AMiRo-OS

/'

µRtWare is a lightweight publish/subscribe middleware for real-time

applications. It was developed as part of the software habitat for the

Autonomous Mini Robot [1] (AMiRo) but can be used for other purposes as well.

Copyright (C) 2018..2019  Thomas Schöpping et al.

This program is free software: you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation, either version 3 of the License, or

(at your option) any later version.

This program is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

GNU General Public License for more details.

You should have received a copy of the GNU General Public License

along with this program.  If not, see <http://www.gnu.org/licenses/>.

'/

@startuml

title **µRtWare**\nurtSubscriberFetchMessage()\n

start

note

  event received

endnote

:lock topic;

note

  The message list is part of the topic and must be locked.

endnote

if (Is HRT subscriber?) then (yes)

  :lock next message;

  if (Fetch next or latest message?) then (next)

  else (latest)

    partition "iterate to latest" {

      :lock next message;

      note

        locked two messaged ahead

      endnote

      while (Timestamp of next message is younger than current?) is (yes)

        fork

          fork

            :decremenet HRT counter of current message;

          fork again

            :update QoS delay timer (@subscriber);

            note

              no lock required since this timer is only accessed when the topic is locked

            endnote

          endfork

          :unlock current message;

        fork again

          :lock next message;

        endfork

      endwhile (no)

      :unlock next message;

      note

        one message ahead still locked

        but HRT counter not yet decremented

      endnote

    }

  endif

  fork

    :decrement HRT counter of current message;

  fork again

    :update QoS delay timer (@subscriber);

    note

      no lock required since this timer is only accessed when the topic is locked

    endnote

  endfork

else (no)

  :lock last read message;

  if (Timestamp equals local copy?) then (yes)

  else (no)

    partition "find oldest valid message" {

      :lock next message;

      while (Timestamp of next is younger then of current?) is (yes)

        fork

          :unlock current mesage;

        fork again

          :lock one message further ahaead;

        endfork

      endwhile (no)

      :unlock next message;

    }

  endif

  if (Fetch next or latest message?) then (next)

  else (latest)

    partition "iterate to latest" {

      :lock next message;

      while (Timestamp of next message is younger then current?) is (yes)

        fork

          :unlock current message;

        fork again

          :lock next message;

        endfork

      endwhile (no)

      :unlock next message;

      note

        one message ahead still locked

      endnote

    }

  endif

endif

fork

  :set last fetched message pointer to locked message;

fork again

  :copy timestamp of message;

fork again

  if (Copy of payload requested?) then (yes)

    :copy message payload;

  else (no)

  endif

endfork

:unlock message;

:unlock topic;

stop

@enduml