# use POSIX interface, symlink is followed automatically
ZOOBIN="${BASH_SOURCE-$0}"
ZOOBIN="$(dirname "${ZOOBIN}")"
ZOOBINDIR="$(cd "${ZOOBIN}"; pwd)"
# 這裡會先配置一些必要的環境變數
if [ -e "$ZOOBIN/../libexec/zkEnv.sh" ]; then
  . "$ZOOBINDIR"/../libexec/zkEnv.sh
else
  . "$ZOOBINDIR"/zkEnv.sh
fi
#此處配置JMX，預設是開啟的，支援本地連線，如果遠端連線，需要單獨配置
# See the following page for extensive details on setting
# up the JVM to accept JMX remote management:
# http://java.sun.com/javase/6/docs/technotes/guides/management/agent.html
# by default we allow local JMX connections
if [ "x$JMXLOCALONLY" = "x" ]
then
    JMXLOCALONLY=false
fi

if [ "x$JMXDISABLE" = "x" ] || [ "$JMXDISABLE" = 'false' ]
then
#執行這裡
  echo "ZooKeeper JMX enabled by default" >&2
  if [ "x$JMXPORT" = "x" ]
  then
    # for some reason these two options are necessary on jdk6 on Ubuntu
    #   accord to the docs they are not necessary, but otw jconsole cannot
    #   do a local attach
#配置遠端連線，修改ZOOMAIN變數
    ZOOMAIN="-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.local.only=$JMXLOCALONLY org.apache.zookeeper.server.quorum.QuorumPeerMain"
  else
    if [ "x$JMXAUTH" = "x" ]
    then
      JMXAUTH=false
    fi
    if [ "x$JMXSSL" = "x" ]
    then
      JMXSSL=false
    fi
    if [ "x$JMXLOG4J" = "x" ]
    then
      JMXLOG4J=true
    fi
    echo "ZooKeeper remote JMX Port set to $JMXPORT" >&2
    echo "ZooKeeper remote JMX authenticate set to $JMXAUTH" >&2
    echo "ZooKeeper remote JMX ssl set to $JMXSSL" >&2
    echo "ZooKeeper remote JMX log4j set to $JMXLOG4J" >&2
    ZOOMAIN="-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=$JMXPORT -Dcom.sun.management.jmxremote.authenticate=$JMXAUTH -Dcom.sun.management.jmxremote.ssl=$JMXSSL -Dzookeeper.jmx.log4j.disable=$JMXLOG4J org.apache.zookeeper.server.quorum.QuorumPeerMain"
  fi
else
    echo "JMX disabled by user request" >&2
    ZOOMAIN="org.apache.zookeeper.server.quorum.QuorumPeerMain"
fi

if [ "x$SERVER_JVMFLAGS" != "x" ]
then
    JVMFLAGS="$SERVER_JVMFLAGS $JVMFLAGS"
fi

if [ "x$2" != "x" ]
then
    ZOOCFG="$ZOOCFGDIR/$2"
fi

# if we give a more complicated path to the config, don't screw around in $ZOOCFGDIR
if [ "x$(dirname "$ZOOCFG")" != "x$ZOOCFGDIR" ]
then
    ZOOCFG="$2"
fi

if $cygwin
then
    ZOOCFG=`cygpath -wp "$ZOOCFG"`
    # cygwin has a "kill" in the shell itself, gets confused
    KILL=/bin/kill
else
    KILL=kill
fi

echo "Using config: $ZOOCFG" >&2

case "$OSTYPE" in
*solaris*)
  GREP=/usr/xpg4/bin/grep
  ;;
*)
  GREP=grep
  ;;
esac
ZOO_DATADIR="$($GREP "^[[:space:]]*dataDir" "$ZOOCFG" | sed -e 's/.*=//')"
ZOO_DATADIR="$(echo -e "${ZOO_DATADIR}" | sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//')"
ZOO_DATALOGDIR="$($GREP "^[[:space:]]*dataLogDir" "$ZOOCFG" | sed -e 's/.*=//')"

# iff autocreate is turned off and the datadirs don't exist fail
# immediately as we can't create the PID file, etc..., anyway.
if [ -n "$ZOO_DATADIR_AUTOCREATE_DISABLE" ]; then
    if [ ! -d "$ZOO_DATADIR/version-2" ]; then
        echo "ZooKeeper data directory is missing at $ZOO_DATADIR fix the path or run initialize"
        exit 1
    fi

    if [ -n "$ZOO_DATALOGDIR" ] && [ ! -d "$ZOO_DATALOGDIR/version-2" ]; then
        echo "ZooKeeper txnlog directory is missing at $ZOO_DATALOGDIR fix the path or run initialize"
        exit 1
    fi
    ZOO_DATADIR_AUTOCREATE="-Dzookeeper.datadir.autocreate=false"
fi
# 在類linux系統上，當zookeeper啟動時，會建立一個用於儲存程序id的zookeeper_server.pid檔案（在資料目錄下），每次執行start、stop、restart命令時都會檢查這個命令來判斷zookeeper的啟動狀態，而前臺啟動命令start-foreground不會檢查這個檔案，所以 start-foreground 和其他命令不是一個系列，最好不混用。
# windows的zkServer.cmd 沒有這個 程序檔案 的操作
if [ -z "$ZOOPIDFILE" ]; then
    if [ ! -d "$ZOO_DATADIR" ]; then
        mkdir -p "$ZOO_DATADIR"
    fi
    ZOOPIDFILE="$ZOO_DATADIR/zookeeper_server.pid"
else
    # ensure it exists, otw stop will fail
    mkdir -p "$(dirname "$ZOOPIDFILE")"
fi

if [ ! -w "$ZOO_LOG_DIR" ] ; then
mkdir -p "$ZOO_LOG_DIR"
fi

ZOO_LOG_FILE=zookeeper-$USER-server-$HOSTNAME.log
_ZOO_DAEMON_OUT="$ZOO_LOG_DIR/zookeeper-$USER-server-$HOSTNAME.out"

case $1 in
start)
    echo  -n "Starting zookeeper ... "
    if [ -f "$ZOOPIDFILE" ]; then
      if kill -0 `cat "$ZOOPIDFILE"` > /dev/null 2>&1; then
# 如果zookeeper_server.pid中儲存的程序id代表的程序存在（kill -0 pid），說明zookeeper已經啟動了，無需再次啟動，指令碼退出執行
         echo $command already running as process `cat "$ZOOPIDFILE"`.
         exit 1
      fi
    fi
    nohup "$JAVA" $ZOO_DATADIR_AUTOCREATE "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" \
    "-Dzookeeper.log.file=${ZOO_LOG_FILE}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" \
    -XX:+HeapDumpOnOutOfMemoryError -XX:OnOutOfMemoryError='kill -9 %p' \
    -cp "$CLASSPATH" $JVMFLAGS $ZOOMAIN "$ZOOCFG" > "$_ZOO_DAEMON_OUT" 2>&1 < /dev/null &
    if [ $? -eq 0 ]
# 如果上面的啟動命令返回 0，說明執行成功，zookeeper啟動了，就要把 程序id 寫到zookeeper_server.pid檔案中
    then
      case "$OSTYPE" in
      *solaris*)
        /bin/echo "${!}\\c" > "$ZOOPIDFILE"
        ;;
      *)
        /bin/echo -n $! > "$ZOOPIDFILE"
        ;;
      esac
      if [ $? -eq 0 ];
      then
        sleep 1
        pid=$(cat "${ZOOPIDFILE}")
        if ps -p "${pid}" > /dev/null 2>&1; then
          echo STARTED
        else
          echo FAILED TO START
          exit 1
        fi
      else
        echo FAILED TO WRITE PID
        exit 1
      fi
    else
      echo SERVER DID NOT START
      exit 1
    fi
    ;;
# 前臺啟動命令
start-foreground)
    ZOO_CMD=(exec "$JAVA")
    if [ "${ZOO_NOEXEC}" != "" ]; then
      ZOO_CMD=("$JAVA")
    fi
    "${ZOO_CMD[@]}" $ZOO_DATADIR_AUTOCREATE "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" \
    "-Dzookeeper.log.file=${ZOO_LOG_FILE}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" \
    -XX:+HeapDumpOnOutOfMemoryError -XX:OnOutOfMemoryError='kill -9 %p' \
    -cp "$CLASSPATH" $JVMFLAGS $ZOOMAIN "$ZOOCFG"
    ;;
# 列印啟動命令
print-cmd)
    echo "\"$JAVA\" $ZOO_DATADIR_AUTOCREATE -Dzookeeper.log.dir=\"${ZOO_LOG_DIR}\" \
    -Dzookeeper.log.file=\"${ZOO_LOG_FILE}\" -Dzookeeper.root.logger=\"${ZOO_LOG4J_PROP}\" \
    -XX:+HeapDumpOnOutOfMemoryError -XX:OnOutOfMemoryError='kill -9 %p' \
    -cp \"$CLASSPATH\" $JVMFLAGS $ZOOMAIN \"$ZOOCFG\" > \"$_ZOO_DAEMON_OUT\" 2>&1 < /dev/null"
    ;;
# 停止服務：會判斷zookeeper_server.pid檔案是否存在，如果不存在說明zookeeper沒有執行
stop)
    echo -n "Stopping zookeeper ... "
    if [ ! -f "$ZOOPIDFILE" ]
    then
      echo "no zookeeper to stop (could not find file $ZOOPIDFILE)"
    else
# 停止服務就是執行兩條命令：
# 第一條kill pid，注意沒帶訊號變數，他會讓程序清理善後工作，而不是直接殺死程序；
# 第二條rm zookeeper_server.pid，刪除程序檔案，也就是說zookeeper 訪問沒有啟動的時候，是沒有這個檔案的
      $KILL $(cat "$ZOOPIDFILE")
      rm "$ZOOPIDFILE"
      echo STOPPED
    fi
    exit 0
    ;;
# 重啟服務：執行stop，等三秒，執行start
restart)
    shift
    "$0" stop ${@}
    sleep 3
    "$0" start ${@}
    ;;
# 查詢狀態
status)
    # -q is necessary on some versions of linux where nc returns too quickly, and no stat result is output
    clientPortAddress=`$GREP "^[[:space:]]*clientPortAddress[^[:alpha:]]" "$ZOOCFG" | sed -e 's/.*=//'`
    if ! [ $clientPortAddress ]
    then
   clientPortAddress="localhost"
    fi
    clientPort=`$GREP "^[[:space:]]*clientPort[^[:alpha:]]" "$ZOOCFG" | sed -e 's/.*=//'`
    if ! [[ "$clientPort"  =~ ^[0-9]+$ ]]
    then
       dataDir=`$GREP "^[[:space:]]*dataDir" "$ZOOCFG" | sed -e 's/.*=//'`
       myid=`cat "$dataDir/myid"`
       if ! [[ "$myid" =~ ^[0-9]+$ ]] ; then
         echo "clientPort not found and myid could not be determined. Terminating."
         exit 1
       fi
       clientPortAndAddress=`$GREP "^[[:space:]]*server.$myid=.*;.*" "$ZOOCFG" | sed -e 's/.*=//' | sed -e 's/.*;//'`
       if [ ! "$clientPortAndAddress" ] ; then
           echo "Client port not found in static config file. Looking in dynamic config file."
           dynamicConfigFile=`$GREP "^[[:space:]]*dynamicConfigFile" "$ZOOCFG" | sed -e 's/.*=//'`
           clientPortAndAddress=`$GREP "^[[:space:]]*server.$myid=.*;.*" "$dynamicConfigFile" | sed -e 's/.*=//' | sed -e 's/.*;//'`
       fi
       if [ ! "$clientPortAndAddress" ] ; then
          echo "Client port not found. Terminating."
          exit 1
       fi
       if [[ "$clientPortAndAddress" =~ ^.*:[0-9]+ ]] ; then
          clientPortAddress=`echo "$clientPortAndAddress" | sed -e 's/:.*//'`
       fi
       clientPort=`echo "$clientPortAndAddress" | sed -e 's/.*://'`
       if [ ! "$clientPort" ] ; then
          echo "Client port not found. Terminating."
          exit 1
       fi
    fi
    echo "Client port found: $clientPort. Client address: $clientPortAddress."
# 這裡會向 FourLetterWordMain 傳送 srvr命令，從返回結果中 找到包含Mode的行，最終顯示 該節點是leader還是follower
    STAT=`"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
             -cp "$CLASSPATH" $JVMFLAGS org.apache.zookeeper.client.FourLetterWordMain \
             $clientPortAddress $clientPort srvr 2> /dev/null    \
          | $GREP Mode`
    if [ "x$STAT" = "x" ]
    then
        echo "Error contacting service. It is probably not running."
        exit 1
    else
        echo $STAT
        exit 0
    fi
    ;;
# 對於不認識的命令，列印幫助資訊
*)
    echo "Usage: $0 [--config <conf-dir>] {start|start-foreground|stop|restart|status|print-cmd}" >&2

esac