Net::Server::PreFork

Section: User Contributed Perl Documentation (3)
Updated: 2021-01-27
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NAME

Net::Server::PreFork - Net::Server personality

SYNOPSIS

    use base qw(Net::Server::PreFork);

    sub process_request {
        #...code...
    }

    __PACKAGE__->run();

DESCRIPTION

Please read the pod on Net::Server and Net::Server::PreForkSimple first. This module is a personality, or extension, or sub class, of the Net::Server::PreForkSimple class which is a sub class of Net::Server. See Net::Server::PreForkSimple.

This personality binds to one or more ports and then forks "min_servers" child process. The server will make sure that at any given time there are "min_spare_servers" available to receive a client request, up to "max_servers". Each of these children will process up to "max_requests" client connections. This type is good for a heavily hit site, and should scale well for most applications. (Multi port accept is accomplished using flock to serialize the children).

At this time, it does not appear that this module will pass tests on Win32 systems. Any ideas or patches for making the tests pass would be welcome.

SAMPLE CODE

Please see the sample listed in Net::Server.

COMMAND LINE ARGUMENTS

In addition to the command line arguments of the Net::Server base class and the Net::Server::PreForkSimple parent class, Net::Server::PreFork contains several other configurable parameters. You really should also see Net::Server::PreForkSimple.

    Key                 Value                   Default
    min_servers         \d+                     5
    min_spare_servers   \d+                     2
    max_spare_servers   \d+                     10
    max_servers         \d+                     50
    max_requests        \d+                     1000

    serialize           (flock|semaphore
                         |pipe|none)            undef
    # serialize defaults to flock on multi_port or on Solaris
    lock_file           "filename"              File::Temp->new

    check_for_dead      \d+                     30
    check_for_waiting   \d+                     10

    max_dequeue         \d+                     undef
    check_for_dequeue   \d+                     undef

    child_communication 1                       undef

min_servers: The minimum number of servers to keep running.
min_spare_servers: The minimum number of servers to have waiting for requests. Minimum and maximum numbers should not be set to close to each other or the server will fork and kill children too often.
max_spare_servers: The maximum number of servers to have waiting for requests. See min_spare_servers.
max_servers: The maximum number of child servers to start. This does not apply to dequeue processes.
check_for_waiting: Seconds to wait before checking to see if we can kill off some waiting servers.
check_for_spawn: Seconds between checking to see if we need to spawn more children
min_child_ttl: Minimum number of seconds between starting children and killing a child process
child_communication: Enable child communication to parent via unix sockets. If set to true, will let children write to the socket contained in $self->{'server'}->{'parent_sock'}. The parent will be notified through child_is_talking_hook where the first argument is the socket to the child. The child's socket is stored in $self->{'server'}->{'children'}->{$child_pid}->{'sock'}.
serialize: See the documentation under Net::Server::PreForkSimple.

CONFIGURATION FILE

"Net::Server::PreFork" allows for the use of a configuration file to read in server parameters. The format of this conf file is simple key value pairs. Comments and white space are ignored.

    #-------------- file test.conf --------------

    ### server information
    min_servers   20
    max_servers   80
    min_spare_servers 10
    min_spare_servers 15

    max_requests  1000

    ### user and group to become
    user        somebody
    group       everybody

    ### logging ?
    log_file    /var/log/server.log
    log_level   3
    pid_file    /tmp/server.pid

    ### access control
    allow       .+\.(net|com)
    allow       domain\.com
    deny        a.+

    ### background the process?
    background  1

    ### ports to bind
    host        127.0.0.1
    port        localhost:20204
    port        20205

    ### reverse lookups ?
    # reverse_lookups on

    ### enable child communication ?
    # child_communication

    #-------------- file test.conf --------------

PROCESS FLOW

Process flow follows Net::Server until the loop phase. At this point "min_servers" are forked and wait for connections. When a child accepts a connection, finishs processing a client, or exits, it relays that information to the parent, which keeps track and makes sure there are enough children to fulfill "min_servers", "min_spare_servers", "max_spare_servers", and "max_servers".

HOOKS

The PreFork server has the following hooks in addition to the hooks provided by PreForkSimple. See Net::Server::PreForkSimple.

"$self->run_n_children_hook()": This hook occurs at the top of run_n_children which is called each time the server goes to start more child processes. This gives the parent to do a little of its own accountting (as desired). Idea for this hook came from James FitzGibbon.
"$self->parent_read_hook()": This hook occurs any time that the parent reads information from the child. The line from the child is sent as an argument.
"$self->child_is_talking_hook()": This hook occurs if child_communication is true and the child has written to $self->{'server'}->{'parent_sock'}. The first argument will be the open socket to the child.
"$self->idle_loop_hook()": This hook is called in every pass through the main process wait loop, every "check_for_waiting" seconds. The first argument is a reference to an array of file descriptors that can be read at the moment.
"$self->cleanup_dead_child_hook( $child )": This hook is called when a dead child is detected. A child is considered dead when the pid does no longer exist. This hook could be used to cleanup possible temporary files or locks left over by a dead child. =back

HOT DEPLOY

Since version 2.000, the PreFork server has accepted the TTIN and TTOU signals. When a TTIN is received, the min and max_servers are increased by 1. If a TTOU signal is received the min max_servers are decreased by 1. This allows for adjusting the number of handling processes without having to restart the server.

BUGS

Tests don't seem to work on Win32. Any ideas or patches would be welcome.

TO DO

See Net::Server

AUTHOR

Paul T. Seamons paul@seamons.com

THANKS