使用select

时间：2007-06-13 来源：transfan

Using select()
最近用Perl写的程序都是使用socket读写，并发访问时直接使用fork。这样做可以缩短响应时间，但耗费大量系统资源，需要有可靠手段对子进程进行管理，控制访问连接数量，提高每路进程的利用率。
select方法可在同一个进程中处理多个IO（每次取出加进去的IO集合里面已就绪的子集），在网上搜出下面一段代码，很好地演示了select的用法（针对IO::Select对象）。

... create socket as before ...
use IO::Select;
$read_set = new IO::Select(); # create handle set for reading

$read_set->add($s); # add the main socket to the set

while (1) { # forever

    # get a set of readable handles (blocks until at least one handle is ready)

    my ($rh_set) = IO::Select->select($read_set, undef, undef, 0);
    # take all readable handles in turn

    foreach $rh (@$rh_set) {
    # if it is the main socket then we have an incoming connection and

    # we should accept() it and then add the new socket to the $read_set

        if ($rh == $s) {
            $ns = $rh->accept();
            $read_set->add($ns);
        }
        # otherwise it is an ordinary socket and we should read and process the request

        else {
            $buf = <$rh>;
            if($buf) { # we get normal input

            # ... process $buf ...

            }
          else { # the client has closed the socket

                # remove the socket from the $read_set and close it

                $read_set->remove($rh);
                close($rh);
            }
        }
    }
}