linux - fork 和 waitpid 在 Linux 上失败。没有达到硬限制或软限制

Question

我有一个进程必须按需创建和关闭线程。

每个线程使用 open2 派生一个新进程。有时在长时间执行程序后，open2有时无法 fork 进程并给出“无法分配内存错误”，有时线程也会发生这种情况。我知道Linux有软硬限制但并发数我的服务器的线程和进程不超过这些值。

是否有类似进程和线程数量的计数器，可以在一段时间后消除线程和进程的创建？

如果是这样，像 Postgres 这样的服务器如何长期工作？该项目有多个使用 TCP 进行通信的进程，但导致我在 mplayer 前端描述的错误的部分是用 Perl 编写的。代码如下:

use strict;
use warnings;
use IO::Socket::INET;
use IO::Select;
use POSIX ":sys_wait_h";
use IPC::Open2;
use 5.010;
use Config;
BEGIN
{
    if(!$Config{useithreads})
    {
        die "Your perl does not compiled with threading support.";    
    }
}
use threads;
use threads::shared;
use constant
{
    SERVER_PORT=>5000,
    #Remote request packet fields
    PACKET_REQTYPE=>0,
    PACKET_FILENAM=>1,
    PACKET_VOLMLVL=>2,
    PACKET_ENDPOSI=>3,
    PACKET_SEEKPOS=>4,
    #our request typs
    PLAY_REQUEST=>1,
    STOP_REQUEST=>2,
    INFO_REQUEST=>3,
    VOCH_REQUEST=>4,
    PAUS_REQUEST=>5,
    PLPA_REQUEST=>6,
    SEEK_REQUEST=>7,
    #Play states
    STATE_PAUS=>0,
    STATE_PLAY=>1,
    STATE_STOP=>2,
};

#The following line must be added because of a bad behavior in the perl thread library that causes a SIGPIPE to be generated under heavy usage of the threads.
$SIG{PIPE} = 'IGNORE';
#This variable holds the server socket object
my $server_socket;
#This array is used to hold objects of our all threads
my @thread_objects;
#create the server socket
$server_socket=IO::Socket::INET->new(LocalPort=>SERVER_PORT,Listen=>20,Proto=>'tcp',Reuse=>1) or
die "Creating socket error ($@)";
#Now try to accept remote connections
print "Server socket created successfully now try to accept remote connections on port: ".SERVER_PORT."\n";
while(my $client_connection=$server_socket->accept())
{
    push @thread_objects,threads->create(\&player_thread,$client_connection);
    $thread_objects[$#thread_objects]->detach();
}



#This subroutine is used to play something using tcp-based commands
sub player_thread
{
    my $client_socket=shift;
    #create a new select object
    my $selector=IO::Select->new($client_socket);
    #this variabe is used to pars our request
    my @remote_request;
    #getting th thread id of the current thread
    my $tid=threads->self()->tid;
    #This variable is used to hold the pid of mplayer child
    my $mp_pid=-1;
    #Mplayer stdin and stdout file descriptors
    my ($MP_STDIN,$MP_STDOUT);
    #This variable is used to check if we are playing something now or not
    my $is_playing=STATE_STOP;


    print "Client thread $tid created.\n";
    while(1)
    {
        #check to see if we can read anything from our handler
        #print "Before select\n";
        #my @ready=$selector->can_read();
        #print "After select: @ready\n";
        #now the data is ready for reading so we read it here
        my $data=<$client_socket>;
        #This means if the connection is closed by the remote end
        if(!defined($data))
        {
            print "Remote connection has been closed in thread $tid mplayer id is: $mp_pid and state is: $is_playing.\n";
            #if we have an mplayer child when remote connection is closed we must wait for it
            #so that is work is done
            if($mp_pid!=-1 and $is_playing ==STATE_PLAY)
            {
                waitpid $mp_pid,0;
                $is_playing=STATE_STOP;
            }
            elsif($is_playing==STATE_PAUS and $mp_pid!=-1)
            {
                print "thread $tid is in the paused state, we must kill mplayer.\n";
                print $MP_STDIN "quit\n";
                waitpid $mp_pid,0;
                $is_playing=STATE_STOP;
            }
            last;
        }#if

        #FIXME:: Here we must validate our argument
        #Now we try to execute the command
        chomp($data);
        @remote_request=split ",",$data;
        print "@remote_request\n";

        #Trying to reap the death child and change the state of the thread
        my $dead_child=-1;
        $dead_child=&reaper($mp_pid);
        if($dead_child)
        {
            $is_playing=STATE_STOP;
            $mp_pid=-1;
        }

        given($remote_request[PACKET_REQTYPE])
        {
            when($_==PLAY_REQUEST)
            {
                print "Play request\n";
                if($is_playing==STATE_STOP)
                {
                    eval{$mp_pid=open2($MP_STDOUT,$MP_STDIN,"mplayer -slave -really-quiet -softvol -volume ".$remote_request[PACKET_VOLMLVL]." -endpos ".$remote_request[PACKET_ENDPOSI]." ./".$remote_request[PACKET_FILENAM]);};
                    print "Some error occurred in open2 system call: $@\n" if $@;
                    $is_playing=STATE_PLAY;
                    print "Mplayer pid: $mp_pid.\n";
                }
            }
            when($_==STOP_REQUEST)
            {
                print "Stop request\n";
                if($is_playing != STATE_STOP)
                {
                    print $MP_STDIN "pausing_keep stop\n";

                    #FIXME:: Maybe we should use WNOHANG here
                    my $id=waitpid $mp_pid,0;
                    print "Mplayer($id) stopped.\n";
                    $is_playing=STATE_STOP;
                    $mp_pid=-1;
                }
            }
            when($_==PAUS_REQUEST)
            {
                print "pause request\n";
                if($is_playing !=STATE_STOP)
                {
                    print $MP_STDIN "pausing_keep pause\n";
                    $is_playing=STATE_PAUS;
                }
            }
            when($_==VOCH_REQUEST)
            {
                print "volume change request\n";
                if($is_playing !=STATE_STOP)
                {
                    print $MP_STDIN "pausing_keep volume ".$remote_request[PACKET_VOLMLVL]." 1\n";
                }
            }
            when($_==INFO_REQUEST)
            {
                my $id;
                $id=&reaper($mp_pid);
                if($id > 0)
                {
                    print "Mplayer($id) stopped.\n";
                    $is_playing=STATE_STOP;
                    $mp_pid=-1;
                }

                given($is_playing)
                {
                    when($_==STATE_STOP)
                    {
                        print $client_socket "Stopped\n";
                    }
                    when($_==STATE_PAUS)
                    {
                        print $client_socket "Paused\n";
                    }
                    when($_==STATE_PLAY)
                    {
                        print $client_socket "Playing\n";
                    }
                }
            }
            when ($_==PLPA_REQUEST)
            {
                print "play paused request\n";
                if($is_playing==STATE_STOP)
                {
                    eval{$mp_pid=open2($MP_STDOUT,$MP_STDIN,"mplayer -slave -really-quiet -softvol -volume ".$remote_request[PACKET_VOLMLVL]." -endpos ".$remote_request[PACKET_ENDPOSI]." ./".$remote_request[PACKET_FILENAM]);};
                    print "Some error occurred in open2 system call: $@\n" if $@;
                    print $MP_STDIN "pausing_keep pause\n";
                    $is_playing=STATE_PAUS;
                }
            }
            when ($_==SEEK_REQUEST)
            {
                print "Seek request\n";
                if($is_playing != STATE_STOP)
                {
                    my $seek_pos=abs $remote_request[PACKET_SEEKPOS];
                    print $MP_STDIN "seek $seek_pos 2\n";
                    $is_playing=STATE_PLAY;
                }
            }
            default
            {
                warn "Invalid request($_)!!!";
                next;
            }
        }#Given

    }#while
    $client_socket->close();
    print "Thread $tid is exiting now, the child mplayer pid is: $mp_pid and state is: $is_playing.\n";
}
#The following subroutine takes a pid and if that pid is grater than 0 it tries to reap it
#if it is successful returns pid of the reaped process else 0
sub reaper
{
    my $pid=shift;
    if($pid > 0)
    {
        my $id=waitpid($pid,WNOHANG);
        if($id > 0)
        {
            return $id;               
        }
    }
    return 0;
}

Answer 1

"Can not allocate memory error" 是它所说的，要么是用户超出了它的内存配额(用 ulimit -m 检查，与 ps ux 比较) 或者你真的内存不足(free)。

最大用户进程的限制只是间接关联 - 如果您 fork() 更多进程然后用户的内存配额允许，fork() 将因 ENOMEM 而失败。

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