master_avail.c

[詳解]

/*++
/* NAME
/*  master_avail 3
/* SUMMARY
/*  Postfix master - process creation policy
/* SYNOPSIS
/*  #include "master.h"
/*
/*  void    master_avail_listen(serv)
/*  MASTER_SERV *serv;
/*
/*  void    master_avail_cleanup(serv)
/*  MASTER_SERV *serv;
/*
/*  void    master_avail_more(serv, proc)
/*  MASTER_SERV *serv;
/*  MASTER_PROC *proc;
/*
/*  void    master_avail_less(serv, proc)
/*  MASTER_SERV *serv;
/*  MASTER_PROC *proc;
/* DESCRIPTION
/*  This module implements the process creation policy. As long as
/*  the allowed number of processes for the given service is not
/*  exceeded, a connection request is either handled by an existing
/*  available process, or this module causes a new process to be
/*  created to service the request.
/*
/*  When the service runs out of process slots, and the service
/*  is eligible for stress-mode operation, a warning is logged,
/*  servers are asked to restart at their convenience, and new
/*  servers are created with stress mode enabled.
/*
/*  master_avail_listen() ensures that someone monitors the service's
/*  listen socket for connection requests (as long as resources
/*  to handle connection requests are available).  This function may
/*  be called at random times, but it must be called after each status
/*  change of a service (throttled, process limit, etc.) or child
/*  process (taken, available, dead, etc.).
/*
/*  master_avail_cleanup() should be called when the named service
/*  is taken out of operation. It terminates child processes by
/*  sending SIGTERM.
/*
/*  master_avail_more() should be called when the named process
/*  has become available for servicing new connection requests.
/*  This function updates the process availability status and
/*  counter, and implicitly calls master_avail_listen().
/*
/*  master_avail_less() should be called when the named process
/*  has become unavailable for servicing new connection requests.
/*  This function updates the process availability status and
/*  counter, and implicitly calls master_avail_listen().
/* DIAGNOSTICS
/*  Panic: internal inconsistencies.
/* BUGS
/* SEE ALSO
/*  master_spawn(3), child process birth and death
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

/* System libraries. */

#include <sys_defs.h>

/* Utility library. */

#include <events.h>
#include <msg.h>

/* Application-specific. */

#include "master_proto.h"
#include "master.h"

/* master_avail_event - create child process to handle connection request */

static void master_avail_event(int event, void *context)
{
    MASTER_SERV *serv = (MASTER_SERV *) context;
    time_t  now;

    if (event == 0)             /* XXX Can this happen? */
    msg_panic("master_avail_event: null event");
    else {

    /*
     * When all servers for a public internet service are busy, we start
     * creating server processes with "-o stress=yes" on the command
     * line, and keep creating such processes until the process count is
     * below the limit for at least 1000 seconds. This provides a minimal
     * solution that can be adopted into legacy and stable Postfix
     * releases.
     * 
     * This is not the right place to update serv->stress_param_val in
     * response to stress level changes. Doing so would would contaminate
     * the "postfix reload" code with stress management implementation
     * details, creating a source of future bugs. Instead, we update
     * simple counters or flags here, and use their values to determine
     * the proper serv->stress_param_val value when exec-ing a server
     * process.
     */
    if (serv->stress_param_val != 0
        && !MASTER_LIMIT_OK(serv->max_proc, serv->total_proc + 1)) {
        now = event_time();
        if (serv->stress_expire_time < now)
        master_restart_service(serv, NO_CONF_RELOAD);
        serv->stress_expire_time = now + 1000;
    }
    master_spawn(serv);
    }
}

/* master_avail_listen - enforce the socket monitoring policy */

void    master_avail_listen(MASTER_SERV *serv)
{
    const char *myname = "master_avail_listen";
    int     listen_flag;
    time_t  now;
    int     n;

    /*
     * Caution: several other master_XXX modules call master_avail_listen(),
     * master_avail_more() or master_avail_less(). To avoid mutual dependency
     * problems, the code below invokes no code in other master_XXX modules,
     * and modifies no data that is maintained by other master_XXX modules.
     * 
     * When no-one else is monitoring the service's listen socket, start
     * monitoring the socket for connection requests. All this under the
     * restriction that we have sufficient resources to service a connection
     * request.
     */
    if (msg_verbose)
    msg_info("%s: %s avail %d total %d max %d", myname, serv->name,
         serv->avail_proc, serv->total_proc, serv->max_proc);
    if (MASTER_THROTTLED(serv) || serv->avail_proc > 0) {
    listen_flag = 0;
    } else if (MASTER_LIMIT_OK(serv->max_proc, serv->total_proc)) {
    listen_flag = 1;
    } else {
    listen_flag = 0;
    if (serv->stress_param_val != 0) {
        now = event_time();
        if (serv->busy_warn_time < now - 1000) {
        serv->busy_warn_time = now;
        msg_warn("service \"%s\" (%s) has reached its process limit \"%d\": "
             "new clients may experience noticeable delays",
             serv->ext_name, serv->name, serv->max_proc);
        msg_warn("to avoid this condition, increase the process count "
              "in master.cf or reduce the service time per client");
        msg_warn("see http://www.postfix.org/STRESS_README.html for "
              "examples of stress-adapting configuration settings");
        }
    }
    }
    if (listen_flag && !MASTER_LISTENING(serv)) {
    if (msg_verbose)
        msg_info("%s: enable events %s", myname, serv->name);
    for (n = 0; n < serv->listen_fd_count; n++)
        event_enable_read(serv->listen_fd[n], master_avail_event,
                  (void *) serv);
    serv->flags |= MASTER_FLAG_LISTEN;
    } else if (!listen_flag && MASTER_LISTENING(serv)) {
    if (msg_verbose)
        msg_info("%s: disable events %s", myname, serv->name);
    for (n = 0; n < serv->listen_fd_count; n++)
        event_disable_readwrite(serv->listen_fd[n]);
    serv->flags &= ~MASTER_FLAG_LISTEN;
    }
}

/* master_avail_cleanup - cleanup */

void    master_avail_cleanup(MASTER_SERV *serv)
{
    int     n;

    master_delete_children(serv);       /* XXX calls
                         * master_avail_listen */

    /*
     * This code is redundant because master_delete_children() throttles the
     * service temporarily before calling master_avail_listen/less(), which
     * then turn off read events. This temporary throttling is not documented
     * (it is only an optimization), and therefore we must not depend on it.
     */
    if (MASTER_LISTENING(serv)) {
    for (n = 0; n < serv->listen_fd_count; n++)
        event_disable_readwrite(serv->listen_fd[n]);
    serv->flags &= ~MASTER_FLAG_LISTEN;
    }
}

/* master_avail_more - one more available child process */

void    master_avail_more(MASTER_SERV *serv, MASTER_PROC *proc)
{
    const char *myname = "master_avail_more";

    /*
     * Caution: several other master_XXX modules call master_avail_listen(),
     * master_avail_more() or master_avail_less(). To avoid mutual dependency
     * problems, the code below invokes no code in other master_XXX modules,
     * and modifies no data that is maintained by other master_XXX modules.
     * 
     * This child process has become available for servicing connection
     * requests, so we can stop monitoring the service's listen socket. The
     * child will do it for us.
     */
    if (msg_verbose)
    msg_info("%s: pid %d (%s)", myname, proc->pid, proc->serv->name);
    if (proc->avail == MASTER_STAT_AVAIL)
    msg_panic("%s: process already available", myname);
    serv->avail_proc++;
    proc->avail = MASTER_STAT_AVAIL;
    master_avail_listen(serv);
}

/* master_avail_less - one less available child process */

void    master_avail_less(MASTER_SERV *serv, MASTER_PROC *proc)
{
    const char *myname = "master_avail_less";

    /*
     * Caution: several other master_XXX modules call master_avail_listen(),
     * master_avail_more() or master_avail_less(). To avoid mutual dependency
     * problems, the code below invokes no code in other master_XXX modules,
     * and modifies no data that is maintained by other master_XXX modules.
     * 
     * This child is no longer available for servicing connection requests. When
     * no child processes are available, start monitoring the service's
     * listen socket for new connection requests.
     */
    if (msg_verbose)
    msg_info("%s: pid %d (%s)", myname, proc->pid, proc->serv->name);
    if (proc->avail != MASTER_STAT_AVAIL)
    msg_panic("%s: process not available", myname);
    serv->avail_proc--;
    proc->avail = MASTER_STAT_TAKEN;
    master_avail_listen(serv);
}