Provided by: libzmq3-dev_4.1.4-7ubuntu0.1_amd64 
NAME
zmq_socket_monitor - monitor socket events
SYNOPSIS
int zmq_socket_monitor (void *socket, char *endpoint, int events);
DESCRIPTION
The zmq_socket_monitor() method lets an application thread track socket events (like
connects) on a ZeroMQ socket. Each call to this method creates a ZMQ_PAIR socket and binds
that to the specified inproc:// endpoint. To collect the socket events, you must create
your own ZMQ_PAIR socket, and connect that to the endpoint.
The events argument is a bitmask of the socket events you wish to monitor, see Supported
events below. To monitor all events, use the event value ZMQ_EVENT_ALL.
Each event is sent as two frames. The first frame contains an event number (16 bits), and
an event value (32 bits) that provides additional data according to the event number. The
second frame contains a string that specifies the affected TCP or IPC endpoint.
The _zmq_socket_monitor()_ method supports only connection-oriented
transports, that is, TCP, IPC, and TIPC.
SUPPORTED EVENTS
ZMQ_EVENT_CONNECTED
The socket has successfully connected to a remote peer. The event value is the file
descriptor (FD) of the underlying network socket. Warning: there is no guarantee that the
FD is still valid by the time your code receives this event.
ZMQ_EVENT_CONNECT_DELAYED
A connect request on the socket is pending. The event value is unspecified.
ZMQ_EVENT_CONNECT_RETRIED
A connect request failed, and is now being retried. The event value is the reconnect
interval in milliseconds. Note that the reconnect interval is recalculated at each retry.
ZMQ_EVENT_LISTENING
The socket was successfully bound to a network interface. The event value is the FD of the
underlying network socket. Warning: there is no guarantee that the FD is still valid by
the time your code receives this event.
ZMQ_EVENT_BIND_FAILED
The socket could not bind to a given interface. The event value is the errno generated by
the system bind call.
ZMQ_EVENT_ACCEPTED
The socket has accepted a connection from a remote peer. The event value is the FD of the
underlying network socket. Warning: there is no guarantee that the FD is still valid by
the time your code receives this event.
ZMQ_EVENT_ACCEPT_FAILED
The socket has rejected a connection from a remote peer. The event value is the errno
generated by the accept call.
ZMQ_EVENT_CLOSED
The socket was closed. The event value is the FD of the (now closed) network socket.
ZMQ_EVENT_CLOSE_FAILED
The socket close failed. The event value is the errno returned by the system call. Note
that this event occurs only on IPC transports.
ZMQ_EVENT_DISCONNECTED
The socket was disconnected unexpectedly. The event value is the FD of the underlying
network socket. Warning: this socket will be closed.
ZMQ_EVENT_MONITOR_STOPPED
Monitoring on this socket ended.
RETURN VALUE
The zmq_socket_monitor() function returns a value of 0 or greater if successful. Otherwise
it returns -1 and sets errno to one of the values defined below.
ERRORS
ETERM
The 0MQ context associated with the specified socket was terminated.
EPROTONOSUPPORT
The requested transport protocol is not supported. Monitor sockets are required to use
the inproc:// transport.
EINVAL
The endpoint supplied is invalid.
EXAMPLE
Monitoring client and server sockets.
// Read one event off the monitor socket; return value and address
// by reference, if not null, and event number by value. Returns -1
// in case of error.
static int
get_monitor_event (void *monitor, int *value, char **address)
{
// First frame in message contains event number and value
zmq_msg_t msg;
zmq_msg_init (&msg);
if (zmq_msg_recv (&msg, monitor, 0) == -1)
return -1; // Interruped, presumably
assert (zmq_msg_more (&msg));
uint8_t *data = (uint8_t *) zmq_msg_data (&msg);
uint16_t event = *(uint16_t *) (data);
if (value)
*value = *(uint32_t *) (data + 2);
// Second frame in message contains event address
zmq_msg_init (&msg);
if (zmq_msg_recv (&msg, monitor, 0) == -1)
return -1; // Interruped, presumably
assert (!zmq_msg_more (&msg));
if (address) {
uint8_t *data = (uint8_t *) zmq_msg_data (&msg);
size_t size = zmq_msg_size (&msg);
*address = (char *) malloc (size + 1);
memcpy (*address, data, size);
*address [size] = 0;
}
return event;
}
int main (void)
{
void *ctx = zmq_ctx_new ();
assert (ctx);
// We'll monitor these two sockets
void *client = zmq_socket (ctx, ZMQ_DEALER);
assert (client);
void *server = zmq_socket (ctx, ZMQ_DEALER);
assert (server);
// Socket monitoring only works over inproc://
int rc = zmq_socket_monitor (client, "tcp://127.0.0.1:9999", 0);
assert (rc == -1);
assert (zmq_errno () == EPROTONOSUPPORT);
// Monitor all events on client and server sockets
rc = zmq_socket_monitor (client, "inproc://monitor-client", ZMQ_EVENT_ALL);
assert (rc == 0);
rc = zmq_socket_monitor (server, "inproc://monitor-server", ZMQ_EVENT_ALL);
assert (rc == 0);
// Create two sockets for collecting monitor events
void *client_mon = zmq_socket (ctx, ZMQ_PAIR);
assert (client_mon);
void *server_mon = zmq_socket (ctx, ZMQ_PAIR);
assert (server_mon);
// Connect these to the inproc endpoints so they'll get events
rc = zmq_connect (client_mon, "inproc://monitor-client");
assert (rc == 0);
rc = zmq_connect (server_mon, "inproc://monitor-server");
assert (rc == 0);
// Now do a basic ping test
rc = zmq_bind (server, "tcp://127.0.0.1:9998");
assert (rc == 0);
rc = zmq_connect (client, "tcp://127.0.0.1:9998");
assert (rc == 0);
bounce (client, server);
// Close client and server
close_zero_linger (client);
close_zero_linger (server);
// Now collect and check events from both sockets
int event = get_monitor_event (client_mon, NULL, NULL);
if (event == ZMQ_EVENT_CONNECT_DELAYED)
event = get_monitor_event (client_mon, NULL, NULL);
assert (event == ZMQ_EVENT_CONNECTED);
event = get_monitor_event (client_mon, NULL, NULL);
assert (event == ZMQ_EVENT_MONITOR_STOPPED);
// This is the flow of server events
event = get_monitor_event (server_mon, NULL, NULL);
assert (event == ZMQ_EVENT_LISTENING);
event = get_monitor_event (server_mon, NULL, NULL);
assert (event == ZMQ_EVENT_ACCEPTED);
event = get_monitor_event (server_mon, NULL, NULL);
assert (event == ZMQ_EVENT_CLOSED);
event = get_monitor_event (server_mon, NULL, NULL);
assert (event == ZMQ_EVENT_MONITOR_STOPPED);
// Close down the sockets
close_zero_linger (client_mon);
close_zero_linger (server_mon);
zmq_ctx_term (ctx);
return 0 ;
}
SEE ALSO
zmq(7)
AUTHORS
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