conclusion.discussion.tex

   1 The system is still a crude prototype and a proof of concept. Improvements and
   2 extension for the system are amply available in several fields of study.
   3
   4 \subsection{Simulation}
   5 An additional simulation view to the \gls{mTask}-\gls{EDSL} could be added that
   6 works in the same way as the existing \gls{C}-backed simulation. It simulates
   7 the bytecode interpretation. Moreover, it would also be possible to let the
   8 simulator function as a real device, thus handling all communication through
   9 the existing \gls{SDS}-based systems. At the moment the \emph{POSIX}-client is
  10 the reference client and contains debugging code.  Adding a simulation view to
  11 the system allows for easy interactive debugging.  However, it might not be
  12 easy to devise a simulation tool that accurately simulates the \gls{mTask}
  13 system on some levels. The semantics can be simulated but timing and peripheral
  14 input/output are more difficult to simulate properly.
  15
  16 \subsection{Optimization}
  17 \paragraph{Multitasking on the client:}
  18 True multitasking could be added to the client software. This allows
  19 \gls{mTask}-\glspl{Task} to run truly parallel. All \gls{mTask}-\glspl{Task}
  20 get slices of execution time and will each have their own interpreter state
  21 instead of a single system-wide state which is reset after am \gls{mTask}
  22 finishes. This does require separate stacks for each \gls{Task} and therefore
  23 increases the system requirements of the client software. However, it could be
  24 implemented as a compile-time option and exchanged during the handshake so that
  25 the server knows the multithreading capabilities of the client. Multithreading
  26 allows \glspl{Task} to be truly interruptible by other \glspl{Task}.
  27 Furthermore, this allows for more fine-grained timing control of \glspl{Task}.
  28
  29 \paragraph{Optimizing the interpreter:}
  30 Due to time constraints and focus, hardly any work has been done in the
  31 interpreter. The current interpreter is a no nonsense stack machine. A lot of
  32 improvements can be done in this part. For example, precomputed \emph{gotos}
  33 can improve jumping to the correct part of the code corresponding to the
  34 correct instruction.  Moreover, the stack currently consists of 16-bit values.
  35 All operations work on 16-bit values and this simplifies the interpreter
  36 implementation. A memory improvement can be made by converting the stack to
  37 8-bit values. This does pose some problems since an equality instruction must
  38 work on single-byte booleans \emph{and} two-byte integers. Adding specialized
  39 instructions per word size could overcome this problem.
  40
  41 \subsection{Resources}
  42 \paragraph{Resource analysis: }
  43 Resource analysis during compilation can be useful to determine if an
  44 \gls{mTask}-\gls{Task} is suitable for a specific device. If the device does
  45 not contain the correct peripherals --- such as an \gls{LCD} --- then the
  46 \gls{mTask}-\gls{Task} should be rejected and feedback to the user must be
  47 given. It might even be possible to do this statically on the type level. The
  48 current system does not have any of this built-in. Sending a \gls{Task} that
  49 uses the \gls{LCD} to a device not containing one will result in the device
  50 just skipping the \gls{LCD} related instructions.
  51
  52 \paragraph{Extended resource analysis: }
  53 The previous idea could be extended to the analysis of stack size and possibly
  54 communication bandwidth. With this functionality ever more reliable fail-over
  55 systems can be designed. When the system knows precise bounds it can allocate
  56 more \glspl{Task} on a device whilst staying within safe memory bounds. The
  57 resource allocation can be done at runtime within the backend itself or a
  58 general backend can be devised that can calculate the resources needed for a
  59 given \gls{mTask}. A specific \gls{mTask} cannot have multiple views at the
  60 same time due to the restrictions of class based shallow embedding. It might
  61 even be possible to encode the resource allocation in the type system itself
  62 using forms of dependant types.
  63
  64 \subsection{Functionality}
  65 \paragraph{Add more combinators: }
  66 More \gls{Task}-combinators --- already existing in the \gls{iTasks}-system ---
  67 could be added to the \gls{mTask}-system to allow for more fine-grained control
  68 flow between \gls{mTask}-\glspl{Task}. In this way the new system follows the
  69 \gls{TOP} paradigm even more and makes programming \gls{mTask}-\glspl{Task} for
  70 \gls{TOP}-programmers more seamless. Some of the combinators require previously
  71 mentioned extension such as the parallel combinator. Others might be achieved
  72 using simple syntactic transformations.
  73
  74 \paragraph{Launch \glspl{Task} from a \gls{Task}:}
  75 Currently the \gls{C}-view allows \glspl{Task} to launch other \glspl{Task}. In
  76 the current system this type of logic has to take place on the server side.
  77 Adding this functionality to the bytecode-view allows greater flexibility,
  78 easier programming and less communication resources. Adding these semantics
  79 requires modifications to the client software and extensions to the
  80 communication protocol since relations between \glspl{Task} also need to be
  81 encoded and communicated.
  82
  83 The \gls{SDS} functionality in the current system is bare. There is no easy way
  84 of reusing an \gls{SDS} for another \gls{Task} on the same device or on another
  85 device. Such functionality can be implemented in a crude way by tying the
  86 \glspl{SDS} together in the \gls{iTasks} environment. However, this will result
  87 in a slow updating system. Functionality for reusing shares from a device
  88 should be added. This requires rethinking the storage because some typedness is
  89 lost when the \gls{SDS} is stored after compilation. A possibility would be to
  90 use runtime typing with \CI{Dynamic}s or the encoding technique currently used
  91 for \CI{BCValue}s. Using \glspl{SDS} for multiple \glspl{Task} within one
  92 device is solved when the previous point is implemented.
  93
  94 Another way of improving on \gls{SDS} handling is to separate \glspl{SDS} from
  95 devices. In this implementation, the \gls{SDS} not only needs to know on which
  96 device it is, but also which internal device \gls{SDS} id it has. A pro of
  97 this technique is that the \gls{SDS} can be shared between \glspl{Task} that
  98 are not defined in the same scope because they are separated. A con of this
  99 implementation is that the mechanisms for implementing \glspl{SDS} have to be
 100 more complex, they have to keep track of the devices containing or sharing an
 101 \gls{SDS}. Moreover, when the \gls{SDS} is updated, all attached devices must
 102 be updated which requires some extra work.
 103
 104 \subsection{Robustness}
 105 \paragraph{Reconnect with lost devices:}
 106 The robustness of the system can be greatly improved. Devices that lose
 107 connection are not well supported in the current system. The device will stop
 108 functioning and has to be emptied for a reconnect. \Glspl{Task} residing on a
 109 device that disconnected should be kept on the server to allow a swift
 110 reconnect and restoration of the \glspl{Task}. This holds the same for the
 111 client software. The client drops all existing \glspl{Task} on a shutdown
 112 request. An extra specialization of the shutdown could be added that drops the
 113 connection but keeps the \glspl{Task} in memory. During the downtime the
 114 \glspl{Task} can still be executed but publications need to be delayed. If the
 115 same server connects to the client the delayed publications can be sent
 116 anyways.
 117
 118 \paragraph{Reverse \gls{Task} sending:}
 119 Furthermore, devices could send their current \glspl{Task} back to the
 120 server to synchronize it. This allows interchanging servers without
 121 interrupting the client. Allowing the client to send \glspl{Task} to the server
 122 is something to handle with care because it can easily cause high bandwidth
 123 usage.