hdfs delete a file being written - hadoop

Question

Acording the blog, hdfs uses the lease mechanism to avoid two client writing the same file. So I think one can not delete the file which is written by the other client. Howerver, it's wrong.
When client A is writing the lock.txt, client B can delete lock.txt immediately. Client A can continue writing although the file no longer exists. Just when closing the stream, A will encounter the exception:
org.apache.hadoop.hdfs.server.namenode.LeaseExpiredException: No lease on /user/lock.txt (inode 643845185): File does not exist. Holder DFSClient_NONMAPREDUCE_-1636584585_1 does not have any open files**
Why this happen? My haddop version is 2.7.3.
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This is my test code：
// write process
object Create {
private val filePath = "/user/lock.txt"
def main(args: Array[String]): Unit = {
println("Create start!")
val fs = FileSystem.get(new Configuration())
val os = Option(fs.create(new Path(filePath), false))
if (os.isDefined) {
println(s"Create result! $os", System.currentTimeMillis())
0.until(300).foreach(index => {
os.get.write(100)
os.get.flush()
println("Writing...")
Thread.sleep(1000)
})
println("pre close" + System.currentTimeMillis())
os.get.close()
println("close success!" + System.currentTimeMillis())
}
}
}
// delete process
object Delete {
private val filePath = "/user/lock.txt"
def main(args: Array[String]): Unit = {
println("Delete start!")
val fs = FileSystem.get(new Configuration())
while (!fs.exists(new Path(filePath))) {
println("File no exist!")
Thread.sleep(1000)
}
println("File exist!")
while (true) {
println("try delete!")
val tmp = Option(fs.delete(new Path(filePath), false))
if (tmp.isDefined) {
println(s"delete result:${tmp.get}!" + System.currentTimeMillis())
}
println("Try recover")
if (fs.asInstanceOf[DistributedFileSystem].recoverLease(new Path(filePath))) {
println("Recover lease success!")
val res = Option(fs.delete(new Path(filePath), false))
println(s"File delete success:${res.get}")
} else {
println("Recover lease failed!")
}
Thread.sleep(1000)
}
}
}