results.itasks.tex

   1 The server side of the system is written in \gls{iTasks}. Functions for managing
   2 devices, \glspl{Task} and \glspl{SDS} have been created to support the
   3 functionality. An interactive application has been created that
   4 allows an interactive management console for the \gls{mTask} system. This
   5 interface provides functionality to list \glspl{SDS}, add \glspl{Task}, remove
   6 \glspl{Task}, administrate devices and view the state of the system.
   7
   8 \section{Integration}
   9 When the system starts up the devices from the previous execution still
  10 residing in the \gls{SDS} must be cleaned up. It might be the case that they
  11 contain \glspl{Task}, \glspl{SDS} or errors that are no longer applicable in
  12 this run. A user or programmer can later choose to reconnect to some devices.
  13
  14 \begin{lstlisting}[caption={Starting up the devices},%
  15         label={lst:startupdevs}]
  16 startupDevices :: Task [MTaskDevice]
  17 startupDevices = upd (map reset) deviceStoreNP
  18         where reset d = {d & deviceTask=Nothing, deviceTasks=[], deviceError=Nothing}
  19 \end{lstlisting}
  20
  21 An image of the management interface is shown in Figure~\ref{lst:manage}.
  22 The system management is done by a single \gls{Task} called \CI{mTaskManager}.
  23 To manage the system, a couple of different functionalities are needed and
  24 are launched. The left sidebar of the interface shows the list of example
  25 \glspl{Task} that are present in the system. When clicking a \gls{Task}, a
  26 dialog opens in which you can select the device to send the \gls{Task} to. The
  27 dialog might contain user specified variables. All example \glspl{mTask} are of
  28 the type \CI{Task (Main (ByteCode () Stmt))} and can thus ask for user input
  29 first.
  30
  31 The bottom panel shows the device information. In this panel, the devices can
  32 be created and modified. Moreover, this panel allows the user to reconnect with
  33 a device after a restart of the server application.
  34
  35 \begin{figure}[H]
  36         \centering
  37         \includegraphics[width=\linewidth]{manage}
  38         \caption{The device management interface}\label{lst:manageme}
  39 \end{figure}
  40
  41 \section{Shares}
  42 The architecture of the system stores the \glspl{SDS} in the \gls{SDS} that
  43 stores the list of devices. This means that if a \gls{SDS} updates, everyone
  44 watching it will be notified. This would result in to a lot of notifications
  45 that are not ment to be for the listener. Moreover, when a client updates the
  46 \gls{SDS} this is processed by the connection handler and results in an update
  47 of the real \gls{SDS}. When an \gls{iTasks}-\gls{Task} writes to a \gls{SDS}
  48 this is not passed on to the device.
  49
  50 To solve the problem, parametric lenses are used on the device storage.
  51 Listing~\ref{lst:actualdev} shows the actual types for the device storage.
  52 Programmers wanting to access the entire \gls{SDS} use the \CI{deviceStoreNP}.
  53 Programmers wanting to access a single \gls{SDS} on a device can use the
  54 \CI{getRealShare} function which is a wrapper around the \CI{deviceStore} which
  55 applies a parametric lens to the \gls{SDS}.
  56
  57 \begin{lstlisting}[label={lst:actualdev},%
  58         caption={Real types for the device \gls{SDS}}]
  59 deviceStoreNP :: Shared [MTaskDevice]
  60 deviceStore :: RWShared (Maybe (MTaskDevice, Int)) [MTaskDevice] [MTaskDevice]
  61
  62 realDeviceStore :: Shared [MTaskDevice]
  63
  64 getRealShare :: MTaskDevice MTaskShare -> Shared BCValue
  65 \end{lstlisting}
  66
  67 \subsection{Parametric Lens}
  68 The type of the parametric lens is \CI{Maybe (MTaskDevice, Int)} where the
  69 \CI{Int} is the identifier of the \gls{SDS}. The \gls{iTasks} way of applying
  70 lenses is through the \CI{sdsFocus} function and through the \CI{sdsLens}
  71 functions. \CI{sdsFocus} allows the programmer to fix the parameter.
  72 \CI{sdsLens} is basically a \CI{mapReadWrite} that has access to the parameter.
  73 This allows the programmer to create filters and lenses. Both of the methods
  74 are not good enough for the device \gls{SDS} because they do not achieve the
  75 writing to the actual device. Writing to a device requires being able to write
  76 to \glspl{SDS}. To solve this problem, a real base \gls{SDS} is created. All
  77 the details are visible in Listing~\ref{shareimpl}.
  78 \todo{elaborate}
  79
  80 \begin{lstlisting}[label={lst:shareimpl},%
  81         caption={Base share implementation}]
  82 realDeviceStore :: Shared [MTaskDevice]
  83 realDeviceStore = memoryShare "mTaskDevices" []
  84
  85 deviceStore :: RWShared (Maybe (MTaskDevice, Int)) [MTaskDevice] [MTaskDevice]
  86 deviceStore = SDSSource {SDSSource | name="deviceStore", read=realRead, write=realWrite}
  87 where
  88         realRead :: (Maybe (MTaskDevice,Int)) *IWorld -> (MaybeError TaskException [MTaskDevice], *IWorld)
  89         realRead p iw = read realDeviceStore iw
  90
  91         realWrite :: (Maybe (MTaskDevice,Int)) [MTaskDevice] *IWorld
  92                         -> (MaybeError TaskException (SDSNotifyPred (Maybe (MTaskDevice,Int))), *IWorld)
  93         realWrite mi w iw
  94         # (merr, iw) = write w realDeviceStore iw
  95         | isError merr || isNothing mi = (merr $> notifyPred mi, iw)
  96         # (Just (dev, ident)) = mi
  97         | ident == -1 = (merr $> notifyPred mi, iw)
  98         = case find ((==)dev) w of
  99                 Nothing = (Error $ exception "Device doesn't exist anymore", iw)
 100                 Just {deviceShares} = case find (\d->d.identifier == ident) deviceShares of
 101                         Nothing = (Error $ exception $ "deviceStore: Share doesn't exist: " +++ toString ident, iw)
 102                         Just s = case sendMessagesIW [MTUpd ident s.MTaskShare.value] dev iw of
 103                                 (Error e, iw) = (Error e, iw)
 104                                 (Ok _, iw) = (Ok $ notifyPred mi, iw)
 105
 106         notifyPred :: (Maybe (MTaskDevice, Int)) (Maybe (MTaskDevice, Int)) -> Bool
 107         notifyPred Nothing Nothing = True
 108         notifyPred Nothing (Just _) = False
 109         notifyPred (Just _) Nothing = False
 110         notifyPred (Just (d1, -1)) (Just (d2, _)) = d1 == d2
 111         notifyPred (Just (d1, i1)) (Just (d2, i2)) = d1 == d2 && i1 == i2
 112 \end{lstlisting}