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<p class="MsoNormal"><span style="color:#1F497D">Update: I’ve realized that by setting peer.rcvbuf such that the setsockopt(s, SOL_SOCKET, SO_RCVBUF, ..) call in the beginning of ngx_event_connect_peer() is hit, my socket buffer size can be made larger, and
the effect of NGX_AGAIN being returned on the 2<sup>nd</sup> call isn’t really significant anymore, as an acceptable data transfer rate can now be achieved.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">But, just curious, if anyone can explain why NGX_AGAIN (and, internally, EGAIN from recv()) is being returned on the 2<sup>nd</sup> call, I’d love to know!
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> nginx-devel-bounces@nginx.org [mailto:nginx-devel-bounces@nginx.org]
<b>On Behalf Of </b>Abbot, Drew<br>
<b>Sent:</b> Thursday, August 15, 2013 5:25 PM<br>
<b>To:</b> nginx-devel@nginx.org<br>
<b>Subject:</b> help with issue related to ngx_peer_connection_t, and ngx_unix_recv() returning NGX_AGAIN<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Greetings nginx developers, <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I work at Acision, and we make use of nginx, especially its mail module, which we have added considerable code to. I'm currently experiencing issues related to non-blocking sockets and ngx_unix_recv() returning NGX_AGAIN which I can't
make sense of, and I was wondering if anyone could help. Forgive me if these questions are answered somewhere in this list, or elsewhere online -- if so, I cannot find them.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">So, my chief goal is to know the proper way to simply create a new ngx_connection_t (specifically, with non-blocking sockets and in the mail module), which gets properly scheduled via the "nginx event queue" -- that is, to create an ngx_connection_t
such that, when data arrives on the socket, the event engine calls my read handler, and when data is to be written, the event engine calls my write handler.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">To achieve that goal (to not only create an ngx_connection_t, but also have it "scheduled" in the "proper ngnix style"), I have thus far used ngx_event_connect_peer(), passing it the address of a local ngx_peer_connection_t variable, like
so:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> ngx_peer_connection_t peer;<o:p></o:p></p>
<p class="MsoNormal"> ngx_str_t peer_name = {13, (u_char*)"MyName"};<o:p></o:p></p>
<p class="MsoNormal"> ...<o:p></o:p></p>
<p class="MsoNormal"> /* build peer */<o:p></o:p></p>
<p class="MsoNormal"> peer.sockaddr = (struct sockaddr *) saddr; <o:p></o:p></p>
<p class="MsoNormal"> peer.socklen = sizeof(struct sockaddr_in);<o:p></o:p></p>
<p class="MsoNormal"> peer.name = &peer_name;<o:p></o:p></p>
<p class="MsoNormal"> peer.get = ngx_event_get_peer;<o:p></o:p></p>
<p class="MsoNormal"> peer.log = s->connection->log;<o:p></o:p></p>
<p class="MsoNormal"> peer.log_error = NGX_ERROR;<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> rc = ngx_event_connect_peer(&peer);<o:p></o:p></p>
<p class="MsoNormal"> if (rc == NGX_ERROR || rc == NGX_BUSY || rc == NGX_DECLINED)<o:p></o:p></p>
<p class="MsoNormal"> /* error */<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> peer.connection->data = MyData;<o:p></o:p></p>
<p class="MsoNormal"> peer.connection->pool = s->connection->pool;<o:p></o:p></p>
<p class="MsoNormal"> peer.connection->read->handler = my_read_handler;<o:p></o:p></p>
<p class="MsoNormal"> peer.connection->write->handler = my_write_handler;<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Using that approach, ngx_event_connect_peer() creates the ngx_connection_t as peer.connection, and by using ngx_post_event() on peer.connection->read and peer.connection->write, I've been able to force my handlers to hit, and also, the
appropriate handler (read or write) seems to be called when data is to be sent or received.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">That approach seemed ok at first, but I’ve been noticing strange behavior on the non-blocking sockets within my_read_handler(). In particular, I call ngx_unix_recv() in my_read_handler() to actually receive data, but in any given invocation
of my_read_handler(), the first call to ngx_unix_recv() never ends up reading more than 128 bytes, and the second call always returns NGX_AGAIN, as if no more data were available at that time. However, I know more data is available! For example, if I continue
to call ngx_unix_recv() is a loop, ngx_unix_recv() will return NGX_AGAIN forever, even though more data will definitely be available! It's not until a separate invocation my_read_handler() in the future occurs that ngx_unix_recv() doesn't return NGX_AGAIN,
but again, the first call returns at most 128 bytes and the second call returns NGX_AGAIN. And, this pattern continues. The result is that for very large transfers, the data transfer is very slow!<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Is there something I can do to avoid that behavior? What am I doing wrong? Do I really want to be using ngx_event_connect_peer() and an ngx_peer_connection_t to achieve my goal of creating a new nginx connection, which gets scheduled
via the event queue? <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks a bunch,<o:p></o:p></p>
<p class="MsoNormal">Drew Abbot, Acision<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif""><o:p> </o:p></span></p>
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