\begin{document}
\input{subfileprefix}
-
\chapter{Integration with \texorpdfstring{\gls{ITASK}}{iTask}}%
\label{chp:integration_with_itask}
\begin{chapterabstract}
- This chapter shows the integration of \gls{MTASK} with \gls{ITASK} by showing:
+ \noindent This chapter shows the integration of \gls{MTASK} with \gls{ITASK} by showing:
\begin{itemize}
- \item an architectural overview of \gls{MTASK};
+ \item an architectural overview \gls{MTASK} applications;
\item on the interface for connecting devices;
\item the interface for lifting \gls{MTASK} tasks to \gls{ITASK} tasks;
- \item and interface for lifting \gls{ITASK} \glspl{SDS} to \gls{MTASK} \glspl{SDS}.
+ \item a interface for lifting \gls{ITASK} \glspl{SDS} to \gls{MTASK} \glspl{SDS};
+ \item and finishes with non-trivial home automation example application using all integration mechanisms;
\end{itemize}
\end{chapterabstract}
The \gls{MTASK} language is a multi-view \gls{DSL}, i.e.\ there are multiple interpretations possible for a single \gls{MTASK} term.
Using the byte code compiler (\cleaninline{BCInterpret}) \gls{DSL} interpretation, \gls{MTASK} tasks can be fully integrated in \gls{ITASK}.
They are executed as if they are regular \gls{ITASK} tasks and they communicate may access \glspl{SDS} from \gls{ITASK} as well.
-\Gls{MTASK} devices contain a domain-specific \gls{OS} (\gls{RTS}) and are little \gls{TOP} engines in their own respect, being able to execute tasks.
+\Gls{MTASK} devices contain a domain-specific \gls{OS} and are little \gls{TOP} engines in their own respect, being able to execute tasks.
\Cref{fig:mtask_integration} shows the architectural layout of a typical \gls{IOT} system created with \gls{ITASK} and \gls{MTASK}.
The entire system is written as a single \gls{CLEAN} specification where multiple tasks are executed at the same time.
Tasks can access \glspl{SDS} according to many-to-many communication and multiple clients can work on the same task.
Devices are integrated into the system using the \cleaninline{withDevice} function (see \cref{sec:withdevice}).
Using \cleaninline{liftmTask}, \gls{MTASK} tasks are lifted to a device (see \cref{sec:liftmtask}).
-\Gls{ITASK} \glspl{SDS} are lifted to the \gls{MTASK} device using \cleaninline{liftsds} (see \cref{sec:liftmtask}).
+\Gls{ITASK} \glspl{SDS} are lifted to the \gls{MTASK} device using \cleaninline{liftsds} (see \cref{sec:liftsds}).
\begin{figure}[ht]
\centering
\label{fig:mtask_integration}
\end{figure}
-\section{Devices}\label{sec:withdevice}
+\section{Connecting edge devices}\label{sec:withdevice}
When interpreted by the byte code compiler view, an \gls{MTASK} task produces a compiler.
This compiler is exceuted at run time so that the resulting byte code can be sent to an edge device.
All communication with this device happens through a so-called \emph{channels} \gls{SDS}.
The channels contain three fields, a queue of messages that are received, a queue of messages to send and a stop flag.
Every communication method that implements the \cleaninline{channelSync} class can provide the communication with an \gls{MTASK} device.
-As of now, serial port communication, direct \gls{TCP} communication and \gls{MQTT} over \gls{TCP} are supported as communication providers.
-The \cleaninline{withDevice} function transforms a communication provider and a task that does something with this device to an \gls{ITASK} task.
-Internally, the task sets up the communication, exchanges specifications, executes the inner task while handling errors, and finally cleans up after closing.
+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}).
+The \cleaninline{withDevice} function transforms such a communication provider and a task that does something with this device to an \gls{ITASK} task.
+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.
\Cref{lst:mtask_device} shows the types and interface to connecting devices.
\begin{lstClean}[label={lst:mtask_device},caption={Device communication interface in \gls{MTASK}.}]
class channelSync a :: a (Shared sds Channels) -> Task () | RWShared sds
-withDevice :: a (MTDevice -> Task b) -> Task b | iTask b & channelSync, iTask a
+withDevice :: a (MTDevice -> Task b)
+ -> Task b | iTask b & channelSync, iTask a
+\end{lstClean}
+
+\subsection{Implementation}
+\Cref{lst:pseudo_withdevice} shows a pseudocode implementation of the \cleaninline{withDevice} function.
+The \cleaninline{MTDevice} abstract type is internally represented as three \gls{ITASK} \gls{SDS} that contain all the current information about the tasks.
+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.
+The second \gls{SDS} is a map storing downstream \gls{SDS} updates.
+When a lifted \gls{SDS} is updated on the device, a message is sent to the server.
+This message is initially queued in the map to allow for asynchronous handling of multiple updates.
+Finally, the \cleaninline{MTDevices} type contains the communication channels.
+
+The \cleaninline{withDevice} task itself first constructs the \glspl{SDS} using the \gls{ITASK} function \cleaninline{withShared} to create anonymous local \glspl{SDS}.
+Then, it performs the following four tasks in parallel to monitor the edge device.
+\begin{enumerate}
+ \item It synchronises the channels using the \cleaninline{channelSync} overloaded function.
+ Errors that occur here are converted to the proper \gls{MTASK} exception.
+ \item Watches the channels for the shutdown flag.
+ If the connection is lost with the device unexpectedly, an \gls{MTASK} exception is thrown.
+ \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.
+ \item Sends a request for a specification. Once the specification is received, the device task is run.
+ The task value of this device task is then used as the task value of the \cleaninline{withDevice} task.
+\end{enumerate}
+
+\begin{lstClean}[caption={Pseudocode for the \texttt{widthDevice} function},label={lst:pseudo_withdevice}]
+withDevice spec deviceTask =
+ withShared newMap \sdsupdates->
+ withShared ([], [MTTSpecRequest], False) \channels->
+ withShared default \dev->parallel
+ [ channelSync spec channels
+ , watchForShutdown channels
+ , watchChannelMessages dev channels
+ , waitForSpecification
+ >>| deviceTask
+ >>* [ifStable: issueShutdown]
+ ]
+\end{lstClean}
+
+If at any stage an unrecoverable device error occurs, an \gls{ITASK} exception is thrown on the \cleaninline{withDevice} task.
+This exception can be caught in order to device some kind of fail-safe mechanism.
+For example, when a device fails, the tasks can be sent to another device as can be seen in \cref{lst:failover}.
+This function executes an \gls{MTASK} task on a pool of devices.
+If an error occurs during execution, the next device in the pool is tried until the pool is exhausted
+
+\begin{lstClean}[caption={An \gls{MTASK} failover combinator.},label={lst:failover}]
+failover :: [TCPSettings] (Main (MTask BCInterpret a)) -> Task a
+failover [] _ = throw "Exhausted device pool"
+failover [d:ds] mtask = try (withDevice d (liftmTask mtask)) except
+where except MTEUnexpectedDisconnect = failover ds mtask
+ except _ = throw e
\end{lstClean}
-\section{Lifting tasks}\label{sec:liftmtask}
+\section{Lifting \texorpdfstring{\gls{MTASK}}{mTask} tasks}\label{sec:liftmtask}
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}).
Given an \gls{MTASK} task in the \cleaninline{BCInterpret} view and a device obtained from \cleaninline{withDevice}, an \gls{ITASK} task is returned.
This \gls{ITASK} task tethers the \gls{MTASK} task that is executed on the microcontroller.
Hence, when for example observing the task value, the actual task value from the microcontroller is observed.
\begin{lstClean}[label={lst:liftmtask},caption={The interface for lifting \gls{MTASK} tasks to \gls{ITASK} tasks.}]
-liftmTask :: (Main (MTask BCInterpret u)) MTDevice -> Task u | iTask u
+liftmTask :: (Main (MTask BCInterpret a)) MTDevice -> Task a | iTask a
\end{lstClean}
-Under the hood, \cleaninline{liftmTask} compiler the \gls{MTASK} task to byte code, gathers the initial values for the lifted \glspl{SDS} and sends the data to the device.
-Once acknowledged, the \gls{MTASK} task value and the \glspl{SDS} are monitored.
-If the \gls{ITASK} server updates the value of a lifted \gls{SDS}, the appropriate message is sent to the \gls{MTASK} to notify it of the change.
-Furthermore, the \gls{MTASK} device may update the \gls{SDS}, and in that case the message is picked up by the \cleaninline{liftmTask} task and the \gls{SDS} on the \gls{ITASK} server updated accordingly.
+\subsection{Implementation}
+\Cref{lst:liftmTask_pseudo} shows the pseudocode for the \cleaninline{liftmTask} implementation
+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.
+First a fresh identifier for the task is generated using the device state.
+With this identifier, the cleanup hook can be installed.
+This is done to assure the task is removed from the edge device if the \gls{ITASK} task coordinating it is destroyed.
+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.
+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.
+With the result of the compilation, the task can be executed.
+First the messages are put in the channels, sending them to the device.
+Then, in parallel:
+\begin{enumerate*}
+ \item the value is watched by looking in the device state \gls{SDS}, this task also determines the task value of the whole task
+ \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}
+ \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.
+\end{enumerate*}
+
+\begin{lstClean}[label={lst:liftmTask_pseudo},caption={Pseudocode implementation for \texttt{liftmTask}.}]
+liftmTask task (MTDevice dev sdsupdates channels)
+ = freshTaskId dev
+ >>= \tid->withCleanupHook (sendmessage [MTTTaskDel tid] channels) (
+ compile task \mrefs msgs->
+ sendMessage msgs channels
+ >>| waitForReturnAndValue tid dev
+ -|| watchSharesDownstream mrefs tid sdsupdates
+ -|| watchSharesUpstream mrefs channels tid)
+\end{lstClean}
+
+\section{Lifting \texorpdfstring{\gls{ITASK}}{iTask} \texorpdfstring{\glsxtrlongpl{SDS}}{shared data sources}}\label{sec:liftsds}
+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}).
+\Glspl{SDS} in \gls{MTASK} must always have an initial value.
+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.
+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.
+The \cleaninline{withDevice} task (see \cref{sec:withdevice}) receives and processes this message by writing to the \gls{ITASK} \gls{SDS}.
+Tasks watching this \gls{SDS} get notified then through the normal notification mechanism of \gls{ITASK}.
-\section{Lifting \texorpdfstring{\glsxtrlongpl{SDS}}{shared data sources}}\label{sec:liftsds}
\begin{lstClean}[label={lst:mtask_itasksds},caption={Lifted \gls{ITASK} \glspl{SDS} in \gls{MTASK}.}]
class liftsds v where
liftsds :: ((v (Sds t)) -> In (Shared sds t) (Main (MTask v u)))
-> Main (MTask v u) | RWShared sds
\end{lstClean}
-\section{Conclusion}
+As an example, \cref{lst:mtask_liftsds_ex} shows a lightswitch function producing an \imtask{} task.
+Given an \cleaninline{MTDevice} type, a device handle, an \gls{ITASK} \gls{SDS} of the type boolean is created.
+This boolean represents the state of the light.
+The \gls{MTASK} task uses this \gls{SDS} to turn on or off the light.
+An \gls{ITASK} task that runs in parallel allows interactive updating of this state.
+
+\todo{dit voorbeeld aanhouden of alleen die grote gebruiken}
+\begin{lstClean}[label={lst:mtask_liftsds_ex},caption={Interactive light switch program.}]
+lightswitch dev =
+ withShared False \sh->
+ liftmTask (mtask sh) dev
+ -|| updateSharedInformation [] sh
+ <<@ Hint "Light switch"
+where
+ mtask sh =
+ declarePin D13 PMOutput \d13->
+ liftsds \ls=sh
+ In fun \f=(\st->
+ getSds ls
+ >>*. [IfValue ((!=.)st) (\v->writeD d13 v)]
+ >>|. f (Not st))
+ In {main=f true}
+\end{lstClean}
+
+\subsection{Implementation}
+The compilation of the code and the serialisation of the data throws away all typing information.
+\Glspl{SDS} are stored in the compiler state as a map from identifiers to either an initial value or an \cleaninline{MTLens}.
+The \cleaninline{MTLens} is a type synonym for a \gls{SDS} that represents the typeless serialised value of the underlying \gls{SDS}.
+This is done so that the \cleaninline{withDevice} task can write the received \gls{SDS} updates to the according \gls{SDS} independently.
+\Gls{ITASK}'s notification mechanism then takes care of the rest.
+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.
+The read function transforms, the function that converts a typed value to a typeless serialised value, just applies the serialisation.
+The write function, the function that, given the new serialised value and the old typed value, produces a new typed value.
+It tries to decode the serialised value, if that succeeds, it is written to the underlying \gls{SDS}, an error is thrown otherwise.
+\Cref{lst:mtask_itasksds_lens} provides the implementation for this:
+% VimTeX: SynIgnore on
+\begin{lstClean}[label={lst:mtask_itasksds_lens},caption={Lens applied to lifted \gls{ITASK} \glspl{SDS} in \gls{MTASK}.}]
+lens :: (Shared sds a) -> MTLens | type a & RWShared sds
+lens sds = mapReadWriteError
+ ( \r-> Ok (fromString (toByteCode{|*|} r)
+ , \w r-> ?Just <$> iTasksDecode (toString w)
+ ) ?None sds
+\end{lstClean}
+% VimTeX: SynIgnore off
+
+\Cref{lst:mtask_itasksds_lift} shows the code for the implementation of \cleaninline{liftsds} that uses the \cleaninline{lens} function shown earlier.
+First, the \gls{SDS} to be lifted is extracted from the expression by bootstrapping the fixed point with a dummy value.
+This is safe because the expression on the right-hand side of the \cleaninline{In} is never evaluated.
+Then, using \cleaninline{addSdsIfNotExist}, the identifier for this particular \gls{SDS} is either retrieved from the compiler state or generated freshly.
+This identifier is then used to provide a reference to the \cleaninline{def} definition to evaluate the main expression.
+
+% VimTeX: SynIgnore on
+\begin{lstClean}[label={lst:mtask_itasksds_lift},caption={Lens applied to lifted \gls{ITASK} \glspl{SDS} in \gls{MTASK}.}]
+ liftsds def = {main =
+ let (t In _) = def (abort "liftsds: expression too strict")
+ in addSdsIfNotExist (Right $ lens t)
+ >>= \sdsi->let (_ In e) = def (pure (Sds sdsi)) in e.main
+ }\end{lstClean}
+% VimTeX: SynIgnore off
+
+\section{Home automation}
+This section presents a interactive home automation program (\Cref{lst:example_home_automation}) to illustrate \gls{MTASK}'s integration with \gls{ITASK}.
+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.
+
+\Crefrange{lst:example:spec1}{lst:example:spec2} show the specification for the devices.
+The UNO is connected via serial using the unix filepath \path{/dev/ttyACM0} and the default serial port settings.
+The NodeMCU is connected via WiFi and hence the \cleaninline{TCPSettings} record is used.
+Both types have \cleaninline{channelSync} instances.
+
+The code consists of an \gls{ITASK} part and several \gls{MTASK} parts.
+\Crefrange{lst:example:task1}{lst:example:task2} containing the \gls{ITASK} task that coordinates the \gls{IOT} application.
+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}).
+This parallel task is the controller of the tasks that run on the edge devices.
+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.
+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.
+Tasks are picked by index from the \cleaninline{tasks} list (\crefrange{lst:example:tasks1}{lst:example:tasks2}) using \cleaninline{enterChoice}.
+The interface that is generated for this can be seen in \cref{fig:example_screenshots1}.
+After selecting the task, a device is selected (see \cref{fig:example_screenshots2,lst:example:selectdev}).
+When both a task and a device is selected, an \gls{ITASK} task is added to the process list using \cleaninline{appendTask}.
+Using the helper function \cleaninline{mkTask}, the actual task is selected from the \cleaninline{tasks} list and executed by providing the device argument.
+For example, when selecting the \cleaninline{temperature} task, the current temperature is shown to the user (\cref{fig:example_screenshots3}).
+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.
+\footnotetext{\cleaninline{(>\&>) infixl 1 :: (Task a) ((SDSLens () (? a) ()) -> Task b) -> Task b \| iTask a \& iTask b}}
+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}.
+Using \cleaninline{liftsds}, the status of the light switch is synchronised with the user.
+The task on the edge device continuously monitors the value of the lifted \gls{SDS}.
+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.
+
+\begin{figure}[ht]
+ \centering
+ \begin{subfigure}[b]{.3\linewidth}
+ \includegraphics[width=\linewidth]{home_auto1}
+ \caption{Select task.}%
+ \label{fig:example_screenshots1}
+ \end{subfigure}
+ \begin{subfigure}[b]{.3\linewidth}
+ \includegraphics[width=\linewidth]{home_auto2}
+ \caption{Select device.}%
+ \label{fig:example_screenshots2}
+ \end{subfigure}
+ \begin{subfigure}[b]{.3\linewidth}
+ \includegraphics[width=\linewidth]{home_auto3}
+ \caption{View result.}%
+ \label{fig:example_screenshots3}
+ \end{subfigure}
+ \caption{Screenshots of the home automation example program in action.}%
+ \label{fig:example_screenshots}
+\end{figure}
+
+\begin{figure}
+ \cleaninputlisting[firstline=12,lastline=50,numbers=left,belowskip=0pt,escapeinside={/*}{*/}]{lst/example.icl}
+ \begin{lstClean}[numbers=left,firstnumber=40,aboveskip=0pt,caption={An example of a home automation program.},label={lst:example_home_automation}]
+ , ...][+\label{lst:example:tasks2}+]\end{lstClean}
+\end{figure}
+
+\section{Conclusion}
+\Gls{MTASK} edge devices run little \gls{TOP} engines of their own.
+Using only a couple of \gls{ITASK} functions, \gls{MTASK} tasks can be integrated in \gls{ITASK} seamlessly.
+Devices, using any supported type of connection, are integrated in \gls{ITASK} using the \cleaninline{withDevice} function.
+Once connected, \gls{MTASK} tasks can be sent to the device for execution using \cleaninline{liftmTask}, lifting them to full-fledged \gls{ITASK} tasks.
+Furthermore, the \gls{MTASK} tasks can interact with \gls{ITASK} \glspl{SDS} using the \cleaninline{liftsds} construct.
+This together allows entire \gls{IOT} systems to be programmed from a single source.
\input{subfilepostamble}
\end{document}
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