Manage all processes with GuardedProcessPool

[Mygod]

Type of changes

• General refinement

Details

This way we can destroy the processes and wait for them to exit in parallel, and ensure the process is destroyed so that we won't encounter strange port being used issue at the same time.

This addresses #1740 but probably doesn't fix it.

[madeye]

I think we need sigkill after waitfor timeout. Otherwise, it may not fix #1740.

[Mygod]

Process.waitFor requires API 26. And I'd also rather not use sigkill unless necessary. Could you investigate what would cause ss-local to ignore sigterm?

[madeye]

Actually, I cannot report the issue locally.

According to the report:

1。断开正常连接，切换到错误配置，连接报错，关闭连接。切换到正常配置，连接报错。
2，断开正常连接，切换到错误配置，连接报错，不关闭直接切换到正常配置，连接正常。

[Mygod]

Yes. Me neither. But there does seem to be some edge cases where libss-local doesn't respond to SIGTERM. For example, in #1742 when the socket is accidentally not protected, or the new example I just posted at #1740.

[madeye]

After instrumenting ss-local, my observation is that the ss-local process hangs when stop_plugin(). It means it handles SIGTERM correctly, but the child process didn't.

ss-local calls cork_subprocess_group_abort then waitpid until the child process finished.

https://github.com/shadowsocks/libcork/blob/c9b3ea9638b3adcbc07ee229fd630f439cdecae8/src/libcork/posix/subprocess.c#L483

[Mygod]

@madeye Okay. Here's the source code: shadowsocks/kcptun-android#32