This is an issue with poll (and epoll) on Linux. If a file descriptor for a connected socket is polled with a request event mask of 0, and if the connection is abruptly terminated (RST) then the poll wakes up with the POLLHUP (and maybe POLLERR) bit set in the returned event set. The implication ...

源码参见:hadoop-common-{version}.jar , Shell.java line 370 : winUtilsPath = getQualifiedBinPath("winutils.exe"); 调用链中：函数checkHadoopHome() 找不到hadoop安装目录引起的报NPE

递归查询大家都知道，常见的如一张表，包含id(主键),parent_id（该记录的父亲id）,比如我们要从某1个id往下找他所有的儿子还有孙子（这时候心里要有一颗树的形象），该怎么写？