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/'
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µRtWare is a lightweight publish/subscribe middleware for real-time
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applications. It was developed as part of the software habitat for the
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Autonomous Mini Robot [1] (AMiRo) but can be used for other purposes as well.
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Copyright (C) 2018..2020  Thomas Schöpping et al.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program.  If not, see <http://www.gnu.org/licenses/>.
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'/
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/'### INTRO ##################################################################'/
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@startuml
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title **µRtWare**\nurtHrtSubscriberFetchNextMessage()\n
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!include ./functions.iuml
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/'### PARAMETERS & RETURN ####################################################'/
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note
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  -- **subscriber** : urt_hrtsubscriber_t* --
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  The HRT subscriber that shall fetch the message.
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  Must not be ""NULL"".
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  -- **payload** : void* --
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  Pointer where to copy the payload to.
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  May be ""NULL"" for messages without payload.
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  -- **bytes** : size_t --
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  Payload size in bytes.
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  -- **latency** : urt_delay_t* --
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  The latency can be returned by reference.
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  May be ""NULL"".
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  ====
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  -- **return** : urt_status_t --
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  Returns ""URT_STATUS_OK"" on success.
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  Returns ""URT_STATUS_ERROR"" if the subscriber is not associated to a topic.
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endnote
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/'### PROCEDURE ##############################################################'/
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start
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if (Associated to a topic?) then (yes)
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  :lock topic;
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  :proceed to next message;
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  fork
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    $fetch_message()
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  fork again
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    :decrement message's HRT counter;
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    if (HRT counter became 0?) then (yes)
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    else (no)
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      :signal topic's condition variable;
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    endif
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  fork again
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    if (Timestamp of next message is younger?) then (yes)
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      :update QoS delay timer wrt. next message;
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    else (no)
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    endif
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  endfork
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  :unlock topic;
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  stop
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  note
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    Returns ""URT_STATUS_OK"".
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  endnote
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else (no)
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  stop
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  note
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    Returns ""URT_STATUS_ERROR"".
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  endnote
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endif
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/'### OUTRO ##################################################################'/
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@enduml