stated (prounounced "state dee") is a publish/subscribe mechanism that allows programs to publish their current state, and notify other interested programs when the state changes.
Initial development efforts are focused on FreeBSD, but the program should be easily portable to other Unix-like operating systems.
Run the following to build and install stated:
make
sudo make install
To enable stated to start at boot, run the following commands as root(for FreeBSD):
echo 'stated_enable="YES"' >> /etc/rc.conf
service stated start
stated should be considered beta-quality software, and there are known bugs.
The biggest problem is that the codepaths for publishing "system" state are incomplete. This means that publishing state for processes running under uid 0 isn't working yet.
Here is a simple example that shows two programs; one acting as the publisher, and the other as the subscriber.
The code for the publisher:
state_init();
state_bind("com.example.hello_world", 0644);
state_publish("com.example.hello_world", "hi", 2);The code for the subscriber:
state_init();
state_subscribe("com.example.hello_world");
for (;;) {
notify_state_t ns;
int statefd;
fd_set fds;
statefd = state_get_fd();
do {
int result;
FD_ZERO(&fds);
FD_SET(statefd, &fds);
result = select(statefd + 1, &fds, NULL, NULL, NULL);
} while (result == -1 && errno == EINTR);
if (state_check(&ns, 1) == 1) {
printf("the new state is: %s\n", ns->ns_state);
}
}