Libevent provides cross-platform asynchronous callbacks on sockets and file descriptors. Different operating systems have different ways of handling this efficiently, for example linux has kernel support for this operation which can scale to tens of thousands of sockets. It’s all pretty complicated but libevent makes it very simple. Along with a basic api that is used by highly scalable projects like memcached and thrift, it also has asyncronus a dns lookup api and a http server api.

Here’s an example of how simple it is to write a basic http server.

#include <sys/types.h>
#include <sys/time.h>
#include <sys/queue.h>#include <stdlib.h>

#include <err.h>
#include <event.h>
#include <evhttp.h>

void generic_handler(struct evhttp_request *req, void *arg)
{
        struct evbuffer *buf;
        buf = evbuffer_new();

        if (buf == NULL)
            err(1, "failed to create response buffer");

        evbuffer_add_printf(buf, "Requested: %sn", evhttp_request_uri(req));
        evhttp_send_reply(req, HTTP_OK, "OK", buf);
}

int main(int argc, char **argv)
{
    struct evhttp *httpd;

    event_init();
    httpd = evhttp_start("0.0.0.0", 8080);

    /* Set a callback for requests to "/specific". */
    /* evhttp_set_cb(httpd, "/specific", another_handler, NULL); */

    /* Set a callback for all other requests. */
    evhttp_set_gencb(httpd, generic_handler, NULL);

    event_dispatch();

    /* Not reached in this code as it is now. */
    evhttp_free(httpd);

    return 0;
}

But is it fast? check out the benchmarks (on my laptop):

ab -c 1000 -n 10000 http://localhost/

Apache2: Requests per second: 1274.14 [#/sec] (mean)

libevent: Requests per second: 1584.37 [#/sec] (mean)

Kickass!

This entry was posted on Tuesday, March 25th, 2008 at 9:47 pm and is filed under libevent, web service. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.