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..2020  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/>.

'/

/'### INTRO ##################################################################'/

@startuml

title **µRtWare**\nurtSubscriberFetchLatestMessage()\n

!include ../../functions.iuml

/'### PARAMETERS & START #####################################################'/

start

note

  -- ""**subscriber** : urt_subscriber_t*"" --

  The subscriber that shall fetch the message.

  Must not be ""NULL"".

  -- ""**payload** : void*"" --

  Pointer where to copy the payload to.

  May be ""NULL"" for messages without payload.

  -- ""**bytes** : size_t"" --

  Payload size in bytes.

  -- ""**latency** : urt_delay_t*"" --

  The latency can be returned by reference.

  May be ""NULL"".

end note

/'### PROCEDURE ##############################################################'/

:lock topic;

if (Is HRT subscriber?) then (yes)

  :lock next message;

else (no)

  if (Has a message been read before?) then (yes)

    :lock last read message;

    if (Message timestamp equals local copy?) then (yes)

    else (no)

      partition "find oldest valid message" {

        :lock next message;

        note: Locked two messages ahead.

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

          fork

            :unlock current message;

          fork again

            :lock one message further ahead;

          endfork

        endwhile (no)

        :unlock next message;

        note: One message still locked.

      }

    endif

  else (no)

    :lock message after topic's latest message;

  endif

endif

partition "iterate to latest" {

  :lock one message further ahead;

  note: Locked two messages ahead.

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

    fork

      if (Is HRT subscriber?) then (yes)

        fork

          :decrement HRT counter of current message;

        fork again

          :update QoS delay timer (@subscriber);

        endfork

      else (no)

      endif

      :unlock current message;

    fork again

      :lock one message further ahead;

    endfork

  endwhile (no)

  :unlock next message;

  note: One message still locked.

}

fork

  :set last fetched message pointer to locked message;

fork again

  fork

    :copy timestamp of message;

  fork again

    if (Optional output argument "latency" given?) then (yes)

      :set latency value (now - message origin time);

    else (no)

    endif

  endfork

fork again

  :copy message payload;

fork again

  if (Is HRT subscriber?) then (yes)

    fork

      :decrement HRT counter of current message;

      if (At least one HRT counter became 0?) then (yes)

        :signal topic's condition variable;

      else (no)

      endif

    fork again

      :update QoS delay timer (@subscriber);

    endfork

  else (no)

  endif

endfork

:unlock message;

:unlock topic;

/'### STOP & RETURN ##########################################################'/

stop

note

  -- **return** ""urt_status_t"" --

  Returns ""URT_STATUS_OK"".

end note

/'### OUTRO ##################################################################'/

@enduml