多进程读写问题

CODE:

#!/usr/bin/perl -w
use strict;
use POSIX;
use Fcntl ':flock';
use constant Max_fork =>6;
$SIG{CHLD}=sub {while((my $child=waitpid(-1,WNOHANG))>0) {}};
my $file=shift;
my $target_file=shift;
my @stat=stat($file);
$|++;
my $size=$stat[7];
my $average_process_blocks=sprintf("%d",($size/1024/Max_fork));
print "\$size = $size , \$average_process_blocks = $average_process_blocks\n";

my $read_fh;
my $write_target;
open($read_fh,"<$file");
open($write_target,">$target_file");
for(1..Max_fork)
{
    my $child = $_;
    my $pid=fork();
    if($pid==0){
        my $buff;
        my $offset = 1024 * ($child - 1) * $average_process_blocks;
#       my $ret1 = sysseek($read_fh, $offset, 0 );
#       my $ret2 = sysseek($write_target, $offset, 0);
        my $ret1=0; my $ret2 =0;
        for my $i (1..$average_process_blocks){
            sysseek($read_fh, $offset + 1024 *($i - 1), 0);
            sysread($read_fh,$buff,1024);

            sysseek($write_target, $offset + 1024 *($i - 1), 0);
            syswrite($write_target,$buff,1024);
        }
        my $ret3 = sysseek($write_target, 0, 1);
        close $read_fh;
        close $write_target;

        exit;
    }####else{wait}
}

for (1..6) {wait;}
my $buff;
my $last_block=$size-$average_process_blocks*Max_fork*1024;
sysseek($read_fh,$average_process_blocks*Max_fork*1024,0);
sysread($read_fh,$buff,$last_block);
sysseek($write_target,$average_process_blocks*Max_fork*1024,0);
syswrite($write_target,$buff,$last_block);
close ($read_fh);
close ($write_target);

QUOTE:

原帖由 027xiatian 于 2007-12-14 12:27 发表
恩,是的,
假如子进程读取没有重复,能保证,
一个子进程在写io的时候,syswrite是否是原子呢????

QUOTE:

原帖由 dajun 于 2007-12-14 13:50 发表
奇怪啊,为什么for循环里要不停的seek呢?

我本以为对于一个fh,只要seek一次就可以了,可是测试下来结果缺不是


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