kill会被信号打断吗？

Question

For example, if I use kill (a function in C library signal.h) to emit a SIGINT signal to a child, will the SIGCHLD signal from the child be caught before the kill function returns?

Answer 1

While the kill syscall isn't interruptible (at least according to the man page ), there's still at least two cases in which the SIGCHLD handler could run before the function returns:

1. If there's another thread in your process, the kernel could choose to run the signal handler there even before the kill syscall returns in your first thread.
2. You're probably using a wrapper function for kill from your libc. The signal handler could run in between the syscall returning to it, and it returning to your code.

So if you want to make sure you don't get the SIGCHLD until after kill returns, then you need to use sigprocmask to block it before the kill until you're ready for it.

Answer 2

I don't know if this answers your question but, reading the Linux man page, the possible return values of kill are EINVAL , EPERM , and ESRCH . EINTR is not one of them. That makes me think that the function won't be interrupted. At least, the system call won't be interrupted.

EDIT: I mean errno , not return, values.

Answer 3

Signal handling is asynchronous. There is therefore no guarantee either way about whether the SIGCHLD emitted when the child terminates will be received by the parent before the kill call returns. My guess would be that kill will usually win the race and return before the SIGCHLD arrives, but it is not safe to depend on that.