spark-shell启动分析

spark-shell脚本源码

#!/usr/bin/env bash

#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

#
# Shell script for starting the Spark Shell REPL

cygwin=false
case "$(uname)" in
  CYGWIN*) cygwin=true;;
esac

# Enter posix mode for bash
set -o posix

if [ -z "${SPARK_HOME}" ]; then
  source "$(dirname "$0")"/find-spark-home
fi

export _SPARK_CMD_USAGE="Usage: ./bin/spark-shell [options]

Scala REPL options:
  -I                    preload , enforcing line-by-line interpretation"

# SPARK-4161: scala does not assume use of the java classpath,
# so we need to add the "-Dscala.usejavacp=true" flag manually. We
# do this specifically for the Spark shell because the scala REPL
# has its own class loader, and any additional classpath specified
# through spark.driver.extraClassPath is not automatically propagated.
SPARK_SUBMIT_OPTS="$SPARK_SUBMIT_OPTS -Dscala.usejavacp=true"

function main() {
  if $cygwin; then
    # Workaround for issue involving JLine and Cygwin
    # (see http://sourceforge.net/p/jline/bugs/40/).
    # If you're using the Mintty terminal emulator in Cygwin, may need to set the
    # "Backspace sends ^H" setting in "Keys" section of the Mintty options
    # (see https://github.com/sbt/sbt/issues/562).
    stty -icanon min 1 -echo > /dev/null 2>&1
    export SPARK_SUBMIT_OPTS="$SPARK_SUBMIT_OPTS -Djline.terminal=unix"
    "${SPARK_HOME}"/bin/spark-submit --class org.apache.spark.repl.Main --name "Spark shell" "$@"
    stty icanon echo > /dev/null 2>&1
  else
    export SPARK_SUBMIT_OPTS
    "${SPARK_HOME}"/bin/spark-submit --class org.apache.spark.repl.Main --name "Spark shell" "$@"
  fi
}

# Copy restore-TTY-on-exit functions from Scala script so spark-shell exits properly even in
# binary distribution of Spark where Scala is not installed
exit_status=127
saved_stty=""

# restore stty settings (echo in particular)
function restoreSttySettings() {
  stty $saved_stty
  saved_stty=""
}

function onExit() {
  if [[ "$saved_stty" != "" ]]; then
    restoreSttySettings
  fi
  exit $exit_status
}

# to reenable echo if we are interrupted before completing.
trap onExit INT

# save terminal settings
saved_stty=$(stty -g 2>/dev/null)
# clear on error so we don't later try to restore them
if [[ ! $? ]]; then
  saved_stty=""
fi

main "$@"

# record the exit status lest it be overwritten:
# then reenable echo and propagate the code.
exit_status=$?
onExit

1. cygwin=false
   windows操作linux系统需要安装这个，初始值为false。

2. shell的uname命令，返回当前系统信息。

   uname用法：
   -a或–all：显示全部的信息；
   -m或–machine：显示电脑类型；
   -n或-nodename：显示在网络上的主机名称；
   -r或–release：显示操作系统的发行编号；
   -s或–sysname：显示操作系统名称；
   -v：显示操作系统的版本；
   -p或–processor：输出处理器类型或"unknown"；
   -i或–hardware-platform：输出硬件平台或"unknown"；
   -o或–operating-system：输出操作系统名称；
   –help：显示帮助；
   –version：显示版本信息。

3. shell的case用法。

   case $变量名 in
   	模式一）
   		command
   	;;
   	模式二）
   		command
   	;;
   	*）
   		command
   	;;
   esac
   
   例：
   read -p 'press key:' KEY
   case $KEY in 
   	[a-z][A-Z])
   	echo 'a leeter';;
   	[0-9])
   	echo 'a digit';;
   	*)
   	echo 'other';;
   esac
   

4. if [ -z “${SPARK_HOME}” ];
   表示${SPARK_HOME}长度为零则为真。

5. dirname “$0”
   表示当前运行命令的路径，其中 $0 返回当前运行的命令。

6. 从脚本中看出执行及调用流程：
   spark-shell(main) → spark-submit → spark-class → org.apache.spark.launcher.Main "$@"
   其实，spark-shell里面调用的还是spark-submit，一直追溯下去，会发现底层就是使用了java来启动。

7. REPL：Read-Eval-Print-Loop