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copied!<p>Below is a simple <code>libevent</code> toy program that synthesizes <code>EINPROGRESS</code>, and then waits for the connection to complete by waiting for <code>EV_WRITE</code>. Basically, this program shows that in your application, you should attempt to do the <code>connect</code> call first, and if it fails with <code>EINPROGRESS</code>, you should wait for completion before performing I/O.</p> <p>This is the <code>libevent</code> callback function:</p> <pre><code>extern "C" void on_connect (int sock, short ev, void *arg) { assert(ev == EV_WRITE); std::cout << "got wrieable on: " << sock << '\n'; int optval = -1; socklen_t optlen = sizeof(optval); getsockopt(sock, SOL_SOCKET, SO_ERROR, &optval, &optlen); assert(optval == 0); std::cout << "succesful asynchronous connect on: " << sock << '\n'; event_loopbreak(); } </code></pre> <p>These are some helper functions used by the toy application:</p> <pre><code>static void init_addr (struct sockaddr_in *addr, short port) { memset(addr, '\0', sizeof(*addr)); addr->sin_family = AF_INET; addr->sin_port = htons(port); addr->sin_addr.s_addr = htonl(INADDR_LOOPBACK); } static void setup_accept (int sock) { const int one = 1; struct sockaddr_in addr; init_addr(&addr, 9876); setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)); bind(sock, (struct sockaddr *)&addr, sizeof(addr)); listen(sock, 1); } static int complete_accept (int sock) { struct sockaddr_in addr; socklen_t addrlen = sizeof(addr); return accept(sock, (struct sockaddr *)&addr, &addrlen); } static int try_connect (int sock) { struct sockaddr_in addr; init_addr(&addr, 9876); return connect(sock, (struct sockaddr *)&addr, sizeof(addr)); } </code></pre> <p>And the <code>main</code> program is below:</p> <pre><code>int main () { int accept_sock = socket(PF_INET, SOCK_STREAM, 0); setup_accept(accept_sock); int sock = socket(PF_INET, SOCK_STREAM, 0); fcntl(sock, F_SETFL, fcntl(sock, F_GETFL) | O_NONBLOCK); std::cout << "trying first connect on: " << sock << '\n'; int r = try_connect(sock); assert(r < 0 && errno == EINPROGRESS); event_init(); struct event ev_connect; event_set(&ev_connect, sock, EV_WRITE, on_connect, 0); event_add(&ev_connect, 0); int new_sock = complete_accept(accept_sock); event_dispatch(); return 0; } </code></pre>

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