Cancel blocking `poll`?

So, I've run into this issue where I have many threads calling poll on different file descriptors. When I want to add a new one, I need to cancel one of those polls, add a new one, and continue. That alone sounds bad, but also I can't even see how to do that.

Some relevant code:

struct pollfd fds[size];
for(int i = 0;i<size;i++) {
    struct pollfd fd;
    fd.fd = body[i];
    fd.events = POLLIN;
    fd.revents = 0;
    fds[i] = fd;
}
if(poll(&fds[0], (nfds_t)size, -1) < 0) return NULL;

(I'm using this through JNI also).

I figure I could set a really low delay on poll, and call it over and over, but I think that would begin to defeat the purpose.

via Chebli Mohamed