如何将syscall.Errno传递给os.Exit？

Question

Let's say I try to acquire a lock, fail, and want to exit the program.

err = syscall.Flock(lockfd, syscall.LOCK_EX|syscall.LOCK_NB)
if err == syscall.EAGAIN {
    os.Exit(err)
}

The problem is you need to pass an integer to os.Exit.

I've tried:

os.Exit(int(err))
os.Exit(syscall.EAGAIN)

// Compiles fine, but the cast fails.. no idea why
eerr, _ := err.(*syscall.Errno); os.Exit(int(*eerr)) 

// panics
reflect.ValueOf(err).Int()

It seems like you can compare the syscall.Errno to other integers, but actually trying to get the value of it is escaping me...

Answer 1

You can normally just convert a syscall.Errno to an int

if err == syscall.EAGAIN {
    os.Exit(int(err))
}

syscall.Errno is defined as a uintptr, which can be converted directly to an int. There's no interface, assertion, or reflection involved.

But when receiving it as an error interface, you need to assert it first.

if err == syscall.EAGAIN {
    os.Exit(int(err.(syscall.Errno)))
}

The syscall.Errno is used as a value, not a pointer, no need to try and dereference it with *.