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**\nurtFrtSubscriberFetchNextMessage()\n

!include ../functions.iuml

/'### PARAMETERS & RETURN ####################################################'/

note

  -- **subscriber** : urt_frtsubscriber_t* --

  The FRT 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"".

  ====

  -- **return** : urt_status_t --

  Returns ""URT_STATUS_OK"" on success.

  Returns ""URT_STATUS_FETCH_NOTOPIC"" if the subscriber is not associated to a topic.

  Retruns ""URT_STATUS_FETCH_NOMESSAGE"" if there is no new message to fetch.

  Returns ""URT_STATUS_JITTERVIOLATION"" if the message's latency violated the maximum expected jitter.

endnote

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

start

if (Associated to a topic?) then (yes)

  :lock topic;

  if (Timestamp of last read message equals local copy?) then (yes)

    if (Next message is younger?) then (yes)

      :proceed to next message;

    else (no)

      :unlock topic;

      stop

      note

        Returns ""URT_STATUS_FETCH_NOMESSAGE"".

      endnote

    endif

  else (no)

    partition "find oldest message" {

      repeat

        :proceed to next message;

      repeat while (Timestamp of next message is younger?) is (yes)

    }

  endif

  fork

    $fetch_message()

  fork again

    :calculate message latency;

    note

      Can be optimized in case all flags are disabled.

    endnote

    fork

      #EEEEEE:..//URT_CFG_PUBSUB_PROFILING == true//..\naccumulate ""sumLatencies"" value;

    fork again

      partition "//URT_CFG_PUBSUB_QOS_JITTERCHECKS == true || URT_CFG_PUBSUB_PROFILING == true//" #EEEEEE {

        if (Latency is lower than ""minLatency"" but within allowed jitter range?) then (yes)

          #EEEEEE:update ""minLatency"" value;

        elseif (Latency is greater than ""maxLatency"" but within allowed jitter range?) then (yes)

          #EEEEEE:update ""maxLatency"" value;

        else (no)

        endif

      }

    fork again

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

        :set ""latency"" value;

      else (no)

      endif

    endfork

  fork again

    partition "//URT_CFG_PUBSUB_PROFILING == true//" #EEEEEE {

      fork

        #EEEEEE:decrement counter of consumers left (@message);

      fork again

        #EEEEEE:increment counter of received messages;

      endfork

    }

  endfork

  :unlock topic;

  stop

  note

    Returns ""URT_STATUS_OK"" or ""URT_STATUS_JITTERVIOLATION"".

  endnote

else (no)

  stop

  note

    Returns ""URT_STATUS_FETCH_NOTOPIC"".

  endnote

endif

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

@enduml