLens | type a & RWShared sds
 161 lens sds = mapReadWriteError
 162         ( \r->   Ok (fromString (toByteCode{|*|} r)
 163         , \w r-> ?Just <$> iTasksDecode (toString w)
 164         ) ?None sds
 165 \end{lstClean}
 166 % VimTeX: SynIgnore off
 167
 168 \Cref{lst:mtask_itasksds_lift} shows the code for the implementation of \cleaninline{liftsds} that uses the \cleaninline{lens} function shown earlier.
 169 First, the \gls{SDS} to be lifted is extracted from the expression by bootstrapping the fixed point with a dummy value.
 170 This is safe because the expression on the right-hand side of the \cleaninline{In} is never evaluated.
 171 Then, using \cleaninline{addSdsIfNotExist}, the identifier for this particular \gls{SDS} is either retrieved from the compiler state or generated freshly.
 172 This identifier is then used to provide a reference to the \cleaninline{def} definition to evaluate the main expression.
 173
 174 % VimTeX: SynIgnore on
 175 \begin{lstClean}[label={lst:mtask_itasksds_lift},caption={Lens applied to lifted \gls{ITASK} \glspl{SDS} in \gls{MTASK}.}]
 176         liftsds def = {main =
 177                         let (t In _) = def (abort "liftsds: expression too strict")
 178                         in addSdsIfNotExist (Right $ lens t)
 179                                 >>= \sdsi->let (_ In e) = def (pure (Sds sdsi)) in e.main
 180                 }\end{lstClean}
 181 % VimTeX: SynIgnore off
 182
 183 \todo{v.b.\ voor lifted sdss}
 184
 185 \section{Home automation}
 186 This section presents a interactive home automation program (\Cref{lst:example_home_automation}) to illustrate \gls{MTASK}'s integration with \gls{ITASK}.
 187 It consists of a web interface for the user to control which tasks may be executed on either of two connected devices: an \gls{ARDUINO} UNO, connected via a serial port; and an ESP8266 based prototyping board called NodeMCU, connected via \gls{TCP} over WiFi.
 188
 189 \Crefrange{lst:example:spec1}{lst:example:spec2} show the specification for the devices.
 190 The UNO is connected via serial using the unix filepath \path{/dev/ttyACM0} and the default serial port settings.
 191 The NodeMCU is connected via WiFi and hence the \cleaninline{TCPSettings} record is used.
 192 Both types have \cleaninline{channelSync} instances.
 193
 194 The code consists of an \gls{ITASK} part and several \gls{MTASK} parts.
 195 \Crefrange{lst:example:task1}{lst:example:task2} containing the \gls{ITASK} task that coordinates the \gls{IOT} application.
 196 It first connects the devices (\crefrange{lst:example:conn1}{lst:example:conn2}) followed by launching a \cleaninline{parallel} task, visualized as a tabbed window, and a shutdown button to terminate the program (\crefrange{lst:example:par1}{lst:example:par2}).
 197 This parallel task is the controller of the tasks that run on the edge devices.
 198 It contains one task that allows adding new tasks (using \cleaninline{appendTask}) and all other tasks in the process list will be \gls{MTASK} tasks once they are added by the user.
 199 The controller task, \cleaninline{chooseTask} as shown in \crefrange{lst:example:ct1}{lst:example:ct2}, allows the user to pick a task, sending it to the specified device.
 200 Tasks are picked by index from the \cleaninline{tasks} list (\crefrange{lst:example:tasks1}{lst:example:tasks2}) using \cleaninline{enterChoice}.
 201 The interface that is generated for this can be seen in \cref{fig:example_screenshots1}.
 202 After selecting the task, a device is selected (see \cref{fig:example_screenshots2,lst:example:selectdev}).
 203 When both a task and a device is selected, an \gls{ITASK} task is added to the process list using \cleaninline{appendTask}.
 204 Using the helper function \cleaninline{mkTask}, the actual task is selected from the \cleaninline{tasks} list and executed by providing the device argument.
 205 For example, when selecting the \cleaninline{temperature} task, the current temperature is shown to the user (\cref{fig:example_screenshots3}).
 206 This task just sends a simple temperature monitoring task to the device using \cleaninline{liftmTask} and provides a view on its task value using the \cleaninline{>\&>}\footnotemark{} \gls{ITASK} combinator.
 207 \footnotetext{\cleaninline{(>\&>) infixl 1 :: (Task a) ((SDSLens () (? a) ()) -> Task b) -> Task b \| iTask a \& iTask b}}
 208 The light switch task at \crefrange{lst:example:ls1}{lst:example:ls2} is a task that has bidirectional interaction.
 209 Using \cleaninline{liftsds}, the status of the light switch is synchronised with the user.
 210 The task on the edge device continuously monitors the value of the lifted \gls{SDS}.
 211 If it is different from the current state, the new value is written to the digital \gls{GPIO} pin 13 and the monitoring function is recursively called.
 212
 213 \begin{figure}[ht]
 214         \centering
 215         \begin{subfigure}[b]{.3\linewidth}
 216                 \includegraphics[width=\linewidth]{home_auto1}
 217                 \caption{Select task.}%
 218                 \label{fig:example_screenshots1}
 219         \end{subfigure}
 220         \begin{subfigure}[b]{.3\linewidth}
 221                 \includegraphics[width=\linewidth]{home_auto2}
 222                 \caption{Select device.}%
 223                 \label{fig:example_screenshots2}
 224         \end{subfigure}
 225         \begin{subfigure}[b]{.3\linewidth}
 226                 \includegraphics[width=\linewidth]{home_auto3}
 227                 \caption{View result.}%
 228                 \label{fig:example_screenshots3}
 229         \end{subfigure}
 230         \caption{Screenshots of the home automation example program in action.}%
 231         \label{fig:example_screenshots}
 232 \end{figure}
 233
 234 \begin{figure}
 235         \cleaninputlisting[firstline=12,lastline=60,numbers=left,belowskip=0pt,escapeinside={/*}{*/}]{lst/example.icl}
 236         \begin{lstClean}[numbers=left,firstnumber=50,aboveskip=0pt,caption={An example of a home automation program.},label={lst:example_home_automation}]
 237         , ...][+\label{lst:example:tasks2}+]\end{lstClean}
 238 \end{figure}
 239
 240 \section{Conclusion}
 241 \Gls{MTASK} edge devices run little \gls{TOP} engines of their own.
 242 Using only a couple of \gls{ITASK} functions, \gls{MTASK} tasks can be integrated in \gls{ITASK} seamlessly.
 243 Devices, using any supported type of connection, are integrated in \gls{ITASK} using the \cleaninline{withDevice} function.
 244 Once connected, \gls{MTASK} tasks can be sent to the device for execution using \cleaninline{liftmTask}, lifting them to full-fledged \gls{ITASK} tasks.
 245 Furthermore, the \gls{MTASK} tasks can interact with \gls{ITASK} \glspl{SDS} using the \cleaninline{liftsds} construct.
 246 This together allows entire \gls{IOT} systems to be programmed from a single source.
 247
 248 \input{subfilepostamble}
 249 \end{document}