LWP :: UserAgent请求方法上的真实超时 [英] True timeout on LWP::UserAgent request method

问题描述

我正在尝试向不可靠的服务器实施请求.该请求很高兴，但我的Perl脚本成功完成并不需要100％.问题是服务器偶尔会死锁(我们试图找出原因)，并且请求将永远不会成功.由于服务器认为它是活动的，因此它保持套接字连接处于打开状态，因此LWP :: UserAgent的超时值对我们毫无用处.对请求强制绝对超时的最佳方法是什么?

I am trying to implement a request to an unreliable server. The request is a nice to have, but not 100% required for my perl script to successfully complete. The problem is that the server will occasionally deadlock (we're trying to figure out why) and the request will never succeed. Since the server thinks it is live, it keeps the socket connection open thus LWP::UserAgent's timeout value does us no good what-so-ever. What is the best way to enforce an absolute timeout on a request?

仅供参考，这不是DNS问题.僵局与同时访问我们的Postgres数据库的大量更新有关.为了进行测试，我们实质上在服务器响应处理程序中放置了while(1){}行.

FYI, this is not an DNS problem. The deadlock has something to do with a massive number of updates hitting our Postgres database at the same time. For testing purposes, we've essentially put a while(1) {} line in the servers response handler.

当前，代码如下:

my $ua = LWP::UserAgent->new;
ua->timeout(5); $ua->cookie_jar({});

my $req = HTTP::Request->new(POST => "http://$host:$port/auth/login");
$req->content_type('application/x-www-form-urlencoded');
$req->content("login[user]=$username&login[password]=$password");

# This line never returns 
$res = $ua->request($req);

我尝试使用信号触发超时，但这似乎不起作用.

I've tried using signals to trigger a timeout, but that does not seem to work.

eval {
    local $SIG{ALRM} = sub { die "alarm\n" };
    alarm(1);
    $res = $ua->request($req);
    alarm(0);
};
# This never runs
print "here\n";

我要使用的最终答案是由离线用户提出的，但我将在这里提及.由于某些原因，SigAction起作用，而$ SIG(ALRM)则不起作用.仍然不确定为什么，但这已经过测试.这是两个工作版本:

The final answer I'm going to use was proposed by someone offline, but I'll mention it here. For some reason, SigAction works while $SIG(ALRM) does not. Still not sure why, but this has been tested to work. Here are two working versions:

# Takes a LWP::UserAgent, and a HTTP::Request, returns a HTTP::Request
sub ua_request_with_timeout {
    my $ua = $_[0];
    my $req = $_[1];
    # Get whatever timeout is set for LWP and use that to 
    #  enforce a maximum timeout per request in case of server
    #  deadlock. (This has happened.)
    use Sys::SigAction qw( timeout_call );
    our $res = undef;
    if( timeout_call( 5, sub {$res = $ua->request($req);}) ) {
        return HTTP::Response->new( 408 ); #408 is the HTTP timeout
    } else {
        return $res;
    }
}
sub ua_request_with_timeout2 {
    print "ua_request_with_timeout\n";
    my $ua = $_[0];
    my $req = $_[1];
    # Get whatever timeout is set for LWP and use that to 
    #  enforce a maximum timeout per request in case of server
    #  deadlock. (This has happened.)
    my $timeout_for_client = $ua->timeout() - 2;
    our $socket_has_timedout = 0;

    use POSIX;
    sigaction SIGALRM, new POSIX::SigAction(
                                            sub {
                                                $socket_has_timedout = 1;
                                                die "alarm timeout";
                                            }
                                            ) or die "Error setting SIGALRM handler: $!\n";
    my $res = undef;
    eval {
        alarm ($timeout_for_client);
        $res = $ua->request($req);
        alarm(0);
    };
    if ( $socket_has_timedout ) {
        return HTTP::Response->new( 408 ); #408 is the HTTP timeout
    } else {
        return $res;
    }
}

推荐答案

您可以尝试

You might try LWPx::ParanoidAgent, a subclass of LWP::UserAgent which is more cautious about how it interacts with remote webservers.

除其他事项外，它还允许您指定全局超时.它是Brad Fitzpatrick作为LiveJournal项目的一部分开发的.

Among other things, it allows you to specify a global timeout. It was developed by Brad Fitzpatrick as part of the LiveJournal project.

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