当Xcode闪退提示“Message from debugger: Terminated due to signal 9”时，意思是程序收到信号9主动退出应用。收到信号9的原因有：内存不足，或CPU使用率过高时，程序主动终止了运行。
signal 是Linux/Unix 中的 signal 。来着：https://www.lifewire.com/signal-linux-command-4094016
Term: Default action is to terminate the process.//默认终止进程
Ign: Default action is to ignore the signal.//默认忽略信号
Core: Default action is to terminate the process and dump core.//默认终止进程并且内核转储
Stop: Default action is to stop the process.//默认停止进程
| Signal | Value | Action | Comment |
|---|---|---|---|
| or death of controlling process | |||
| SIGINT | 2 | Term | Interrupt from |
| SIGQUIT | 3 | Core | Quit from |
| SIGILL | 4 | Core | illegal |
| SIGABRT | 6 | Core | Abort signal |
| SIGFPE | 8 | Core | Floating point |
| SIGKILL | 9 | Term | Kill signal |
| SIGSEGV | 11 | Core | Invalid memory |
| SIGPIPE | 13 | Term | Broken pipe: write to pipe with no readers |
| SIGALRM | 14 | Term | Timer signal |
| SIGTERM | 15 | Term | Termination signal |
| SIGUSR | 130,10,16 | Term | User-defined signal 1 |
| SIGUSR2 | 31,12,17 | Term | User-defined signal 2 |
| SIGCHLD | 20,17,18 | Ign | Child stopped or terminated |
| SIGCONT | 19,18,25 | Continue if stopped | |
| SIGSTOP | 17,19,23 | Stop | Stop process |
| SIGTSTP | 18,20,24 | Stop | Stop typed at tty |
| SIGTTIN | 21,21,26 | Stop | tty input for background process |
| SIGTTOU | 22,22,27 | Stop | tty output for background process |