session_id赋值出现岂有此理的难题，

<br /><?php<br />/*<br /> * 生成验证码图片<br /> * author yuanjiang @2.16.2014<br />*/<br />define("IN_WD",true);<br />require('includes/init.php');<br /><br />$sessionid = session_id();<br /><br />$url = CLIENT_HOST.'createCaptcha.php';<br />$keyArr = array('sessionid'=>$sessionid);<br /><br />$captcha = $Common->file_post($url,$keyArr);<br />echo base64_encode($captcha);   //图片的base64编码，供客户端和web调用<br /><br />?><br />

<br /><?php<br />/*<br /> * 生成验证码图片<br /> * author yuanjiang @2.16.2014<br />*/<br />define("IN_WD",true);<br />$sessionid =  isset($_POST['sessionid']) ? $_POST['sessionid'] : '' ;     //根据post的sessionid切换session状态<br />if(!empty($sessionid))<br />{  <br />   session_id($sessionid);      //执行这一步的时候程序会卡死，当$sessionid不等于页面A.php的session_id时正确<br />}<br />session_start();<br />require('includes/cls_captcha.php');<br />$Captcha = new Captcha;<br />$Captcha->generate_image();     //生成图片<br />?><br />