ZeroMQ

Binary Star Reactor

Binary Star is useful and generic enough to package up as a reusable reactor class. The reactor then runs and calls our code whenever it has a message to process. This is much nicer than copying/pasting the Binary Star code into each server where we want that capability.

In C, we wrap the CZMQ zloop class that we saw before. zloop lets you register handlers to react on socket and timer events. In the Binary Star reactor, we provide handlers for voters and for state changes (active to passive, and vice versa). Here is the bstar API:

//  Create a new Binary Star instance, using local (bind) and
//  remote (connect) endpoints to set up the server peering
bstar_t *bstar_new (int primary, char *local, char *remote);

//  Destroy a Binary Star instance
void bstar_destroy (bstar_t **self_p);

//  Return underlying zloop reactor, for timer and reader
//  registration and cancelation
zloop_t *bstar_zloop (bstar_t *self);

//  Register voting reader
int bstar_voter (bstar_t *self, char *endpoint, int type,
                 zloop_fn handler, void *arg);

//  Register main state change handlers
void bstar_new_active (bstar_t *self, zloop_fn handler, void *arg);
void bstar_new_passive (bstar_t *self, zloop_fn handler, void *arg);

//  Start the reactor, which ends if a callback function returns -1, 
//  or the process received SIGINT or SIGTERM
int bstar_start (bstar_t *self);

The class implementation is in Example 4-68.

Example 4-68. Binary Star core class (bstar.c)

/* ===================================================================== ...