be-arg-val.c

#include <stdio.h>
#include <stdlib.h>
#include <event2/event.h>
#include <event2/bufferevent.h>

struct arg
{
    int i;
    int *i_ptr;
};
int events, events_max = 2;
struct bufferevent *pair[2];

static void arg_inc(struct arg *arg, const char *pref)
{
    arg->i_ptr = malloc(sizeof(arg->i));
    *arg->i_ptr = arg->i;
    ++*arg->i_ptr;
    printf("%s(i)=%i\n", pref, *arg->i_ptr);
}

static void read_cb(struct bufferevent *be, void *_arg)
{
    struct arg *arg = _arg;
    arg_inc(arg, "read_cb");

    /** pass i_ptr next, but do not forget to free it */
}
static void write_cb(struct bufferevent *be, void *_arg)
{
    struct arg *arg = _arg;
    arg_inc(arg, "write_cb");

    if (++events < events_max) {
        bufferevent_write(pair[1], "foo", 3);
    }

    /** pass i_ptr next, but do not forget to free it */
}

int main()
{
    struct arg arg = { 0 };

    struct event_base *base = event_base_new();
    bufferevent_pair_new(base, 0, pair);

    bufferevent_enable(pair[0], EV_READ);

    bufferevent_setcb(pair[0], read_cb, NULL, NULL, &arg);
    bufferevent_setcb(pair[1], NULL, write_cb, NULL, &arg);

    bufferevent_write(pair[1], "foo", 3);

    event_base_dispatch(base);

    /** XXX: leaks */

    return 0;
}

be-arg.c

#include <stdio.h>
#include <event2/event.h>
#include <event2/bufferevent.h>

struct arg
{
    int i;
};
int events, events_max = 2;
struct bufferevent *pair[2];

static void read_cb(struct bufferevent *be, void *_arg)
{
    struct arg *arg = _arg;
    ++arg->i;
    printf("read_cb(i)=%i\n", arg->i);
}
static void write_cb(struct bufferevent *be, void *_arg)
{
    struct arg *arg = _arg;
    ++arg->i;
    printf("write_cb(i)=%i\n", arg->i);

    if (++events < events_max) {
        bufferevent_write(pair[1], "foo", 3);
    }
}

int main()
{
    struct arg arg = { 0 };

    struct event_base *base = event_base_new();
    bufferevent_pair_new(base, 0, pair);

    bufferevent_enable(pair[0], EV_READ);

    bufferevent_setcb(pair[0], read_cb, NULL, NULL, &arg);
    bufferevent_setcb(pair[1], NULL, write_cb, NULL, &arg);

    bufferevent_write(pair[1], "foo", 3);

    event_base_dispatch(base);

    /** XXX: leaks */

    return 0;
}