程式退出時無法正常return 0，而是跑出了如下錯誤
terminate called without an active exception
Aborted (core dumped)
丟進gdb發現在std::thread的dtor裡面呼叫了terminate，往上爬callstack到關鍵的frame
(gdb) info frame
Stack level 5, frame at 0x7ffc2b28cf30:
rip = 0x555c598ccf29 in std::thread::~thread (/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/g++-v9/thread:139); saved rip = 0x555c598dbbc0
called by frame at 0x7ffc2b28cf50, caller of frame at 0x7ffc2b28cf10
source language c++.
Arglist at 0x7ffc2b28cf20, args: this=0x7ffc2b28cff0, __in_chrg=<optimized out>
Locals at 0x7ffc2b28cf20, Previous frame's sp is 0x7ffc2b28cf30
Saved registers:
rbp at 0x7ffc2b28cf20, rip at 0x7ffc2b28cf28
直接把thread id找出來
(gdb) print *this
$8 = {_M_id = {_M_thread = 140139420739328}}
轉成hex format是7F74C0646700，對照thread list發現是thread4還沒離開，所以在thread1殺不掉這個物件
(gdb) info thread
Id Target Id Frame
* 1 Thread 0x7f74c064a800 (LWP 9151) "main" 0x0000555c598ccf29 in std::thread::~thread (this=0x7ffc2b28cff0, __in_chrg=<optimized out>) at /usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/g++-v9/thread:139
4 Thread 0x7f74c0646700 (LWP 9157) "main" 0x00007f74c1405eb2 in epoll_wait () from /lib64/libc.so.6
5 Thread 0x7f74bfd11700 (LWP 9158) "main" 0x00007f74c14de6d7 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
27 Thread 0x7f748d7fa700 (LWP 9180) "grpc_shutdown" 0x00007f74c1388977 in unlink_chunk.isra () from /lib64/libc.so.6
去看看thread4在執行什麼(跳過)，找到當初建立thread的object，呼叫detach()，收工
