确认toolrunner不是线程安全的：

原始代码（遇到问题）：

public static int run(Configuration conf, Tool tool, String[] args) 
throws Exception{
if(conf == null) {
  conf = new Configuration();
}
GenericOptionsParser parser = new GenericOptionsParser(conf, args);
//set the configuration back, so that Tool can configure itself
tool.setConf(conf);

//get the args w/o generic hadoop args
String[] toolArgs = parser.getRemainingArgs();
return tool.run(toolArgs);

}

新代码（有效）：

public static int run(Configuration conf, Tool tool, String[] args)
        throws Exception{
    if(conf == null) {
        conf = new Configuration();
    }
    GenericOptionsParser parser = getParser(conf, args);

    tool.setConf(conf);

    //get the args w/o generic hadoop args
    String[] toolArgs = parser.getRemainingArgs();
    return tool.run(toolArgs);
}

private static synchronized GenericOptionsParser getParser(Configuration conf, String[] args) throws Exception {
    return new GenericOptionsParser(conf, args);
}