https://svn.boost.org/trac10/ticket/7961 <p> RedHat5.8, kernel 2.6.32.26-17.el5, glibc 2.5-81.el5_8.7 The problem was detected with boost 1.49, but was confirmed with 1.53b1 also. </p> <p> Problem: handle_connect (connect completion handler) can be called before TCP open handshake completes. </p> <p> Unfortunately I could not strip my application to reasonable size, so I prefer not to post it. There is mail thread related to this bug at </p> <ul><li><a class="ext-link" href="http://sourceforge.net/mailarchive/forum.php?thread_name=kegjks%24c82%241%40ger.gmane.org&amp;forum_name=asio-users"><span class="icon">​</span>Asio Users Mail List</a> </li></ul><p> I believe there is a bug in epoll_reactor, the way it handles EPOLLHUP event on yet-not-connected sockets. Below I explain the details and symptoms. </p> <p> Here is strace output of such connects: </p> <pre class="wiki">[pid 25441] socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 9 [pid 25441] epoll_ctl(5, EPOLL_CTL_ADD, 9, {EPOLLIN|EPOLLPRI|EPOLLOUT|EPOLLERR|EPOLLHUP|EPOLLET, {u32=1811961744, u64=140515962017680}} &lt;unfinished ...&gt; [pid 25442] epoll_wait(5, &lt;unfinished ...&gt; [pid 25441] &lt;... epoll_ctl resumed&gt; ) = 0 [pid 25442] &lt;... epoll_wait resumed&gt; {{EPOLLOUT, {u32=1811958752, u64=140515962014688}}, {EPOLLIN, {u32=1811943784, u64=140515961999720}}, {EPOLLOUT|EPOLLHUP, {u32=1811961744, u64=140515962017680}}}, 128, 0) = 3 [pid 25441] ioctl(9, FIONBIO, [1]) = 0 [pid 25441] connect(9, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("xxx.xxx.193.11")}, 16) = -1 EINPROGRESS (Operation now in progress) *********** no epoll_wait after connect ********** [pid 25441] epoll_ctl(5, EPOLL_CTL_MOD, 9, {EPOLLIN|EPOLLPRI|EPOLLOUT|EPOLLERR|EPOLLHUP|EPOLLET, {u32=1811961744, u64=140515962017680}}) = 0 *********** calling handle_connect [pid 25442] getsockopt(9, SOL_SOCKET, SO_ERROR, [7782250667543887872], [4]) = 0 [pid 25442] getpeername(9, 0x40450360, [140514150055964]) = -1 ENOTCONN (Transport endpoint is not connected) [pid 25442] write(2, "connect error: ", 15connect error: ) = 15 [pid 25442] write(2, "Transport endpoint is not connec"..., 35Transport endpoint is not connected) = 35 [pid 25442] write(2, "\n", 1 ) = 1 </pre><p> As one can see, there is no epoll_wait after ::connect call, but connect handler was called. </p> <p> So, asio calls "::connect" and then immediately calls user handle_connect handler without calling (and waiting for) epoll_wait between ::connect and handle_connect. Thus handle_connect is called before the socket was actually connected. </p> <p> What may happen is: </p> <ol><li>main thread calls do_open and adds the socket to epoll queue. </li><li>service thread calls epoll_wait and it returns several events INCLUDING that socket. </li><li>main thread calls async_connect (and modifies the socket in epoll queue, but it does not matter at this point) </li><li>service thread processes the events it got form epoll_wait at step <a class="closed ticket" href="https://svn.boost.org/trac10/ticket/2" title="#2: Bugs: list::size should be const (closed: fixed)">#2</a> in a loop, and when it process that socket, the completion connect handler is called. </li></ol><p> The possible workaround is to ignore EPOLLHUP in epoll_reactor::descriptor_state::perform_io() until the socket got 'connected' state. </p> <p> I'm attaching the patch that works for me. It need to be carefully reviewed, because of possible unwanted side effects (e.g. lost socket disconnect error notifications). </p> en-us /htdocs/site/boost.png https://svn.boost.org/trac10/ticket/7961 Trac 1.4.3 Nikki Chumakov <nikkikom@…> Fri, 01 Feb 2013 16:05:22 GMT https://svn.boost.org/trac10/ticket/7961 https://svn.boost.org/trac10/ticket/7961 <ul> <li><strong>attachment</strong> → <span class="trac-field-new">boost-1.53.0b1-asio-epoll-reactor.patch</span> </li> </ul> <p> Suggested patch for boost-1.53b1 </p> Ticket anonymous Mon, 04 Mar 2013 01:53:13 GMT https://svn.boost.org/trac10/ticket/7961#comment:3 https://svn.boost.org/trac10/ticket/7961#comment:3 <ul> <li><strong>status</strong> <span class="trac-field-old">new</span> → <span class="trac-field-new">closed</span> </li> <li><strong>resolution</strong> → <span class="trac-field-new">fixed</span> </li> </ul> Ticket