如何监控一个ZeroMQ服务器是否存在？

Question

我想在发送 ZeroMQ 请求之前检查服务器是否存在（状态），但我不知道该怎么做。

Answer 1

Q : I want to check the existence ( state ) of a server before I send a ZeroMQ request

解决方案是设置和使用 zmq_socket_monitor()

的服务

// 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
                    )
{   
    zmq_msg_t msg;
    zmq_msg_init ( &msg );                                       // First frame in message contains event number and value
    if ( zmq_msg_recv ( &msg, monitor, 0 ) == -1 ) return -1;    // Interrupted, presumably
    assert ( zmq_msg_more ( &msg )              & "REASON: Frame #1 FAILED TO SIG 2nd, EXPECTED, FRAME TO COME" );

    uint8_t  *data  =  ( uint8_t  * ) zmq_msg_data ( &msg );
    uint16_t  event = *( uint16_t * ) ( data );

    if ( value )
        *value = *( uint32_t * ) ( data + 2 );


    zmq_msg_init ( &msg );                                      // Second frame in message contains event address
    if ( zmq_msg_recv ( &msg, monitor, 0 ) == -1 ) return -1;   // Interrupted, presumably
    assert ( !zmq_msg_more ( &msg )             & "REASON: Frame #2 FAILED TO SIG more, NOT EXPECTED, FRAMEs TO COME" );

    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                                & "REASON: Context FAILED to instantiate" );

    void    *client = zmq_socket ( ctx, ZMQ_DEALER );
    assert ( client                             & "REASON: Socket FAILED to instantiate" );

 // Socket monitoring only works over inproc://
    int      rc = zmq_socket_monitor ( client, "inproc://monitor-client-side", ZMQ_EVENT_ALL );
    assert ( rc == 0                            & "REASON: socket_monitor FAILED to instantiate over INPROC:// transport-class" );

 // Create socket for collecting monitor events
    void    *client_side_mon = zmq_socket ( ctx, ZMQ_PAIR );
    assert ( client_side_mon                    & "REASON: socket_monitor receiving Socket FAILED to instantiate " );

 // Connect these to the inproc endpoints so they'll get events
             rc = zmq_connect ( client_side_mon, "inproc://monitor-client-side" );
    assert ( rc == 0                            & "REASON: .connect()-method FAILED to get connected" );

 // Now do whatever you need
    ...

 // Close client
    close_zero_linger ( client );

 // --------------------------------------------------------------------
 // How to collect and check events from socket_monitor:
    int  event =  get_monitor_event ( client_side_mon, NULL, NULL );

    if ( event == ZMQ_EVENT_CONNECT_DELAYED )
         event =  get_monitor_event ( client_side_mon, NULL, NULL );

    assert ( event == ZMQ_EVENT_CONNECTED       & "REASON: [client]-socket still not in an expected, .connect()-ed, state" );
    ...

    ...
    event = get_monitor_event ( client_side_mon, NULL, NULL );
    assert ( event == ZMQ_EVENT_MONITOR_STOPPED & "REASON: [client]-socket not in an expected, .close()-ed, state" );

 // --------------------------------------------------------------------
 // FINALLY:
 // --------------------------------------------------------------------
 // Close down the sockets
    close_zero_linger ( client_side_mon );

    zmq_ctx_term ( ctx );

    return 0;
    }

_{（自 v3.2+ 起包含在 API 中）}

Answer 2

在认为套接字正常工作之前，您最好在客户端和服务器之间建立一个完整的连接并设计一个简单的 ACK 协议。如果客户端在合理时间内收到 ACK，则服务器启动。否则服务器宕机，客户端最好关闭套接字再试，直到成功。

N.B。如果套接字未关闭，则消息可能会在 ZMQ 发送队列中堆积，并有可能在服务器最终连接时用大量 ACK 消息淹没服务器。

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