/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "apr.h"
#include "apr_portable.h"
#include "apr_strings.h"
#include "apr_thread_proc.h"
#include "apr_signal.h"

#define APR_WANT_STDIO
#define APR_WANT_STRFUNC
#include "apr_want.h"

#if APR_HAVE_UNISTD_H
#include <unistd.h>
#endif
#if APR_HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif

#define CORE_PRIVATE

#include "ap_config.h"
#include "httpd.h"
#include "mpm_default.h"
#include "http_main.h"
#include "http_log.h"
#include "http_config.h"
#include "http_core.h"		/* for get_remote_host */
#include "http_connection.h"
#include "scoreboard.h"
#include "ap_mpm.h"
#include "unixd.h"
#include "mpm_common.h"
#include "ap_listen.h"
#include "ap_mmn.h"
#include "apr_poll.h"

#ifdef HAVE_BSTRING_H
#include <bstring.h>		/* for IRIX, FD_SET calls bzero() */
#endif
#ifdef HAVE_TIME_H
#include <time.h>
#endif
#ifdef HAVE_SYS_PROCESSOR_H
#include <sys/processor.h> /* for bindprocessor() */
#endif

#include <signal.h>
#include <sys/times.h>

/* Limit on the total --- clients will be locked out if more servers than
 * this are needed.  It is intended solely to keep the server from crashing
 * when things get out of hand.
 *
 * We keep a hard maximum number of servers, for two reasons --- first off,
 * in case something goes seriously wrong, we want to stop the fork bomb
 * short of actually crashing the machine we're running on by filling some
 * kernel table.  Secondly, it keeps the size of the scoreboard file small
 * enough that we can read the whole thing without worrying too much about
 * the overhead.
 */
#ifndef DEFAULT_SERVER_LIMIT
#define DEFAULT_SERVER_LIMIT 256
#endif

/* Admin can't tune ServerLimit beyond MAX_SERVER_LIMIT.  We want
 * some sort of compile-time limit to help catch typos.
 */
#ifndef MAX_SERVER_LIMIT
#define MAX_SERVER_LIMIT 20000
#endif

#ifndef HARD_THREAD_LIMIT
#define HARD_THREAD_LIMIT 1
#endif

/* config globals */

int ap_threads_per_child=0;         /* Worker threads per child */
static apr_proc_mutex_t *accept_mutex;
static int ap_daemons_to_start=0;
static int ap_daemons_min_free=0;
static int ap_daemons_max_free=0;
static int ap_daemons_limit=0;      /* MaxClients */
static int server_limit = DEFAULT_SERVER_LIMIT;
static int first_server_limit;
static int changed_limit_at_restart;
static int mpm_state = AP_MPMQ_STARTING;
static ap_pod_t *pod;

/*
 * The max child slot ever assigned, preserved across restarts.  Necessary
 * to deal with MaxClients changes across AP_SIG_GRACEFUL restarts.  We 
 * use this value to optimize routines that have to scan the entire scoreboard.
 */
int ap_max_daemons_limit = -1;
server_rec *ap_server_conf;

/* one_process --- debugging mode variable; can be set from the command line
 * with the -X flag.  If set, this gets you the child_main loop running
 * in the process which originally started up (no detach, no make_child),
 * which is a pretty nice debugging environment.  (You'll get a SIGHUP
 * early in standalone_main; just continue through.  This is the server
 * trying to kill off any child processes which it might have lying
 * around --- Apache doesn't keep track of their pids, it just sends
 * SIGHUP to the process group, ignoring it in the root process.
 * Continue through and you'll be fine.).
 */

static int one_process = 0;

static apr_pool_t *pconf;		/* Pool for config stuff */
static apr_pool_t *pchild;		/* Pool for httpd child stuff */

static pid_t ap_my_pid;	/* it seems silly to call getpid all the time */
static pid_t parent_pid;
#ifndef MULTITHREAD
static int my_child_num;
#endif
ap_generation_t volatile ap_my_generation=0;

#ifdef TPF
int tpf_child = 0;
char tpf_server_name[INETD_SERVNAME_LENGTH+1];
#endif /* TPF */

static int die_now = 0;

#ifdef GPROF
/* 
 * change directory for gprof to plop the gmon.out file
 * configure in httpd.conf:
 * GprofDir $RuntimeDir/   -> $ServerRoot/$RuntimeDir/gmon.out
 * GprofDir $RuntimeDir/%  -> $ServerRoot/$RuntimeDir/gprof.$pid/gmon.out
 */
static void chdir_for_gprof(void)
{
    core_server_config *sconf = 
	ap_get_module_config(ap_server_conf->module_config, &core_module);    
    char *dir = sconf->gprof_dir;
    const char *use_dir;

    if(dir) {
        apr_status_t res;
	char buf[512];
	int len = strlen(sconf->gprof_dir) - 1;
	if(*(dir + len) == '%') {
	    dir[len] = '\0';
	    apr_snprintf(buf, sizeof(buf), "%sgprof.%d", dir, (int)getpid());
	} 
	use_dir = ap_server_root_relative(pconf, buf[0] ? buf : dir);
	res = apr_dir_make(use_dir, 0755, pconf);
	if(res != APR_SUCCESS && !APR_STATUS_IS_EEXIST(res)) {
	    ap_log_error(APLOG_MARK, APLOG_ERR, errno, ap_server_conf,
			 "gprof: error creating directory %s", dir);
	}
    }
    else {
	use_dir = ap_server_root_relative(pconf, DEFAULT_REL_RUNTIMEDIR);
    }

    chdir(use_dir);
}
#else
#define chdir_for_gprof()
#endif

/* XXX - I don't know if TPF will ever use this module or not, so leave
 * the ap_check_signals calls in but disable them - manoj */
#define ap_check_signals() 

/* a clean exit from a child with proper cleanup */
static void clean_child_exit(int code) __attribute__ ((noreturn));
static void clean_child_exit(int code)
{
    mpm_state = AP_MPMQ_STOPPING;

    if (pchild) {
	apr_pool_destroy(pchild);
    }
    ap_mpm_pod_close(pod);
    chdir_for_gprof();
    exit(code);
}

static void accept_mutex_on(void)
{
    apr_status_t rv = apr_proc_mutex_lock(accept_mutex);
    if (rv != APR_SUCCESS) {
        const char *msg = "couldn't grab the accept mutex";

        if (ap_my_generation != 
            ap_scoreboard_image->global->running_generation) {
            ap_log_error(APLOG_MARK, APLOG_DEBUG, rv, NULL, msg);
            clean_child_exit(0);
        }
        else {
            ap_log_error(APLOG_MARK, APLOG_EMERG, rv, NULL, msg);
            exit(APEXIT_CHILDFATAL);
        }
    }
}

static void accept_mutex_off(void)
{
    apr_status_t rv = apr_proc_mutex_unlock(accept_mutex);
    if (rv != APR_SUCCESS) {
        const char *msg = "couldn't release the accept mutex";

        if (ap_my_generation != 
            ap_scoreboard_image->global->running_generation) {
            ap_log_error(APLOG_MARK, APLOG_DEBUG, rv, NULL, msg);
            /* don't exit here... we have a connection to
             * process, after which point we'll see that the
             * generation changed and we'll exit cleanly
             */
        }
        else {
            ap_log_error(APLOG_MARK, APLOG_EMERG, rv, NULL, msg);
            exit(APEXIT_CHILDFATAL);
        }
    }
}

/* On some architectures it's safe to do unserialized accept()s in the single
 * Listen case.  But it's never safe to do it in the case where there's
 * multiple Listen statements.  Define SINGLE_LISTEN_UNSERIALIZED_ACCEPT
 * when it's safe in the single Listen case.
 */
#ifdef SINGLE_LISTEN_UNSERIALIZED_ACCEPT
#define SAFE_ACCEPT(stmt) do {if (ap_listeners->next) {stmt;}} while(0)
#else
#define SAFE_ACCEPT(stmt) do {stmt;} while(0)
#endif

AP_DECLARE(apr_status_t) ap_mpm_query(int query_code, int *result)
{
    switch(query_code){
        case AP_MPMQ_MAX_DAEMON_USED:
            *result = ap_daemons_limit;
            return APR_SUCCESS;
        case AP_MPMQ_IS_THREADED:
            *result = AP_MPMQ_NOT_SUPPORTED;
            return APR_SUCCESS;
        case AP_MPMQ_IS_FORKED:
            *result = AP_MPMQ_DYNAMIC;
            return APR_SUCCESS;
        case AP_MPMQ_HARD_LIMIT_DAEMONS:
            *result = server_limit;
            return APR_SUCCESS;
        case AP_MPMQ_HARD_LIMIT_THREADS:
            *result = HARD_THREAD_LIMIT;
            return APR_SUCCESS;
        case AP_MPMQ_MAX_THREADS:
            *result = 0;
            return APR_SUCCESS;
        case AP_MPMQ_MIN_SPARE_DAEMONS:
            *result = ap_daemons_min_free;
            return APR_SUCCESS;
        case AP_MPMQ_MIN_SPARE_THREADS:
            *result = 0;
            return APR_SUCCESS;
        case AP_MPMQ_MAX_SPARE_DAEMONS:
            *result = ap_daemons_max_free;
            return APR_SUCCESS;
        case AP_MPMQ_MAX_SPARE_THREADS:
            *result = 0;
            return APR_SUCCESS;
        case AP_MPMQ_MAX_REQUESTS_DAEMON:
            *result = ap_max_requests_per_child;
            return APR_SUCCESS;
        case AP_MPMQ_MAX_DAEMONS:
            *result = server_limit;
            return APR_SUCCESS;
        case AP_MPMQ_MPM_STATE:
            *result = mpm_state;
            return APR_SUCCESS;
    }
    return APR_ENOTIMPL;
}

#if defined(NEED_WAITPID)
/*
   Systems without a real waitpid sometimes lose a child's exit while waiting
   for another.  Search through the scoreboard for missing children.
 */
int reap_children(int *exitcode, apr_exit_why_e *status)
{
    int n, pid;

    for (n = 0; n < ap_max_daemons_limit; ++n) {
	if (ap_scoreboard_image->servers[n][0].status != SERVER_DEAD &&
		kill((pid = ap_scoreboard_image->parent[n].pid), 0) == -1) {
	    ap_update_child_status_from_indexes(n, 0, SERVER_DEAD, NULL);
	    /* just mark it as having a successful exit status */
            *status = APR_PROC_EXIT;
            *exitcode = 0;
	    return(pid);
	}
    }
    return 0;
}
#endif

/*****************************************************************
 * Connection structures and accounting...
 */

static void just_die(int sig)
{
    clean_child_exit(0);
}

/* volatile just in case */
static int volatile shutdown_pending;
static int volatile restart_pending;
static int volatile is_graceful;

static void sig_term(int sig)
{
    if (shutdown_pending == 1) {
	/* Um, is this _probably_ not an error, if the user has
	 * tried to do a shutdown twice quickly, so we won't
	 * worry about reporting it.
	 */
	return;
    }
    shutdown_pending = 1;
}

/* restart() is the signal handler for SIGHUP and AP_SIG_GRACEFUL
 * in the parent process, unless running in ONE_PROCESS mode
 */
static void restart(int sig)
{
    if (restart_pending == 1) {
	/* Probably not an error - don't bother reporting it */
	return;
    }
    restart_pending = 1;
    is_graceful = (sig == AP_SIG_GRACEFUL);
}

static void set_signals(void)
{
#ifndef NO_USE_SIGACTION
    struct sigaction sa;
#endif

    if (!one_process) {
        ap_fatal_signal_setup(ap_server_conf, pconf);
    }

#ifndef NO_USE_SIGACTION
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;

    sa.sa_handler = sig_term;
    if (sigaction(SIGTERM, &sa, NULL) < 0)
	ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf, "sigaction(SIGTERM)");
#ifdef SIGINT
    if (sigaction(SIGINT, &sa, NULL) < 0)
        ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf, "sigaction(SIGINT)");
#endif
#ifdef SIGXCPU
    sa.sa_handler = SIG_DFL;
    if (sigaction(SIGXCPU, &sa, NULL) < 0)
	ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf, "sigaction(SIGXCPU)");
#endif
#ifdef SIGXFSZ
    sa.sa_handler = SIG_DFL;
    if (sigaction(SIGXFSZ, &sa, NULL) < 0)
	ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf, "sigaction(SIGXFSZ)");
#endif
#ifdef SIGPIPE
    sa.sa_handler = SIG_IGN;
    if (sigaction(SIGPIPE, &sa, NULL) < 0)
	ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf, "sigaction(SIGPIPE)");
#endif

    /* we want to ignore HUPs and AP_SIG_GRACEFUL while we're busy 
     * processing one */
    sigaddset(&sa.sa_mask, SIGHUP);
    sigaddset(&sa.sa_mask, AP_SIG_GRACEFUL);
    sa.sa_handler = restart;
    if (sigaction(SIGHUP, &sa, NULL) < 0)
	ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf, "sigaction(SIGHUP)");
    if (sigaction(AP_SIG_GRACEFUL, &sa, NULL) < 0)
        ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf, "sigaction(" AP_SIG_GRACEFUL_STRING ")");
#else
    if (!one_process) {
#ifdef SIGXCPU
	apr_signal(SIGXCPU, SIG_DFL);
#endif /* SIGXCPU */
#ifdef SIGXFSZ
	apr_signal(SIGXFSZ, SIG_DFL);
#endif /* SIGXFSZ */
    }

    apr_signal(SIGTERM, sig_term);
#ifdef SIGHUP
    apr_signal(SIGHUP, restart);
#endif /* SIGHUP */
#ifdef AP_SIG_GRACEFUL
    apr_signal(AP_SIG_GRACEFUL, restart);
#endif /* AP_SIG_GRACEFUL */
#ifdef SIGPIPE
    apr_signal(SIGPIPE, SIG_IGN);
#endif /* SIGPIPE */

#endif
}

/*****************************************************************
 * Child process main loop.
 * The following vars are static to avoid getting clobbered by longjmp();
 * they are really private to child_main.
 */

static int requests_this_child;
static int num_listensocks = 0;
static ap_listen_rec *listensocks;

int ap_graceful_stop_signalled(void)
{
    /* not ever called anymore... */
    return 0;
}


static void child_main(int child_num_arg)
{
    apr_pool_t *ptrans;
    apr_allocator_t *allocator;
    conn_rec *current_conn;
    apr_status_t status = APR_EINIT;
    int i;
    ap_listen_rec *lr;
    int curr_pollfd, last_pollfd = 0;
    apr_pollfd_t *pollset;
    int offset;
    void *csd;
    ap_sb_handle_t *sbh;
    apr_status_t rv;
    apr_bucket_alloc_t *bucket_alloc;

    mpm_state = AP_MPMQ_STARTING; /* for benefit of any hooks that run as this
                                  * child initializes
                                  */
    
    my_child_num = child_num_arg;
    ap_my_pid = getpid();
    csd = NULL;
    requests_this_child = 0;

    ap_fatal_signal_child_setup(ap_server_conf);

    /* Get a sub context for global allocations in this child, so that
     * we can have cleanups occur when the child exits.
     */
    apr_allocator_create(&allocator);
    apr_allocator_max_free_set(allocator, ap_max_mem_free);
    apr_pool_create_ex(&pchild, pconf, NULL, allocator);
    apr_allocator_owner_set(allocator, pchild);

    apr_pool_create(&ptrans, pchild);
    apr_pool_tag(ptrans, "transaction");

    /* needs to be done before we switch UIDs so we have permissions */
    ap_reopen_scoreboard(pchild, NULL, 0);
    rv = apr_proc_mutex_child_init(&accept_mutex, ap_lock_fname, pchild);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_EMERG, rv, ap_server_conf,
                     "Couldn't initialize cross-process lock in child");
        clean_child_exit(APEXIT_CHILDFATAL);
    }

    if (unixd_setup_child()) {
	clean_child_exit(APEXIT_CHILDFATAL);
    }

    ap_run_child_init(pchild, ap_server_conf);

    ap_create_sb_handle(&sbh, pchild, my_child_num, 0);

    (void) ap_update_child_status(sbh, SERVER_READY, (request_rec *) NULL);

    /* Set up the pollfd array */
    listensocks = apr_pcalloc(pchild,
                            sizeof(*listensocks) * (num_listensocks));
    for (lr = ap_listeners, i = 0; i < num_listensocks; lr = lr->next, i++) {
        listensocks[i].accept_func = lr->accept_func;
        listensocks[i].sd = lr->sd;
    }

    pollset = apr_palloc(pchild, sizeof(*pollset) * num_listensocks);
    pollset[0].p = pchild;
    for (i = 0; i < num_listensocks; i++) {
        pollset[i].desc.s = listensocks[i].sd;
        pollset[i].desc_type = APR_POLL_SOCKET;
        pollset[i].reqevents = APR_POLLIN;
    }

    mpm_state = AP_MPMQ_RUNNING;
    
    bucket_alloc = apr_bucket_alloc_create(pchild);

    while (!die_now) {
	/*
	 * (Re)initialize this child to a pre-connection state.
	 */

	current_conn = NULL;

	apr_pool_clear(ptrans);

	if ((ap_max_requests_per_child > 0
	     && requests_this_child++ >= ap_max_requests_per_child)) {
	    clean_child_exit(0);
	}

	(void) ap_update_child_status(sbh, SERVER_READY, (request_rec *) NULL);

	/*
	 * Wait for an acceptable connection to arrive.
	 */

	/* Lock around "accept", if necessary */
	SAFE_ACCEPT(accept_mutex_on());

        if (num_listensocks == 1) {
            offset = 0;
        }
        else {
            /* multiple listening sockets - need to poll */
	    for (;;) {
                apr_status_t ret;
                apr_int32_t n;

                ret = apr_poll(pollset, num_listensocks, &n, -1);
                if (ret != APR_SUCCESS) {
                    if (APR_STATUS_IS_EINTR(ret)) {
                        continue;
                    }
    	            /* Single Unix documents select as returning errnos
    	             * EBADF, EINTR, and EINVAL... and in none of those
    	             * cases does it make sense to continue.  In fact
    	             * on Linux 2.0.x we seem to end up with EFAULT
    	             * occasionally, and we'd loop forever due to it.
    	             */
    	            ap_log_error(APLOG_MARK, APLOG_ERR, ret, ap_server_conf,
                             "apr_poll: (listen)");
    	            clean_child_exit(1);
                }
                /* find a listener */
                curr_pollfd = last_pollfd;
                do {
                    curr_pollfd++;
                    if (curr_pollfd >= num_listensocks) {
                        curr_pollfd = 0;
                    }
                    /* XXX: Should we check for POLLERR? */
                    if (pollset[curr_pollfd].rtnevents & APR_POLLIN) {
                        last_pollfd = curr_pollfd;
                        offset = curr_pollfd;
                        goto got_fd;
                    }
                } while (curr_pollfd != last_pollfd);

                continue;
            }
        }
    got_fd:
	/* if we accept() something we don't want to die, so we have to
	 * defer the exit
	 */
        status = listensocks[offset].accept_func(&csd, 
                                                 &listensocks[offset], ptrans);
        SAFE_ACCEPT(accept_mutex_off());	/* unlock after "accept" */

        if (status == APR_EGENERAL) {
            /* resource shortage or should-not-occur occured */
            clean_child_exit(1);
        }
        else if (status != APR_SUCCESS) {
            continue;
        }

	/*
	 * We now have a connection, so set it up with the appropriate
	 * socket options, file descriptors, and read/write buffers.
	 */

	current_conn = ap_run_create_connection(ptrans, ap_server_conf, csd, my_child_num, sbh, bucket_alloc);
        if (current_conn) {
            ap_process_connection(current_conn, csd);
            ap_lingering_close(current_conn);
        }
        
        /* Check the pod and the generation number after processing a
         * connection so that we'll go away if a graceful restart occurred
         * while we were processing the connection or we are the lucky
         * idle server process that gets to die.
         */
        if (ap_mpm_pod_check(pod) == APR_SUCCESS) { /* selected as idle? */
            die_now = 1;
        }
        else if (ap_my_generation !=
                 ap_scoreboard_image->global->running_generation) { /* restart? */
            /* yeah, this could be non-graceful restart, in which case the
             * parent will kill us soon enough, but why bother checking?
             */
            die_now = 1;
        }
    }
    clean_child_exit(0);
}


static int make_child(server_rec *s, int slot)
{
    int pid;

    if (slot + 1 > ap_max_daemons_limit) {
	ap_max_daemons_limit = slot + 1;
    }

    if (one_process) {
	apr_signal(SIGHUP, just_die);
        /* Don't catch AP_SIG_GRACEFUL in ONE_PROCESS mode :) */
	apr_signal(SIGINT, just_die);
#ifdef SIGQUIT
	apr_signal(SIGQUIT, SIG_DFL);
#endif
	apr_signal(SIGTERM, just_die);
	child_main(slot);
    }

    (void) ap_update_child_status_from_indexes(slot, 0, SERVER_STARTING,
                                               (request_rec *) NULL);


#ifdef _OSD_POSIX
    /* BS2000 requires a "special" version of fork() before a setuid() call */
    if ((pid = os_fork(unixd_config.user_name)) == -1) {
#elif defined(TPF)
    if ((pid = os_fork(s, slot)) == -1) {
#else
    if ((pid = fork()) == -1) {
#endif
	ap_log_error(APLOG_MARK, APLOG_ERR, errno, s, "fork: Unable to fork new process");

	/* fork didn't succeed. Fix the scoreboard or else
	 * it will say SERVER_STARTING forever and ever
	 */
	(void) ap_update_child_status_from_indexes(slot, 0, SERVER_DEAD,
                                                   (request_rec *) NULL);

	/* In case system resources are maxxed out, we don't want
	   Apache running away with the CPU trying to fork over and
	   over and over again. */
	sleep(10);

	return -1;
    }

    if (!pid) {
#ifdef HAVE_BINDPROCESSOR
        /* by default AIX binds to a single processor
         * this bit unbinds children which will then bind to another cpu
         */
	int status = bindprocessor(BINDPROCESS, (int)getpid(), 
				   PROCESSOR_CLASS_ANY);
	if (status != OK) {
	    ap_log_error(APLOG_MARK, APLOG_WARNING, errno, 
                         ap_server_conf, "processor unbind failed %d", status);
	}
#endif
	RAISE_SIGSTOP(MAKE_CHILD);
        AP_MONCONTROL(1);
        /* Disable the parent's signal handlers and set up proper handling in
         * the child.
	 */
	apr_signal(SIGHUP, just_die);
	apr_signal(SIGTERM, just_die);
        /* The child process doesn't do anything for AP_SIG_GRACEFUL.  
         * Instead, the pod is used for signalling graceful restart.
         */
        apr_signal(AP_SIG_GRACEFUL, SIG_IGN);
	child_main(slot);
    }

    ap_scoreboard_image->parent[slot].pid = pid;

    return 0;
}


/* start up a bunch of children */
static void startup_children(int number_to_start)
{
    int i;

    for (i = 0; number_to_start && i < ap_daemons_limit; ++i) {
	if (ap_scoreboard_image->servers[i][0].status != SERVER_DEAD) {
	    continue;
	}
	if (make_child(ap_server_conf, i) < 0) {
	    break;
	}
	--number_to_start;
    }
}


/*
 * idle_spawn_rate is the number of children that will be spawned on the
 * next maintenance cycle if there aren't enough idle servers.  It is
 * doubled up to MAX_SPAWN_RATE, and reset only when a cycle goes by
 * without the need to spawn.
 */
static int idle_spawn_rate = 1;
#ifndef MAX_SPAWN_RATE
#define MAX_SPAWN_RATE	(32)
#endif
static int hold_off_on_exponential_spawning;

static void perform_idle_server_maintenance(apr_pool_t *p)
{
    int i;
    int to_kill;
    int idle_count;
    worker_score *ws;
    int free_length;
    int free_slots[MAX_SPAWN_RATE];
    int last_non_dead;
    int total_non_dead;

    /* initialize the free_list */
    free_length = 0;

    to_kill = -1;
    idle_count = 0;
    last_non_dead = -1;
    total_non_dead = 0;

    for (i = 0; i < ap_daemons_limit; ++i) {
	int status;

	if (i >= ap_max_daemons_limit && free_length == idle_spawn_rate)
	    break;
	ws = &ap_scoreboard_image->servers[i][0];
	status = ws->status;
	if (status == SERVER_DEAD) {
	    /* try to keep children numbers as low as possible */
	    if (free_length < idle_spawn_rate) {
		free_slots[free_length] = i;
		++free_length;
	    }
	}
	else {
	    /* We consider a starting server as idle because we started it
	     * at least a cycle ago, and if it still hasn't finished starting
	     * then we're just going to swamp things worse by forking more.
	     * So we hopefully won't need to fork more if we count it.
	     * This depends on the ordering of SERVER_READY and SERVER_STARTING.
	     */
	    if (status <= SERVER_READY) {
		++ idle_count;
		/* always kill the highest numbered child if we have to...
		 * no really well thought out reason ... other than observing
		 * the server behaviour under linux where lower numbered children
		 * tend to service more hits (and hence are more likely to have
		 * their data in cpu caches).
		 */
		to_kill = i;
	    }

	    ++total_non_dead;
	    last_non_dead = i;
	}
    }
    ap_max_daemons_limit = last_non_dead + 1;
    if (idle_count > ap_daemons_max_free) {
	/* kill off one child... we use the pod because that'll cause it to
	 * shut down gracefully, in case it happened to pick up a request
	 * while we were counting
	 */
	ap_mpm_pod_signal(pod);
	idle_spawn_rate = 1;
    }
    else if (idle_count < ap_daemons_min_free) {
	/* terminate the free list */
	if (free_length == 0) {
	    /* only report this condition once */
	    static int reported = 0;

	    if (!reported) {
		ap_log_error(APLOG_MARK, APLOG_ERR, 0, ap_server_conf,
			    "server reached MaxClients setting, consider"
			    " raising the MaxClients setting");
		reported = 1;
	    }
	    idle_spawn_rate = 1;
	}
	else {
	    if (idle_spawn_rate >= 8) {
		ap_log_error(APLOG_MARK, APLOG_INFO, 0, ap_server_conf,
		    "server seems busy, (you may need "
		    "to increase StartServers, or Min/MaxSpareServers), "
		    "spawning %d children, there are %d idle, and "
		    "%d total children", idle_spawn_rate,
		    idle_count, total_non_dead);
	    }
	    for (i = 0; i < free_length; ++i) {
#ifdef TPF
        if (make_child(ap_server_conf, free_slots[i]) == -1) {
            if(free_length == 1) {
                shutdown_pending = 1;
                ap_log_error(APLOG_MARK, APLOG_EMERG, 0, ap_server_conf,
                "No active child processes: shutting down");
            }
        }
#else
		make_child(ap_server_conf, free_slots[i]);
#endif /* TPF */
	    }
	    /* the next time around we want to spawn twice as many if this
	     * wasn't good enough, but not if we've just done a graceful
	     */
	    if (hold_off_on_exponential_spawning) {
		--hold_off_on_exponential_spawning;
	    }
	    else if (idle_spawn_rate < MAX_SPAWN_RATE) {
		idle_spawn_rate *= 2;
	    }
	}
    }
    else {
	idle_spawn_rate = 1;
    }
}

/*****************************************************************
 * Executive routines.
 */

int ap_mpm_run(apr_pool_t *_pconf, apr_pool_t *plog, server_rec *s)
{
    int index;
    int remaining_children_to_start;
    apr_status_t rv;

    ap_log_pid(pconf, ap_pid_fname);

    first_server_limit = server_limit;
    if (changed_limit_at_restart) {
        ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s,
                     "WARNING: Attempt to change ServerLimit "
                     "ignored during restart");
        changed_limit_at_restart = 0;
    }

    /* Initialize cross-process accept lock */
    ap_lock_fname = apr_psprintf(_pconf, "%s.%" APR_PID_T_FMT,
                                 ap_server_root_relative(_pconf, ap_lock_fname),
                                 ap_my_pid);

    rv = apr_proc_mutex_create(&accept_mutex, ap_lock_fname, 
                               ap_accept_lock_mech, _pconf);
    if (rv != APR_SUCCESS) {
        ap_log_error(APLOG_MARK, APLOG_EMERG, rv, s,
                     "Couldn't create accept lock");
        mpm_state = AP_MPMQ_STOPPING;
        return 1;
    }

#if APR_USE_SYSVSEM_SERIALIZE
    if (ap_accept_lock_mech == APR_LOCK_DEFAULT || 
        ap_accept_lock_mech == APR_LOCK_SYSVSEM) {
#else
    if (ap_accept_lock_mech == APR_LOCK_SYSVSEM) {
#endif
        rv = unixd_set_proc_mutex_perms(accept_mutex);
        if (rv != APR_SUCCESS) {
            ap_log_error(APLOG_MARK, APLOG_EMERG, rv, s,
                         "Couldn't set permissions on cross-process lock; "
                         "check User and Group directives");
            mpm_state = AP_MPMQ_STOPPING;
            return 1;
        }
    }

    if (!is_graceful) {
        if (ap_run_pre_mpm(s->process->pool, SB_SHARED) != OK) {
            mpm_state = AP_MPMQ_STOPPING;
            return 1;
        }
        /* fix the generation number in the global score; we just got a new,
         * cleared scoreboard
         */
        ap_scoreboard_image->global->running_generation = ap_my_generation;
    }

    set_signals();

    if (one_process) {
        AP_MONCONTROL(1);
    }

    if (ap_daemons_max_free < ap_daemons_min_free + 1)	/* Don't thrash... */
	ap_daemons_max_free = ap_daemons_min_free + 1;

    /* If we're doing a graceful_restart then we're going to see a lot
	* of children exiting immediately when we get into the main loop
	* below (because we just sent them AP_SIG_GRACEFUL).  This happens pretty
	* rapidly... and for each one that exits we'll start a new one until
	* we reach at least daemons_min_free.  But we may be permitted to
	* start more than that, so we'll just keep track of how many we're
	* supposed to start up without the 1 second penalty between each fork.
	*/
    remaining_children_to_start = ap_daemons_to_start;
    if (remaining_children_to_start > ap_daemons_limit) {
	remaining_children_to_start = ap_daemons_limit;
    }
    if (!is_graceful) {
	startup_children(remaining_children_to_start);
	remaining_children_to_start = 0;
    }
    else {
	/* give the system some time to recover before kicking into
	    * exponential mode */
	hold_off_on_exponential_spawning = 10;
    }

    ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, ap_server_conf,
		"%s configured -- resuming normal operations",
		ap_get_server_version());
    ap_log_error(APLOG_MARK, APLOG_INFO, 0, ap_server_conf,
		"Server built: %s", ap_get_server_built());
#ifdef AP_MPM_WANT_SET_ACCEPT_LOCK_MECH
    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, ap_server_conf,
		"AcceptMutex: %s (default: %s)",
		apr_proc_mutex_name(accept_mutex),
		apr_proc_mutex_defname());
#endif
    restart_pending = shutdown_pending = 0;

    mpm_state = AP_MPMQ_RUNNING;
    
    while (!restart_pending && !shutdown_pending) {
	int child_slot;
        apr_exit_why_e exitwhy;
	int status, processed_status;
        /* this is a memory leak, but I'll fix it later. */
	apr_proc_t pid;

        ap_wait_or_timeout(&exitwhy, &status, &pid, pconf);

	/* XXX: if it takes longer than 1 second for all our children
	 * to start up and get into IDLE state then we may spawn an
	 * extra child
	 */
	if (pid.pid != -1) {
            processed_status = ap_process_child_status(&pid, exitwhy, status);
            if (processed_status == APEXIT_CHILDFATAL) {
                mpm_state = AP_MPMQ_STOPPING;
                return 1;
            }

	    /* non-fatal death... note that it's gone in the scoreboard. */
	    child_slot = find_child_by_pid(&pid);
	    if (child_slot >= 0) {
		(void) ap_update_child_status_from_indexes(child_slot, 0, SERVER_DEAD,
                                                           (request_rec *) NULL);
                if (processed_status == APEXIT_CHILDSICK) {
                    /* child detected a resource shortage (E[NM]FILE, ENOBUFS, etc)
                     * cut the fork rate to the minimum 
                     */
                    idle_spawn_rate = 1; 
                }
                else if (remaining_children_to_start
		    && child_slot < ap_daemons_limit) {
		    /* we're still doing a 1-for-1 replacement of dead
			* children with new children
			*/
		    make_child(ap_server_conf, child_slot);
		    --remaining_children_to_start;
		}
#if APR_HAS_OTHER_CHILD
	    }
	    else if (apr_proc_other_child_read(&pid, status) == 0) {
		/* handled */
#endif
	    }
	    else if (is_graceful) {
		/* Great, we've probably just lost a slot in the
		    * scoreboard.  Somehow we don't know about this
		    * child.
		    */
		ap_log_error(APLOG_MARK, APLOG_WARNING, 
                            0, ap_server_conf,
			    "long lost child came home! (pid %ld)", (long)pid.pid);
	    }
	    /* Don't perform idle maintenance when a child dies,
		* only do it when there's a timeout.  Remember only a
		* finite number of children can die, and it's pretty
		* pathological for a lot to die suddenly.
		*/
	    continue;
	}
	else if (remaining_children_to_start) {
	    /* we hit a 1 second timeout in which none of the previous
		* generation of children needed to be reaped... so assume
		* they're all done, and pick up the slack if any is left.
		*/
	    startup_children(remaining_children_to_start);
	    remaining_children_to_start = 0;
	    /* In any event we really shouldn't do the code below because
		* few of the servers we just started are in the IDLE state
		* yet, so we'd mistakenly create an extra server.
		*/
	    continue;
	}

	perform_idle_server_maintenance(pconf);
#ifdef TPF
    shutdown_pending = os_check_server(tpf_server_name);
    ap_check_signals();
    sleep(1);
#endif /*TPF */
    }

    mpm_state = AP_MPMQ_STOPPING;

    if (shutdown_pending) {
	/* Time to gracefully shut down:
	 * Kill child processes, tell them to call child_exit, etc...
	 */
	if (unixd_killpg(getpgrp(), SIGTERM) < 0) {
	    ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf, "killpg SIGTERM");
	}
	ap_reclaim_child_processes(1);		/* Start with SIGTERM */

	/* cleanup pid file on normal shutdown */
	{
	    const char *pidfile = NULL;
	    pidfile = ap_server_root_relative (pconf, ap_pid_fname);
	    if ( pidfile != NULL && unlink(pidfile) == 0)
		ap_log_error(APLOG_MARK, APLOG_INFO,
				0, ap_server_conf,
				"removed PID file %s (pid=%ld)",
				pidfile, (long)getpid());
	}

	ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, ap_server_conf,
		    "caught SIGTERM, shutting down");
	return 1;
    }

    /* we've been told to restart */
    apr_signal(SIGHUP, SIG_IGN);
    if (one_process) {
	/* not worth thinking about */
	return 1;
    }

    /* advance to the next generation */
    /* XXX: we really need to make sure this new generation number isn't in
     * use by any of the children.
     */
    ++ap_my_generation;
    ap_scoreboard_image->global->running_generation = ap_my_generation;
    
    if (is_graceful) {
	ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, ap_server_conf,
		    "Graceful restart requested, doing restart");

	/* kill off the idle ones */
        ap_mpm_pod_killpg(pod, ap_max_daemons_limit);

	/* This is mostly for debugging... so that we know what is still
	    * gracefully dealing with existing request.  This will break
	    * in a very nasty way if we ever have the scoreboard totally
	    * file-based (no shared memory)
	    */
	for (index = 0; index < ap_daemons_limit; ++index) {
	    if (ap_scoreboard_image->servers[index][0].status != SERVER_DEAD) {
		ap_scoreboard_image->servers[index][0].status = SERVER_GRACEFUL;
	    }
	}
    }
    else {
	/* Kill 'em off */
	if (unixd_killpg(getpgrp(), SIGHUP) < 0) {
	    ap_log_error(APLOG_MARK, APLOG_WARNING, errno, ap_server_conf, "killpg SIGHUP");
	}
	ap_reclaim_child_processes(0);		/* Not when just starting up */
	ap_log_error(APLOG_MARK, APLOG_NOTICE, 0, ap_server_conf,
		    "SIGHUP received.  Attempting to restart");
    }

    return 0;
}

/* This really should be a post_config hook, but the error log is already
 * redirected by that point, so we need to do this in the open_logs phase.
 */
static int prefork_open_logs(apr_pool_t *p, apr_pool_t *plog, apr_pool_t *ptemp, server_rec *s)
{
    apr_status_t rv;

    pconf = p;
    ap_server_conf = s;

    if ((num_listensocks = ap_setup_listeners(ap_server_conf)) < 1) {
        ap_log_error(APLOG_MARK, APLOG_ALERT|APLOG_STARTUP, 0, 
                     NULL, "no listening sockets available, shutting down");
	return DONE;
    }

    if ((rv = ap_mpm_pod_open(pconf, &pod))) {
        ap_log_error(APLOG_MARK, APLOG_CRIT|APLOG_STARTUP, rv, NULL,
		"Could not open pipe-of-death.");
        return DONE;
    }
    return OK;
}

static int prefork_pre_config(apr_pool_t *p, apr_pool_t *plog, apr_pool_t *ptemp)
{
    static int restart_num = 0;
    int no_detach, debug, foreground;
    apr_status_t rv;

    mpm_state = AP_MPMQ_STARTING;

    debug = ap_exists_config_define("DEBUG");

    if (debug) {
        foreground = one_process = 1;
        no_detach = 0;
    }
    else
    {
        no_detach = ap_exists_config_define("NO_DETACH");
        one_process = ap_exists_config_define("ONE_PROCESS");
        foreground = ap_exists_config_define("FOREGROUND");
    }

    /* sigh, want this only the second time around */
    if (restart_num++ == 1) {
	is_graceful = 0;

        if (!one_process && !foreground) {
            rv = apr_proc_detach(no_detach ? APR_PROC_DETACH_FOREGROUND
                                           : APR_PROC_DETACH_DAEMONIZE);
            if (rv != APR_SUCCESS) {
                ap_log_error(APLOG_MARK, APLOG_CRIT, rv, NULL,
                             "apr_proc_detach failed");
                return HTTP_INTERNAL_SERVER_ERROR;
            }
        }

	parent_pid = ap_my_pid = getpid();
    }

    unixd_pre_config(ptemp);
    ap_listen_pre_config();
    ap_daemons_to_start = DEFAULT_START_DAEMON;
    ap_daemons_min_free = DEFAULT_MIN_FREE_DAEMON;
    ap_daemons_max_free = DEFAULT_MAX_FREE_DAEMON;
    ap_daemons_limit = server_limit;
    ap_pid_fname = DEFAULT_PIDLOG;
    ap_lock_fname = DEFAULT_LOCKFILE;
    ap_max_requests_per_child = DEFAULT_MAX_REQUESTS_PER_CHILD;
    ap_extended_status = 0;
#ifdef AP_MPM_WANT_SET_MAX_MEM_FREE
	ap_max_mem_free = APR_ALLOCATOR_MAX_FREE_UNLIMITED;
#endif

    apr_cpystrn(ap_coredump_dir, ap_server_root, sizeof(ap_coredump_dir));

    return OK;
}

static void prefork_hooks(apr_pool_t *p)
{
    /* The prefork open_logs phase must run before the core's, or stderr
     * will be redirected to a file, and the messages won't print to the
     * console.
     */
    static const char *const aszSucc[] = {"core.c", NULL};

#ifdef AUX3
    (void) set42sig();
#endif

    ap_hook_open_logs(prefork_open_logs, NULL, aszSucc, APR_HOOK_MIDDLE);
    /* we need to set the MPM state before other pre-config hooks use MPM query
     * to retrieve it, so register as REALLY_FIRST
     */
    ap_hook_pre_config(prefork_pre_config, NULL, NULL, APR_HOOK_REALLY_FIRST);
}

static const char *set_daemons_to_start(cmd_parms *cmd, void *dummy, const char *arg) 
{
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    ap_daemons_to_start = atoi(arg);
    return NULL;
}

static const char *set_min_free_servers(cmd_parms *cmd, void *dummy, const char *arg)
{
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    ap_daemons_min_free = atoi(arg);
    if (ap_daemons_min_free <= 0) {
       ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, NULL, 
                    "WARNING: detected MinSpareServers set to non-positive.");
       ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, NULL, 
                    "Resetting to 1 to avoid almost certain Apache failure.");
       ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, NULL, 
                    "Please read the documentation.");
       ap_daemons_min_free = 1;
    }
       
    return NULL;
}

static const char *set_max_free_servers(cmd_parms *cmd, void *dummy, const char *arg)
{
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    ap_daemons_max_free = atoi(arg);
    return NULL;
}

static const char *set_max_clients (cmd_parms *cmd, void *dummy, const char *arg) 
{
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    ap_daemons_limit = atoi(arg);
    if (ap_daemons_limit > server_limit) {
       ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, NULL, 
                    "WARNING: MaxClients of %d exceeds ServerLimit value "
                    "of %d servers,", ap_daemons_limit, server_limit);
       ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, NULL, 
                    " lowering MaxClients to %d.  To increase, please "
                    "see the ServerLimit", server_limit);
       ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, NULL,
                    " directive.");
       ap_daemons_limit = server_limit;
    } 
    else if (ap_daemons_limit < 1) {
	ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, NULL, 
                     "WARNING: Require MaxClients > 0, setting to 1");
	ap_daemons_limit = 1;
    }
    return NULL;
}

static const char *set_server_limit (cmd_parms *cmd, void *dummy, const char *arg) 
{
    int tmp_server_limit;
    
    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);
    if (err != NULL) {
        return err;
    }

    tmp_server_limit = atoi(arg);
    /* you cannot change ServerLimit across a restart; ignore
     * any such attempts
     */
    if (first_server_limit &&
        tmp_server_limit != server_limit) {
        /* how do we log a message?  the error log is a bit bucket at this
         * point; we'll just have to set a flag so that ap_mpm_run()
         * logs a warning later
         */
        changed_limit_at_restart = 1;
        return NULL;
    }
    server_limit = tmp_server_limit;
    
    if (server_limit > MAX_SERVER_LIMIT) {
       ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, NULL, 
                    "WARNING: ServerLimit of %d exceeds compile time limit "
                    "of %d servers,", server_limit, MAX_SERVER_LIMIT);
       ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, NULL, 
                    " lowering ServerLimit to %d.", MAX_SERVER_LIMIT);
       server_limit = MAX_SERVER_LIMIT;
    } 
    else if (server_limit < 1) {
	ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, NULL, 
                     "WARNING: Require ServerLimit > 0, setting to 1");
	server_limit = 1;
    }
    return NULL;
}

static const command_rec prefork_cmds[] = {
UNIX_DAEMON_COMMANDS,
LISTEN_COMMANDS,
AP_INIT_TAKE1("StartServers", set_daemons_to_start, NULL, RSRC_CONF,
              "Number of child processes launched at server startup"),
AP_INIT_TAKE1("MinSpareServers", set_min_free_servers, NULL, RSRC_CONF,
              "Minimum number of idle children, to handle request spikes"),
AP_INIT_TAKE1("MaxSpareServers", set_max_free_servers, NULL, RSRC_CONF,
              "Maximum number of idle children"),
AP_INIT_TAKE1("MaxClients", set_max_clients, NULL, RSRC_CONF,
              "Maximum number of children alive at the same time"),
AP_INIT_TAKE1("ServerLimit", set_server_limit, NULL, RSRC_CONF,
              "Maximum value of MaxClients for this run of Apache"),
{ NULL }
};

module AP_MODULE_DECLARE_DATA mpm_prefork_module = {
    MPM20_MODULE_STUFF,
    ap_mpm_rewrite_args,        /* hook to run before apache parses args */
    NULL,			/* create per-directory config structure */
    NULL,			/* merge per-directory config structures */
    NULL,			/* create per-server config structure */
    NULL,			/* merge per-server config structures */
    prefork_cmds,		/* command apr_table_t */
    prefork_hooks,		/* register hooks */
};
