results.itasks.tex

   1 The server side of the system is written in \gls{iTasks}. Functions for
   2 managing devices, \glspl{Task} and \glspl{SDS} have been created to support the
   3 functionality. An interactive application has been created that allows an
   4 interactive management console for the \gls{mTask} system. This interface
   5 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  11 contain \glspl{Task}, \glspl{SDS} or errors that are no longer applicable in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 needs to keep track of the \glspl{SDS} stored on
  43 the client. \glspl{SDS} can be stored on only one device at the same time.
  44 that also stores the of devices. This means that if a \gls{SDS} updates,
  45 everyone watching it will be notified. This would result in to a lot of
  46 notifications that are not ment to be for the listener. Moreover, when a client
  47 updates the \gls{SDS} this is processed by the connection handler and results
  48 in an update of the real \gls{SDS}.
  49 Finally, the \gls{SDS} of a client must be synchronized with the actual device.
  50 There are several ways of tackling this problem each with their own pros and
  51 cons and their own level of abstraction.
  52
  53 \begin{itemize}
  54         \item Instantiate an actual \gls{iTasks}-\gls{SDS} for every \gls{SDS} used
  55                 in a client.
  56
  57
  58         \item Instantiate a \gls{iTasks}-\gls{SDS} for every device that stores all
  59                 their \glspl{SDS}.
  60
  61         \item Use only one \gls{iTasks}-\gls{SDS} for all devices.
  62 \end{itemize}
  63
  64 \begin{lstlisting}[label={lst:actualdev},%
  65         caption={Real types for the device \gls{SDS}}]
  66 deviceStoreNP :: Shared [MTaskDevice]
  67 deviceStore :: RWShared (Maybe (MTaskDevice, Int)) [MTaskDevice] [MTaskDevice]
  68 \end{lstlisting}
  69
  70 \subsection{Parametric Lens}
  71 The type of the parametric lens is \CI{Maybe (MTaskDevice, Int)}. The \gls{SDS}
  72 can either be focussed on the entire share, from now on global. Moreover, the
  73 \gls{SDS} can focus on a single device, from now on local. A local \gls{SDS}
  74 can also specifically focus on a single \gls{SDS} on a single device.
  75
  76 The implementation for the share is shown in Listing~\ref{lst:shareimpl}. The
  77 \CI{realDeviceStore} \gls{SDS} is not exported through the header files. This
  78 \gls{SDS} contains the actual \gls{SDS} that writes to disk or memory.
  79 \CI{Int} is the identifier of the \gls{SDS}. The \gls{iTasks} way of applying
  80 lenses is through the \CI{sdsFocus} function and through the \CI{sdsLens}
  81 functions. \CI{sdsFocus} allows the programmer to fix the parameter.
  82 \CI{sdsLens} is basically a \CI{mapReadWrite} that has access to the parameter.
  83 This allows the programmer to create filters and lenses. Both of the methods
  84 are not good enough for the device \gls{SDS} because they do not achieve the
  85 writing to the actual device. Writing to a device requires being able to write
  86 to \glspl{SDS}. To solve this problem, a real base \gls{SDS} is created. All
  87 the details are visible in Listing~\ref{shareimpl}.
  88 \todo{elaborate}
  89
  90 \begin{lstlisting}[label={lst:shareimpl},%
  91         caption={Base share implementation}]
  92 realDeviceStore :: Shared [MTaskDevice]
  93 realDeviceStore = memoryShare "mTaskDevices" []
  94
  95 deviceStore :: RWShared (Maybe (MTaskDevice, Int)) [MTaskDevice] [MTaskDevice]
  96 deviceStore = SDSSource {SDSSource | name="deviceStore", read=realRead, write=realWrite}
  97 where
  98         realRead :: (Maybe (MTaskDevice,Int)) *IWorld -> (MaybeError TaskException [MTaskDevice], *IWorld)
  99         realRead p iw = read realDeviceStore iw
 100
 101         realWrite :: (Maybe (MTaskDevice,Int)) [MTaskDevice] *IWorld
 102                         -> (MaybeError TaskException (SDSNotifyPred (Maybe (MTaskDevice,Int))), *IWorld)
 103         realWrite mi w iw
 104         # (merr, iw) = write w realDeviceStore iw
 105         | isError merr || isNothing mi = (merr $> notifyPred mi, iw)
 106         # (Just (dev, ident)) = mi
 107         | ident == -1 = (merr $> notifyPred mi, iw)
 108         = case find ((==)dev) w of
 109                 Nothing = (Error $ exception "Device doesn't exist anymore", iw)
 110                 Just {deviceShares} = case find (\d->d.identifier == ident) deviceShares of
 111                         Nothing = (Error $ exception $ "deviceStore: Share doesn't exist: " +++ toString ident, iw)
 112                         Just s = case sendMessagesIW [MTUpd ident s.MTaskShare.value] dev iw of
 113                                 (Error e, iw) = (Error e, iw)
 114                                 (Ok _, iw) = (Ok $ notifyPred mi, iw)
 115
 116         notifyPred :: (Maybe (MTaskDevice, Int)) (Maybe (MTaskDevice, Int)) -> Bool
 117         notifyPred Nothing Nothing = True
 118         notifyPred Nothing (Just _) = False
 119         notifyPred (Just _) Nothing = False
 120         notifyPred (Just (d1, -1)) (Just (d2, _)) = d1 == d2
 121         notifyPred (Just (d1, i1)) (Just (d2, i2)) = d1 == d2 && i1 == i2
 122 \end{lstlisting}