doc(bkgpslog):Add note to simplify main loop

[EVA-2020-02.git] / exec / bkgpslog-plan.org

* bkgpslog task list
** DONE Add job control for short buffer length
   CLOSED: [2020-07-02 Thu 16:04]
2020-07-02T14:56Z; bktei> File write operations were bundled into a
magicWriteBuffer function that is called then detached from the script
shell (job control), but the detached job is not tracked by the main
script. A problem may arise if two instances of magicWriteBuffer
attempt to write to the same tar simultaneously. Two instances of
magicWriteBuffer may exist if the buffer length is low (ex: 1 second);
the default buffer length of 60 seconds should reduce the probability
of a collision but it should be possible for the main script to track
the process ID of a magicWriteBuffer() as soon as it detaches and then
checking (via ~$!~ as described [[https://bashitout.com/2013/05/18/Ampersands-on-the-command-line.html][here]]) that the process is still alive.
2020-07-02T15:23Z; bktei> I found that the Bash ~wait~ built-in can be
used to delay processing until a specified job completes. The ~wait~
command will pause script execution until all backgrounded processes
complete.
2020-07-02T16:03Z; bktei> Added ~wait~.
** DONE Rewrite tar initialization function
   CLOSED: [2020-07-02 Thu 17:23]
2020-07-02T17:23Z; bktei> Simplify tar initialization function so
VERSION file is used to test appendability of tar as well as to mark
when a new session is started.
** DONE Consolidate tar checking/creation into function
   CLOSED: [2020-07-02 Thu 18:33]
2020-07-02T18:33Z; bktei> Simplify how the output tar file's existence
is checked and its status as a valid tar file is validated. This was
done using a new function ~checkMakeTar~.
** DONE Add VERSION if output tar deleted between writes

   CLOSED: [2020-07-02 Thu 20:22]
2020-07-02T20:21Z; bktei> Added bkgpslog-specified function
magicWriteVersion() to be called whenever a new time-stamped ~VERSION~
file needs to be generated and appended to the output tar file
~PATHOUT_TAR~.
** TODO Rewrite buffer loop to reduce lag between gpspipe runs
2020-07-03T17:10Z; bktei> As is, there is still a 5-6 second lag
between when ~gpspipe~ times out at the end of a buffer round and when
~gpspipe~ is called by the subsequent buffer round. I believe this can
be reduced by moving variable manipulations inside the
asynchronously-executed magicWriteBuffer() function. Ideally, the
while loop should look like:

#+BEGIN_EXAMPLE
while( $SECONDS < $SCRIPT_TTL); do
    gpspipe-r > "$DIR_TMP"/buffer.nmea
    writeBuffer &
done
#+END_EXAMPLE

* bkgpslog narrative
** Initialize environment
*** Init variables
**** Save timeStart (YYYYmmddTHHMMSS±zz)
*** Define Functions
**** Define Debugging functions
**** Define Argument Processing function
**** Define Main function
** Run Main Function
*** Process Arguments
*** Set output encryption and compression option strings
*** Check that critical apps and dirs are available, displag missing ones.
*** Set lifespans of script and buffer
*** Init temp working dir ~DIR_TMP~
Make temporary dir in tmpfs dir: ~/dev/shm/$(nonce)..bkgpslog/~ (~DIR_TMP~)
*** Initialize ~tar~ archive
**** Write ~bkgpslog~ version to ~$DIR_TMP/VERSION~
**** Create empty ~tar~ archive in ~DIR_OUT~ at ~PATHOUT_TAR~

Set output file name to:
: PATHOUT_TAR="$DIR_OUT/YYYYmmdd..hostname_location.gz.age.tar"
Usage: ~iso8601Period $timeStart $timeEnd~ 

**** Append ~VERSION~ file to ~PATHOUT_TAR~

Append ~$DIR_TMP/VERSION~ to ~PATHOUT_TAR~ via ~tar --append~

*** Read/Write Loop (Record gps data until script lifespan ends)
**** Determine output file paths
**** Define GPS conversion commands
**** Fill Bash variable buffer from ~gpspipe~
**** Process bufferBash, save secured chunk set to ~DIR_TMP~
**** Append each secured chunk to ~PATHOUT_TAR~
: tar --append --directory=DIR_TMP --file=PATHOUT_TAR $(basename PATHOUT_{NMEA,GPX,KML} )
**** Remove secured chunk from ~DIR_TMP~