ZeroMQ

Binary Star Implementation

Without further ado, here is a proof-of-concept implementation of the Binary Star server, beginning with Example 4-61. The primary and backup servers run the same code, and their roles are chosen by the invoker.

Example 4-61. Binary Star server (bstarsrv.c)

//
//  Binary Star server proof-of-concept implementation. This server does no
//  real work; it just demonstrates the Binary Star failover model.

#include "czmq.h"

//  States in which we can be at any point in time
typedef enum {
    STATE_PRIMARY = 1,          //  Primary, waiting for peer to connect
    STATE_BACKUP = 2,           //  Backup, waiting for peer to connect
    STATE_ACTIVE = 3,           //  Active - accepting connections
    STATE_PASSIVE = 4           //  Passive - not accepting connections
} state_t;

//  Events, which start with the states our peer can be in
typedef enum {
    PEER_PRIMARY = 1,           //  HA peer is pending primary
    PEER_BACKUP = 2,            //  HA peer is pending backup
    PEER_ACTIVE = 3,            //  HA peer is active
    PEER_PASSIVE = 4,           //  HA peer is passive
    CLIENT_REQUEST = 5          //  Client makes request
} event_t;

//  Our finite-state machine
typedef struct {
    state_t state;              //  Current state
    event_t event;              //  Current event
    int64_t peer_expiry;        //  When peer is considered "dead"
} bstar_t;

//  We send state information this often
//  If peer doesn't respond in two heartbeats, it is "dead"
#define HEARTBEAT 1000          //  In msec

The heart of the Binary Star design is its finite-state machine (FSM). The FSM runs one event at a time. We apply an event to the current state, which ...