Use signalfd to handle SIGINT and SIGTERM shutdown.

adsbus/asyncaddrinfo.c

@@ -2,6 +2,7 @@
 #include <fcntl.h>
 #include <netdb.h>
 #include <pthread.h>
+#include <signal.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
@@ -28,6 +29,11 @@ static int asyncaddrinfo_write_fd;
 
 static void *asyncaddrinfo_main(void *arg) {
 	int fd = (int) (intptr_t) arg;
+
+	sigset_t sigmask;
+	assert(!sigfillset(&sigmask));
+	assert(!pthread_sigmask(SIG_BLOCK, &sigmask, NULL));
+
 	struct asyncaddrinfo_resolution *res;
 	ssize_t len;
 	while ((len = recv(fd, &res, sizeof(res), 0)) == sizeof(res)) {