问题描述
从信号处理程序中调用msgsnd函数是否安全?
Is it safe to invoke msgsnd function from signal handler?
我们的服务代码并非旨在每一个正常完成，所以我没有退出点，但是当服务停止时，我需要向另一个进程发送消息，因此我需要捕获SIGTERM并执行msgsnd调用exit(0).
Code for our services is not intended to every gracefully complete, so I don't have exit point, however I need to send message to another process when services is stopped, so I need to catch SIGTERM and perform msgsnd before calling exit(0).
那样安全吗?
我查看了信号安全手册页并且在列表中未找到msgsnd.我应该认为这是不安全的功能吗?可能会有什么后果?
I looked into signal safety manual page and did not found msgsnd in the list. Should I consider this as unsafe function? What are the possible consequences?
推荐答案
不，这不安全. (请注意，exit()不会出现在 async-signal-安全功能列表，尽管_exit()确实如此.)
No, it's not safe. (Note that exit() doesn't appear on the async-signal-safe function list, either, though _exit() does.)
msgsnd可能会静默失败，可能会出错，可能出现段错误，可能永远挂起等.
msgsnd might silently fail, might error out, might segfault, might hang forever, etc.
考虑一下重构-如果您需要对SIGTERM做一些事情，那么我会说您 do 需要优美的，或者至少不是笨拙的关闭逻辑.如果那不可行，也许 SEM_UNDO 可以做你想要的，因为您似乎已经对SysV IPC感到满意.或持有在进程终止时释放的文件系统锁.或者让服务父捕获SIGCHLD，然后调用msgsnd.等等.
Consider refactoring a bit — if you need to do something upon SIGTERM then I'd say you do need graceful, or at least not clumsy, shutdown logic. If that's not feasible, perhaps SEM_UNDO can do what you want, as you seem to be comfortable with SysV IPC already. Or hold a file-system lock that is released upon process death. Or have the service parent catch SIGCHLD and then call msgsnd. Etc.
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