Fix signal handler

[elfring]

The function "exit" does not belong to the list of async-signal-safe functions. I guess that a different program design will be needed for your function "terminate".

[simsong]

Thanks for documenting all of these problems. Would you like to submit pull requests with the fixes?

[elfring]

Would you like to consider other software design options?

• sigwaitinfo()
• Self-pipe trick
• Signal-safe locks