#include <nng/nng.h>
#include <nng/supplemental/util/platform.h>
typedef struct nng_cv nng_cv;
int nng_cv_alloc(nng_cv **cvp, nng_mtx *mtx);The nng_cv_alloc() function allocates a condition variable, using
the mutex mtx, and returns it in cvp.
Every condition variable is associated with a mutex, which must be
owned when a thread waits for the condition using
nng_cv_wait() or
nng_cv_until().
The mutex must also be owned when signaling the condition using the
nng_cv_wake() or
nng_cv_wake1() functions.