top/int.tex

   1 \documentclass[../thesis.tex]{subfiles}
   2
   3 \input{subfilepreamble}
   4
   5 \begin{document}
   6 \input{subfileprefix}
   7 \chapter{Integration with \texorpdfstring{\gls{ITASK}}{iTask}}%
   8 \label{chp:integration_with_itask}
   9 \begin{chapterabstract}
  10         \noindent This chapter shows the integration of \gls{MTASK} with \gls{ITASK} by showing:
  11         \begin{itemize}
  12                 \item an architectural overview \gls{MTASK} applications;
  13                 \item on the interface for connecting devices;
  14                 \item the interface for lifting \gls{MTASK} tasks to \gls{ITASK} tasks;
  15                 \item a interface for lifting \gls{ITASK} \glspl{SDS} to \gls{MTASK} \glspl{SDS};
  16                 \item and finishes with non-trivial home automation example application using all integration mechanisms;
  17         \end{itemize}
  18 \end{chapterabstract}
  19
  20 The \gls{MTASK} language is a multi-view \gls{DSL}, i.e.\ there are multiple interpretations possible for a single \gls{MTASK} term.
  21 Using the byte code compiler (\cleaninline{BCInterpret}) \gls{DSL} interpretation, \gls{MTASK} tasks can be fully integrated in \gls{ITASK}.
  22 They are executed as if they are regular \gls{ITASK} tasks and they communicate may access \glspl{SDS} from \gls{ITASK} as well.
  23 \Gls{MTASK} devices contain a domain-specific \gls{OS} and are little \gls{TOP} engines in their own respect, being able to execute tasks.
  24 \Cref{fig:mtask_integration} shows the architectural layout of a typical \gls{IOT} system created with \gls{ITASK} and \gls{MTASK}.
  25 The entire system is written as a single \gls{CLEAN} specification where multiple tasks are executed at the same time.
  26 Tasks can access \glspl{SDS} according to many-to-many communication and multiple clients can work on the same task.
  27 Devices are integrated into the system using the \cleaninline{withDevice} function (see \cref{sec:withdevice}).
  28 Using \cleaninline{liftmTask}, \gls{MTASK} tasks are lifted to a device (see \cref{sec:liftmtask}).
  29 \Gls{ITASK} \glspl{SDS} are lifted to the \gls{MTASK} device using \cleaninline{liftsds} (see \cref{sec:liftsds}).
  30
  31 \begin{figure}[ht]
  32         \centering
  33         \includestandalone{mtask_integration}
  34         \caption{\Gls{MTASK}'s integration with \gls{ITASK}.}%
  35         \label{fig:mtask_integration}
  36 \end{figure}
  37
  38 \section{Connecting edge devices}\label{sec:withdevice}
  39 When interpreted by the byte code compiler view, an \gls{MTASK} task produces a compiler.
  40 This compiler is exceuted at run time so that the resulting byte code can be sent to an edge device.
  41 All communication with this device happens through a so-called \emph{channels} \gls{SDS}.
  42 The channels contain three fields, a queue of messages that are received, a queue of messages to send and a stop flag.
  43 Every communication method that implements the \cleaninline{channelSync} class can provide the communication with an \gls{MTASK} device.
  44 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}).
  45 The \cleaninline{withDevice} function transforms such a communication provider and a task that does something with this device to an \gls{ITASK} task.
  46 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.
  47 \Cref{lst:mtask_device} shows the types and interface to connecting devices.
  48
  49 \begin{lstClean}[label={lst:mtask_device},caption={Device communication interface in \gls{MTASK}.}]
  50 :: MTDevice //abstract
  51 :: Channels :== ([MTMessageFro], [MTMessageTo], Bool)
  52
  53 class channelSync a :: a (Shared sds Channels) -> Task () | RWShared sds
  54
  55 withDevice :: a (MTDevice -> Task b)
  56         -> Task b | iTask b & channelSync, iTask a
  57 \end{lstClean}
  58
  59 \subsection{Implementation}
  60 \Cref{lst:pseudo_withdevice} shows a pseudocode implementation of the \cleaninline{withDevice} function.
  61 The \cleaninline{MTDevice} abstract type is internally represented as three \gls{ITASK} \gls{SDS} that contain all the current information about the tasks.
  62 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.
  63 The second \gls{SDS} is a map storing downstream \gls{SDS} updates.
  64 When a lifted \gls{SDS} is updated on the device, a message is sent to the server.
  65 This message is initially queued in the map to allow for asynchronous handling of multiple updates.
  66 Finally, the \cleaninline{MTDevices} type contains the communication channels.
  67
  68 The \cleaninline{withDevice} task itself first constructs the \glspl{SDS} using the \gls{ITASK} function \cleaninline{withShared} to create anonymous local \glspl{SDS}.
  69 Then, it performs the following four tasks in parallel to monitor the edge device.
  70 \begin{enumerate}
  71         \item It synchronises the channels using the \cleaninline{channelSync} overloaded function.
  72                 Errors that occur here are converted to the proper \gls{MTASK} exception.
  73         \item Watches the channels for the shutdown flag.
  74                 If the connection is lost with the device unexpectedly, an \gls{MTASK} exception is thrown.
  75         \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.
  76         \item Sends a request for a specification. Once the specification is received, the device task is run.
  77                 The task value of this device task is then used as the task value of the \cleaninline{withDevice} task.
  78 \end{enumerate}
  79
  80 \begin{lstClean}[caption={Pseudocode for the \texttt{widthDevice} function},label={lst:pseudo_withdevice}]
  81 withDevice spec deviceTask =
  82         withShared newMap \sdsupdates->
  83         withShared ([], [MTTSpecRequest], False) \channels->
  84         withShared default \dev->parallel
  85                 [ channelSync spec channels
  86                 , watchForShutdown channels
  87                 , watchChannelMessages dev channels
  88                 , waitForSpecification
  89                         >>| deviceTask
  90                         >>* [ifStable: issueShutdown]
  91                 ]
  92 \end{lstClean}
  93
  94 If at any stage an unrecoverable device error occurs, an \gls{ITASK} exception is thrown on the \cleaninline{withDevice} task.
  95 This exception can be caught in order to device some kind of fail-safe mechanism.
  96 For example, when a device fails, the tasks can be sent to another device as can be seen in \cref{lst:failover}.
  97 This function executes an \gls{MTASK} task on a pool of devices.
  98 If an error occurs during execution, the next device in the pool is tried until the pool is exhausted
  99
 100 \begin{lstClean}[caption={An \gls{MTASK} failover combinator.},label={lst:failover}]
 101 failover :: [TCPSettings] (Main (MTask BCInterpret a)) -> Task a
 102 failover []     _     = throw "Exhausted device pool"
 103 failover [d:ds] mtask = try (withDevice d (liftmTask mtask)) except
 104 where except MTEUnexpectedDisconnect = failover ds mtask
 105           except _                       = throw e
 106 \end{lstClean}
 107
 108 \section{Lifting \texorpdfstring{\gls{MTASK}}{mTask} tasks}\label{sec:liftmtask}
 109 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}).
 110 Given an \gls{MTASK} task in the \cleaninline{BCInterpret} view and a device obtained from \cleaninline{withDevice}, an \gls{ITASK} task is returned.
 111 This \gls{ITASK} task tethers the \gls{MTASK} task that is executed on the microcontroller.
 112 Hence, when for example observing the task value, the actual task value from the microcontroller is observed.
 113
 114 \begin{lstClean}[label={lst:liftmtask},caption={The interface for lifting \gls{MTASK} tasks to \gls{ITASK} tasks.}]
 115 liftmTask :: (Main (MTask BCInterpret a)) MTDevice -> Task a | iTask a
 116 \end{lstClean}
 117
 118 \subsection{Implementation}
 119 \Cref{lst:liftmTask_pseudo} shows the pseudocode for the \cleaninline{liftmTask} implementation
 120 The first argument is the task and the second argument is the device which is just an \gls{ADT} containing the \glspl{SDS} referring to the device information, the \gls{SDS} update queue, and the channels.
 121 First a fresh identifier for the task is generated using the device state.
 122 With this identifier, the cleanup hook can be installed.
 123 This is done to assure the task is removed from the edge device if the \gls{ITASK} task coordinating it is destroyed.
 124 Tasks can be destroyed when for example a task executed in parallel and the parallel combinator terminates or when the condition to step holds in a sequential task combination.
 125 Then the \gls{MTASK} compiler is invoked, its only argument besides the task is a function doing something with the results of the compilation, i.e.\ the lifted \glspl{SDS} and the messages containing the compiled and serialised task.
 126 With the result of the compilation, the task can be executed.
 127 First the messages are put in the channels, sending them to the device.
 128 Then, in parallel:
 129 \begin{enumerate*}
 130         \item the value is watched by looking in the device state \gls{SDS}, this task also determines the task value of the whole task
 131         \item the downstream \glspl{SDS} are monitored, i.e.\ the \cleaninline{sdsupdates} \gls{SDS} is monitored and updates from the device are applied to the associated \gls{ITASK} \gls{SDS}
 132         \item the upstroam \glspl{SDS} are monitored by spawning tasks that watch these \glspl{SDS}, if one is updated, the novel value is sent to the edge device.
 133 \end{enumerate*}
 134
 135 \begin{lstClean}[label={lst:liftmTask_pseudo},caption={Pseudocode implementation for \texttt{liftmTask}.}]
 136 liftmTask task (MTDevice dev sdsupdates channels)
 137         = freshTaskId dev
 138         >>= \tid->withCleanupHook (sendmessage [MTTTaskDel tid] channels) (
 139                 compile task \mrefs msgs->
 140                         sendMessage msgs channels
 141                         >>| waitForReturnAndValue tid dev
 142                         -|| watchSharesDownstream mrefs tid sdsupdates
 143                         -|| watchSharesUpstream mrefs channels tid)
 144 \end{lstClean}
 145
 146 \section{Lifting \texorpdfstring{\gls{ITASK}}{iTask} \texorpdfstring{\glsxtrlongpl{SDS}}{shared data sources}}\label{sec:liftsds}
 147 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}).
 148 \Glspl{SDS} in \gls{MTASK} must always have an initial value.
 149 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.
 150 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.
 151 The \cleaninline{withDevice} task (see \cref{sec:withdevice}) receives and processes this message by writing to the \gls{ITASK} \gls{SDS}.
 152 Tasks watching this \gls{SDS} get notified then through the normal notification mechanism of \gls{ITASK}.
 153
 154 \begin{lstClean}[label={lst:mtask_itasksds},caption={Lifted \gls{ITASK} \glspl{SDS} in \gls{MTASK}.}]
 155 class liftsds v where
 156         liftsds :: ((v (Sds t)) -> In (Shared sds t) (Main (MTask v u)))
 157                 -> Main (MTask v u) | RWShared sds
 158 \end{lstClean}
 159
 160 As an example, \cref{lst:mtask_liftsds_ex} shows a lightswitch function producing an \imtask{} task.
 161 Given an \cleaninline{MTDevice} type, a device handle, an \gls{ITASK} \gls{SDS} of the type boolean is created.
 162 This boolean represents the state of the light.
 163 The \gls{MTASK} task uses this \gls{SDS} to turn on or off the light.
 164 An \gls{ITASK} task that runs in parallel allows interactive updating of this state.
 165
 166 \todo{dit voor\-beeld aan\-hou\-den of al\-leen die gro\-te ge\-brui\-ken}
 167 \begin{lstClean}[label={lst:mtask_liftsds_ex},caption={Interactive light switch program.}]
 168 lightswitch dev  =
 169         withShared False \sh->
 170                     liftmTask (mtask sh) dev
 171                 -|| updateSharedInformation [] sh
 172                 <<@ Hint "Light switch"
 173 where
 174         mtask sh =
 175                 declarePin D13 PMOutput \d13->
 176                 liftsds \ls=sh
 177                 In fun \f=(\st->
 178                              getSds ls
 179                         >>*. [IfValue ((!=.)st) (\v->writeD d13 v)]
 180                         >>|. f (Not st))
 181                 In {main=f true}
 182 \end{lstClean}
 183
 184 \subsection{Implementation}
 185 The compilation of the code and the serialisation of the data throws away all typing information.
 186 \Glspl{SDS} are stored in the compiler state as a map from identifiers to either an initial value or an \cleaninline{MTLens}.
 187 The \cleaninline{MTLens} is a type synonym for a \gls{SDS} that represents the typeless serialised value of the underlying \gls{SDS}.
 188 This is done so that the \cleaninline{withDevice} task can write the received \gls{SDS} updates to the according \gls{SDS} independently.
 189 \Gls{ITASK}'s notification mechanism then takes care of the rest.
 190 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.
 191 The read function transforms, the function that converts a typed value to a typeless serialised value, just applies the serialisation.
 192 The write function, the function that, given the new serialised value and the old typed value, produces a new typed value.
 193 It tries to decode the serialised value, if that succeeds, it is written to the underlying \gls{SDS}, an error is thrown otherwise.
 194 \Cref{lst:mtask_itasksds_lens} provides the implementation for this:
 195
 196 % VimTeX: SynIgnore on
 197 \begin{lstClean}[label={lst:mtask_itasksds_lens},caption={Lens applied to lifted \gls{ITASK} \glspl{SDS} in \gls{MTASK}.}]
 198 lens :: (Shared sds a) -> MTLens | type a & RWShared sds
 199 lens sds = mapReadWriteError
 200         ( \r->   Ok (fromString (toByteCode{|*|} r)
 201         , \w r-> ?Just <$> iTasksDecode (toString w)
 202         ) ?None sds
 203 \end{lstClean}
 204 % VimTeX: SynIgnore off
 205
 206 \Cref{lst:mtask_itasksds_lift} shows the code for the implementation of \cleaninline{liftsds} that uses the \cleaninline{lens} function shown earlier.
 207 First, the \gls{SDS} to be lifted is extracted from the expression by bootstrapping the fixed point with a dummy value.
 208 This is safe because the expression on the right-hand side of the \cleaninline{In} is never evaluated.
 209 Then, using \cleaninline{addSdsIfNotExist}, the identifier for this particular \gls{SDS} is either retrieved from the compiler state or generated freshly.
 210 This identifier is then used to provide a reference to the \cleaninline{def} definition to evaluate the main expression.
 211
 212 % VimTeX: SynIgnore on
 213 \begin{lstClean}[label={lst:mtask_itasksds_lift},caption={Lens applied to lifted \gls{ITASK} \glspl{SDS} in \gls{MTASK}.}]
 214         liftsds def = {main =
 215                         let (t In _) = def (abort "liftsds: expression too strict")
 216                         in addSdsIfNotExist (Right $ lens t)
 217                                 >>= \sdsi->let (_ In e) = def (pure (Sds sdsi)) in e.main
 218                 }\end{lstClean}
 219 % VimTeX: SynIgnore off
 220
 221 \section{Home automation}
 222 This section presents a interactive home automation program (\Cref{lst:example_home_automation}) to illustrate \gls{MTASK}'s integration with \gls{ITASK}.
 223 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.
 224
 225 \Crefrange{lst:example:spec1}{lst:example:spec2} show the specification for the devices.
 226 The UNO is connected via serial using the unix filepath \path{/dev/ttyACM0} and the default serial port settings.
 227 The NodeMCU is connected via WiFi and hence the \cleaninline{TCPSettings} record is used.
 228 Both types have \cleaninline{channelSync} instances.
 229
 230 The code consists of an \gls{ITASK} part and several \gls{MTASK} parts.
 231 \Crefrange{lst:example:task1}{lst:example:task2} containing the \gls{ITASK} task that coordinates the \gls{IOT} application.
 232 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}).
 233 This parallel task is the controller of the tasks that run on the edge devices.
 234 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.
 235 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.
 236 Tasks are picked by index from the \cleaninline{tasks} list (\crefrange{lst:example:tasks1}{lst:example:tasks2}) using \cleaninline{enterChoice}.
 237 The interface that is generated for this can be seen in \cref{fig:example_screenshots1}.
 238 After selecting the task, a device is selected (see \cref{fig:example_screenshots2,lst:example:selectdev}).
 239 When both a task and a device is selected, an \gls{ITASK} task is added to the process list using \cleaninline{appendTask}.
 240 Using the helper function \cleaninline{mkTask}, the actual task is selected from the \cleaninline{tasks} list and executed by providing the device argument.
 241 For example, when selecting the \cleaninline{temperature} task, the current temperature is shown to the user (\cref{fig:example_screenshots3}).
 242 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.
 243 \footnotetext{\cleaninline{(>\&>) infixl 1 :: (Task a) ((SDSLens () (? a) ()) -> Task b) -> Task b \| iTask a \& iTask b}}
 244 The light switch task at \crefrange{lst:example:ls1}{lst:example:ls2} is a task that has bidirectional interaction using the definition of \cleaninline{lightswitch} shown in \cref{lst:mtask_liftsds_ex}.
 245 Using \cleaninline{liftsds}, the status of the light switch is synchronised with the user.
 246 The task on the edge device continuously monitors the value of the lifted \gls{SDS}.
 247 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.
 248
 249 \begin{figure}[ht]
 250         \centering
 251         \begin{subfigure}[b]{.3\linewidth}
 252                 \includegraphics[width=\linewidth]{home_auto1}
 253                 \caption{Select task.}%
 254                 \label{fig:example_screenshots1}
 255         \end{subfigure}
 256         \begin{subfigure}[b]{.3\linewidth}
 257                 \includegraphics[width=\linewidth]{home_auto2}
 258                 \caption{Select device.}%
 259                 \label{fig:example_screenshots2}
 260         \end{subfigure}
 261         \begin{subfigure}[b]{.3\linewidth}
 262                 \includegraphics[width=\linewidth]{home_auto3}
 263                 \caption{View result.}%
 264                 \label{fig:example_screenshots3}
 265         \end{subfigure}
 266         \caption{Screenshots of the home automation example program in action.}%
 267         \label{fig:example_screenshots}
 268 \end{figure}
 269
 270 \begin{figure}
 271         \cleaninputlisting[firstline=12,lastline=50,numbers=left,belowskip=0pt]{lst/example.icl}
 272         \begin{lstClean}[numbers=left,firstnumber=40,aboveskip=0pt,caption={An example of a home automation program.},label={lst:example_home_automation}]
 273         , ...][+\label{lst:example:tasks2}+]\end{lstClean}
 274 \end{figure}
 275
 276 \section{Conclusion}
 277 \Gls{MTASK} edge devices run little \gls{TOP} engines of their own.
 278 Using only a couple of \gls{ITASK} functions, \gls{MTASK} tasks can be integrated in \gls{ITASK} seamlessly.
 279 Devices, using any supported type of connection, are integrated in \gls{ITASK} using the \cleaninline{withDevice} function.
 280 Once connected, \gls{MTASK} tasks can be sent to the device for execution using \cleaninline{liftmTask}, lifting them to full-fledged \gls{ITASK} tasks.
 281 Furthermore, the \gls{MTASK} tasks can interact with \gls{ITASK} \glspl{SDS} using the \cleaninline{liftsds} construct.
 282 This together allows entire \gls{IOT} systems to be programmed from a single source.
 283
 284 \input{subfilepostamble}
 285 \end{document}