linux上进程打开句柄最大值是1024， 这只是默认情况而已：
ubuntu@VM-0-15-ubuntu:~$ ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 3306 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 8192 cpu time (seconds, -t) unlimited max user processes (-u) 3306 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited ubuntu@VM-0-15-ubuntu:~$ ubu
