mod_loadshed.c

mod_loadshed.c

/**
 * \file mod_loadshed.c
 * \author Mark Nottingham, <mnot@mnot.net>
 *
 * mod_loadshed, when enabled, will refuse the request with a 503 if
 * no additional Apache children are currently available. This should
 * prevent requests from going to the listen queue.
 */


#include "httpd.h"
#include "http_core.h"
#include "http_config.h"
#include "http_log.h"
#include "scoreboard.h"
#include <stdio.h>


MODULE_VAR_EXPORT module  loadshed_module;

typedef struct  {
	int             enabled;
}  loadshed_cfg;


static void *mkconfig(pool *p)
{
    loadshed_cfg *cfg = ap_pcalloc(p, sizeof(loadshed_cfg));

    cfg->enabled = 0;
    return cfg;
}

/*
 * Respond to a callback to create configuration record for a server or
 * vhost environment.
 */
static void *create_mconfig_for_server(pool *p, server_rec *s)
{
    return mkconfig(p);
}

/*
 * Respond to a callback to create a config record for a specific directory.
 */
static void *create_mconfig_for_directory(pool *p, char *dir)
{
    return mkconfig(p);
}

/*
 * Handler for the LoadShed directive, which is FLAG.
 */
static const char *set_loadshed(cmd_parms *cmd, void *mconfig, int arg)
{
    loadshed_cfg *cfg = (loadshed_cfg *) mconfig;
    cfg->enabled = arg;
    return NULL;
}

static int check_loadshed(request_rec *r)
{
	loadshed_cfg *cfg;
	int             i, res;
	short_score     score_record;
	int             ready = 0;
	cfg = ap_get_module_config(r->per_dir_config, &loadshed_module);
	if (cfg->enabled) {
//		ap_sync_scoreboard_image();
		for (i = 0; i < HARD_SERVER_LIMIT; ++i) {
			score_record = ap_scoreboard_image->servers[i];
			res = score_record.status;
			if (res == SERVER_READY)
				ready++;
		}
		if (ready < 1) {
			ap_log_error(__FILE__, __LINE__, APLOG_NOERRNO, r->server, "shed request from %s.", r->connection->remote_ip);
			return HTTP_SERVICE_UNAVAILABLE;
		}
	}
	return DECLINED;
}

static const command_rec loadshed_cmds[] = {
	{"LoadShed", set_loadshed, NULL, OR_OPTIONS, FLAG, "set mod_loadshed on or off"},
	{NULL}
};

module MODULE_VAR_EXPORT loadshed_module =
{
    STANDARD_MODULE_STUFF,
    NULL,                       /* initializer */
    create_mconfig_for_directory,  /* create per-dir config */
    NULL,                       /* merge per-dir config */
    create_mconfig_for_server,  /* server config */
    NULL,                       /* merge server config */
    loadshed_cmds,               /* command table */
    NULL,                       /* handlers */
    NULL,                       /* filename translation */
    NULL,                       /* check_user_id */
    NULL,                       /* check auth */
    NULL,                       /* check access */
    NULL,                       /* type_checker */
    NULL,                       /* fixups */
    NULL,                       /* logger */
    NULL,                       /* header parser */
    NULL,                       /* child_init */
    NULL,                       /* child_exit */
    check_loadshed              /* post read-request */
};

/* eof */