perl中的套接字编程,perlio层的问题？

Question

我注意到perl中perlio层的一些问题.给我一个美好的一天来追踪它,并希望其他人知道这件事吗？最可怕的是,由于它的级别太低,我担心它会降低代码的可移植性.

服务器代码:

use strict;
use Socket;

socket(my $sock, AF_INET, SOCK_STREAM, getprotobyname('tcp')) or die();
setsockopt($sock, SOL_SOCKET, SO_REUSEADDR, 1) or die();
bind($sock, pack_sockaddr_in(23457, inet_aton('0.0.0.0'))) or die();
listen($sock, 10) or die();

my $paddr = accept(my $csock, $sock);
if (not $paddr) { 
    die();
}
my ($port, $iaddr) = unpack_sockaddr_in($paddr);
printf "accepted %s:%s\n", inet_ntoa($iaddr), $port;
send($csock, "1234567890", 0);
recv($csock, my $tmp, 8192, 0);
close($csock);
close($sock);

客户端代码(我稍微改变以测试):

use strict;
use Socket;
use PerlIO;

socket(my $sock, AF_INET, SOCK_STREAM, getprotobyname('tcp')) or die();
connect($sock, pack_sockaddr_in(23457, inet_aton('localhost'))) or die();
print "layers before = ".join(', ', PerlIO::get_layers($sock))."\n";
#binmode($sock, ':pop');  # uncomment this line to watch the code work...
print "layers after  = ".join(', ', PerlIO::get_layers($sock))."\n";

my $tmp;
print "1ret    = ".read($sock, $tmp, 1)."\n"; print "tmp $tmp\n"; stillpending($sock);
print "1ret    = ".read($sock, $tmp, 1)."\n"; print "tmp $tmp\n"; stillpending($sock);
print "1ret    = ".read($sock, $tmp, 1)."\n"; print "tmp $tmp\n"; stillpending($sock);
print "1ret    = ".read($sock, $tmp, 1)."\n"; print "tmp $tmp\n"; stillpending($sock);
print "8192ret = ".read($sock, $tmp, 8192)."\n"; print "tmp $tmp\n"; stillpending($sock);
send($sock, 'blah', 0);

close($sock);

服务器输出:

accepted 127.0.0.1:39944

注释了binmode的客户端输出(正在使用的perlio层):

layers before = unix, perlio
layers after  = unix, perlio
1ret    = 1
tmp 1
no more
1ret    = 1
tmp 2
no more
1ret    = 1
tmp 3
no more
1ret    = 1
tmp 4
no more

上面的块永远.

取消注释binmode的客户端输出(没有使用perlio层):

layers before = unix, perlio
layers after  = unix
1ret    = 1
tmp 1
still more
1ret    = 1
tmp 2
still more
1ret    = 1
tmp 3
still more
1ret    = 1
tmp 4
still more
8192ret = 6
tmp 567890
no more

我的问题是,select()当显然(通过strace)第一个read()调用消耗了服务器发送的整个输出(进入我想象的某个内部缓冲区)时,停止返回该数据.在read(..., 8192)没有perlio层的情况下,最后一个也将阻塞,它不会阻塞.

我想我有解决问题的方法(弹出perlio层),但我很好奇其他人的想法是什么？即使第一个perl读取(使用perlio层)已将所有内容读入内存,它是否select()报告no more数据未决的错误？

有没有其他人遇到过类似的问题？

Answer 1

这是预期的:如果你正在使用select(),你需要使用sysread()而不是read(),因为缓冲(你发现:).

来自perldoc -f select:

警告:除非POSIX允许,否则不应尝试将缓冲的I/O(如"read"或")与"select"混合使用,即使只是在POSIX系统上也是如此.你必须使用"sysread".