• <ins id="pjuwb"></ins>
    <blockquote id="pjuwb"><pre id="pjuwb"></pre></blockquote>
    <noscript id="pjuwb"></noscript>
          <sup id="pjuwb"><pre id="pjuwb"></pre></sup>
            <dd id="pjuwb"></dd>
            <abbr id="pjuwb"></abbr>

            大龍的博客

            常用鏈接

            統(tǒng)計

            最新評論

            gethostbyname timeout --- 轉(zhuǎn)

            總結(jié): 下面第一種方法經(jīng)過測試是可行的,第二種方法(多線程中使用)不能夠用信號中斷。

            so , 對信號的使用要非常小心。



            gethostbyname 是阻塞的, 非線程安全的,所以最好使用getaddrinfo , 它是線程安全的。

            要給gethostbyname 設(shè)置一個超時值, 用信號(alarm)實現(xiàn)是不行的(目前項目嵌入式平臺上面測試不行) 。


            下面是網(wǎng)上摘錄的解決該問題的方法, 對怎么繞過其他系統(tǒng)函數(shù)(無論是線程安全還是非安全的)也有很好的借鑒意義


            Hello,

            I need to add timeout to gethostbyname function in my program. I
            googled and searched archives, found some examples with alert(), but
            can't make it work :/ I would be grateful of someone could tell me how
            to do it.

            You can't. Or rather, you shouldn't.

            The trick with alarm(2) (not alert()), is to longjmp(3) from the signal
            handler to a context created with setjmp(3) before calling gethostbyname(3).
            This is, unfortunately, very common in Perl code (in Perl die() actually
            uses longjmp() internally to a context set from an eval statement).

            However, gethostbyname() keeps internal state, and afterward its unsafe
            to call the function again. gethostbyname_r() might be relatively safer,
            but you've probably also leaked a file descriptor and memory,
            meaning you could only do it so many times from a single process before it
            won't work anymore. (And from a strict C perspective, jumping from the
            signal handler itself is questionable.)

            You do have options.

            1) Multiple processes. Use child processes and the
            gethostbyname()+alarm() trick, and return the answer down a pipe to
            the parent. The child will just kill itself if it timeouts (or
            alternatively the parent will set the alarm and kill the child), since it
            cannot reliably do it's job afterward.

            2) Use threads in conjunction with gethostbyname_r(), or preferably
            getaddrinfo(3). Still, you cannot interrupt these functions within the
            thread, and so you have a few more decisions to make in terms of how you
            handle timeouts.

            3) Use a third-party asynchronous DNS library: ADNS, C-Ares and UDNS are
            the first ones which comes to mind, the former two probably being the most
            popular.

            posted on 2012-11-12 14:45 大龍 閱讀(3291) 評論(0)  編輯 收藏 引用


            只有注冊用戶登錄后才能發(fā)表評論。
            網(wǎng)站導(dǎo)航: 博客園   IT新聞   BlogJava   博問   Chat2DB   管理


            久久久久久久波多野结衣高潮| 久久久国产精品福利免费| 久久人人超碰精品CAOPOREN| 久久强奷乱码老熟女| 一本色道久久88精品综合| 精品亚洲综合久久中文字幕| 国产99久久久国产精品小说| 久久久久亚洲AV成人片| 青春久久| 国产精品99久久久久久宅男| 亚洲国产一成人久久精品| 久久久久国产一区二区 | 欧美久久综合性欧美| 思思久久99热只有频精品66| 久久精品国产福利国产秒| 亚洲天堂久久久| 久久国产香蕉视频| 中文字幕一区二区三区久久网站| 久久99精品国产麻豆宅宅| 欧美激情精品久久久久久| 久久综合久久久| 久久国产色AV免费观看| 亚洲综合精品香蕉久久网| 人人狠狠综合88综合久久| 精品水蜜桃久久久久久久| 伊人久久精品线影院| 国产精品99精品久久免费| 一本色道久久99一综合| 亚洲午夜久久久久妓女影院| 色妞色综合久久夜夜| 久久亚洲日韩看片无码| 少妇久久久久久被弄到高潮| 日本精品久久久久久久久免费| segui久久国产精品| 狠狠色综合久久久久尤物| 久久播电影网| 久久免费视频6| 久久天天躁狠狠躁夜夜躁2014| 久久精品中文字幕一区| 亚洲va久久久噜噜噜久久| AV无码久久久久不卡网站下载|