为什么在处理来自multiprocess.Process的异常时，只有当你自己抛出异常时，才能捕获KeyboardInterrupt异常？

import multiprocessing
import signal

class CustomException(Exception):
    pass

def child_process():
    # 重新定义信号处理器
    signal.signal(signal.SIGINT, signal.SIG_IGN)
    signal.signal(signal.SIGTERM, signal.SIG_IGN)
    
    try:
        # 子进程执行的代码
        # ...
        # 当需要中断子进程时，抛出自定义异常
        raise CustomException("Child process interrupted")
    except CustomException as e:
        # 在子进程中捕获自定义异常并打印
        print("Child process exception:", e)

if __name__ == '__main__':
    try:
        # 创建子进程
        p = multiprocessing.Process(target=child_process)
        p.start()
        p.join()
    except KeyboardInterrupt:
        # 在主进程中捕获KeyboardInterrupt异常并打印
        print("Main process KeyboardInterrupt")