BackgroundProcess

#!/usr/bin/bash
# Written by Manuel Iglesias. [email protected]

readonly CommandName=${0##*/}
readonly CommandOptionString="-c"
readonly RunInBackgroundOptionString="-b"
readonly KillProcessOptionString="-k"
readonly ProcessFinishedOptionString="-f"
readonly TempDir="/tmp"
readonly KillProcessTimeoutSeconds="1" # Max time for killed process's parent to save child process' info. '$CommandName -k ' fails if parent running after timeout.
readonly KillSignal="TERM"
readonly CommandLineVarName="CommandLine"   # Process info output.
readonly ElapsedTime_mSVarName="ElapsedTime_mS" # Process info output.
readonly ExitCodeVarName="ExitCode"     # Process info output.
readonly StandardOutVarName="StandardOut"   # Process info output.
readonly StandardErrorVarName="StandardError"   # Process info output.



Usage() {
echo -e "'${CommandName}' can be used to launch/control a process running in background.
Usage: '$CommandName $CommandOptionString Command [Param [Param...]]'.
  Launches 'Command [Param [Param...]]' in background and outputs its Pid.
  Exitcode 0 if successful.
Usage: '$CommandName Pid'.
  Outputs background process' information (see below).
  Exitcode 0 if 'Pid' is valid and process no longer running (information valid).
  Exitcode 1 if 'Pid' valid and process still running (information not valid).
  Exitcode non 0 if 'Pid' not valid or any other problem (information not valid).
Usage: '$CommandName $ProcessFinishedOptionString Pid'.
  Checks if process with 'Pid' is running. Does not output any process information.
  Exitcode 0 if 'Pid' is valid and the process is no longer running
  Exitcode 1 if 'Pid' valid and the process is still running.
  Exitcode non 0 if 'Pid' not valid or any other problem.
Usage: '$CommandName $KillProcessOptionString Pid'.
  Kills process with 'Pid' (previously launched by '${CommandName}').
  Outputs background process' information (see below).
  Exitcode 0 if 'Pid' is valid and was killed successfully (or had exited already)
    and if the process' information was read successfully.
Background process' information:
  Text that, when parsed, provides the following variables and values:
    '${CommandLineVarName}': Command and parameters of process when launched.
    '${ElapsedTime_mSVarName}': Process' running time (milliSeconds).
    '${ExitCodeVarName}': Process' exit code.
    '$StandardOutVarName': StdOut generated by process while running.
    '${StandardErrorVarName}': StdErr generated by process while running.
  See System_Docs/System/BashCodeRepository/'Background processes' (parsing).
Normal usage sequence:
 -Use '$CommandName $CommandOptionString Command ...' to launch a process and get its Pid.
 -Do other tasks.
 -Use '${CommandName} $ProcessFinishedOptionString Pid' to check if the background process has exited.
 -Use '${CommandName} Pid' to read the process' information when it has exited.
 -Parse the background process' information and use Variables' contents.
 -If the background process has not exited in the allotted time, kill it with
    '$CommandName $KillProcessOptionString Pid' (and get the killed process' [partial] information)." 1>&2
return 0
}



CommandOption=false;RunInBackgroundOption=false;KillProcessOption=false;ProcessFinishedOption=false
if [[ "$1" == "$CommandOptionString" ]]
  then
    CommandOption=true
    shift
  else
    if [[ "$1" == "$RunInBackgroundOptionString" ]]
      then
        RunInBackgroundOption=true
        shift
      else
        if [[ "$1" == "$KillProcessOptionString" ]]
          then
            KillProcessOption=true
            shift
          else
            if [[ "$1" == "$ProcessFinishedOptionString" ]]
              then
                ProcessFinishedOption=true
                shift
            fi
        fi
    fi
fi

if [[ $# -lt 1 || "$1" == "-h" || "$1" == "-?" || "$1" == "--help" || "$1" == "-help" ]]
  then
    Usage
    exit 64
fi

if $CommandOption
  then
    if ! type "$1" &>/dev/null
      then
        echo -e "${CommandName}: Command '${1}' not in '\$PATH'. Aborting!" 1>&2
        exit 127
    fi
#   'coproc': Equivalent to ending command with '&'. '&' does not work if shell invoked with `` (ProcessId=`BackgroundProcess -c Command`).
#   &>/dev/null so that no error message is given when killed. Also to allow background processes to be launched from this background process (pipes?).
    if coproc $CommandName $RunInBackgroundOptionString "$@" &>/dev/null
      then
        eval "exec ${COPROC[0]}>&-" # Close coproc stdout pipe (See Books/Science/Computer_Science/Linux/Bash_scripting/Bash_Co_Processes).
        eval "exec ${COPROC[1]}<&-" # Close coproc stdin pipe (See Books/Science/Computer_Science/Linux/Bash_scripting/Bash_Co_Processes).
        echo "$!"
        exit 0
      else
        echo -e "${CommandName}: Launching in background with 'coproc' failed with ExitCode: ${?}. Aborting!" 1>&2 # Should never happen but... just in case ;-).
        exit 70
    fi
fi

if $RunInBackgroundOption
  then
    TempFile="${TempDir}/${CommandName}_$$"
    TempErrorFile="${TempFile}.Error"
    >$TempErrorFile         # So that other users can not read file.
    chmod 600 $TempErrorFile        # So that other users can not read file.
    TempOutFile="${TempFile}.Out"
    >$TempOutFile           # So that other users can not read file.
    chmod 600 $TempOutFile      # So that other users can not read file.
    cd $TempDir # So that child process uses it as working directory (And does not tie up current wd).
    exec 0<&- # Close stdin.
    exec 1>&- # Close stdout.
    exec 2>&- # Close stderr.
    StartTime=$(date +%s.%N) # Seconds.Nanoseconds since 1970−01−01.
    Decimals=${StartTime##*\.}          # Fast Times1000.
    Decimals=${Decimals:0:3}            # Fast Times1000.
    StartTime="${StartTime%\.*}$Decimals"   # Fast Times1000.
    1>$TempOutFile 2>$TempErrorFile "$@"
    ExitCode=$?
    EndTime=$(date +%s.%N) # Seconds.Nanoseconds since 1970−01−01.
    Decimals=${EndTime##*\.}            # Fast Times1000.
    Decimals=${Decimals:0:3}            # Fast Times1000.
    EndTime="${EndTime%\.*}$Decimals"       # Fast Times1000.
    ((ElapsedTime_mS = EndTime - StartTime))
    echo -e "${CommandLineVarName}=\"$@\"
#
${ElapsedTime_mSVarName}=${ElapsedTime_mS}
#
${ExitCodeVarName}=${ExitCode}
#
${StandardOutVarName}=\"$(< ${TempOutFile})\"
#
${StandardErrorVarName}=\"$(< ${TempErrorFile})\"
#" >$TempFile
    chmod 600 $TempFile # So that other users can not read file.
    rm -f $TempErrorFile $TempOutFile
    exit 0
fi

if [[ $# -ne 1 ]]
  then
    Usage
    exit 64
fi

TempFile="${TempDir}/${CommandName}_$1"

if ProcessCommandName=$(2>/dev/null ps --pid=$1 h -o comm)
  then
    if [[ "$CommandName" == "${ProcessCommandName}${CommandName#${ProcessCommandName}}" ]] # 'ps' returns only the 15 first characters of command.
      then
        if $KillProcessOption
          then
            for Child in $(ps -o pid --no-headers --ppid $1)
              do
                pkill -${KillSignal} -P $Child &>/dev/null # Kill BackgroundProcess' Child's children (grandchildren).
              done
            pkill -${KillSignal} -P $1 &>/dev/null # -P means kill processes whose parent process ID is listed. Here: kill BackgroundProcess' children.
            ((Timeout = KillProcessTimeoutSeconds * 10)) # Will be checked every 1/10 seconds.
            while &>/dev/null ps --pid=$1 && [[ $Timeout -gt 0 ]]
              do
                sleep 0.1
                ((Timeout--))
              done
            if &>/dev/null ps --pid=$1
              then
                echo -e "${CommandName}: Warning! Process '${1}' could not be killed." 1>&2
                exit 70
              else
                if [[ -f $TempFile ]]
                  then
                    cat $TempFile
                    rm -f $TempFile
                    exit 0
                  else
                    echo -e "${CommandName}: Process killed but temporary file not found. No record of process '${1}'." 1>&2
                    exit 70
                fi
            fi
        fi
        echo -e "${CommandName}: Process '${1}' still running." 1>&2
        exit 1
      else
        echo -e "${CommandName}: Process '${1}' running but not an instance of '${CommandName}'. Aborting." 1>&2
        exit 70
    fi
fi

if [[ -f $TempFile ]]
  then
    if $ProcessFinishedOption
      then
        exit 0
    fi
    if $KillProcessOption
      then
        echo -e "${CommandName}: Process '${1}' has already exited. Kill request ignored." 1>&2
    fi
    cat $TempFile
    rm -f $TempFile
  else
    echo -e "${CommandName}: Process not running and temporary file not found. No record of process '${1}'." 1>&2
    exit 70
fi