Hello dudes.

It would be nice to attach this example (or Christian's explanation) in
MHD's docs/examples. :-)

Thank you!

On Sun, Mar 11, 2018 at 2:11 PM, Christian Grothoff <groth...@gnunet.org>
wrote:

> Dear Bob,
>
> I've analyzed your code, and the issue is on your end: you simply didn't
> set the timeout correctly. When using an external event loop, it is
> mandatory that you ask MHD for the timeout using MHD_get_timeout() and
> use that with select/poll/epoll.  Then, you must call MHD_run() once
> whenever epoll() returns (including timeouts!).
>
> In your case, MHD would have given you a timeout of 0, but you used
> infinity instead, with predictable results...
>
> I've attached a corrected version of the code.
>
> Happy hacking!
>
> Christian
>
> On 03/02/2018 08:26 PM, Robert D Kocisko wrote:
> > First, thanks for your amazing work on MHD!
> >
> > This question is a near duplicate of the 2014 message thread from Tom
> > Cornell entitled "Trouble getting a response sent from a separate worker
> > thread (with external select)".  However, I am not using separate worker
> > threads--everything is in one thread and so I don't think the
> > recommendations found in that thread apply to my scenario.
> >
> > Basically after receiving a request from an HTTP client, I want to be
> > able to do some asynchronous 'work' which is really just waiting on
> > another process such as a database engine to calculate and return the
> > result which, when complete, I will forward back to the client.  This is
> > all done in one thread using epoll, so I don't want any blocking and I
> > don't want any busy loops.  MHD's external epoll support combined with
> > suspend/resume fits into this architecture perfectly, but there's a
> > problem: after resuming the connection and queueing the data, the
> > headers are sent to the client immediately, but the body of the response
> > does not get sent until another client request arrives.
> >
> > Anyway, to make this all concrete, I've put together a small working
> > example (below) which shows the problem.  This is built against the
> > latest dev rev (7f1dbb2) on elementaryOS (which is Ubuntu 16.04).  Every
> > time a request comes in it suspends the connection and starts a 1 second
> > timer which, when it expires, resumes the connection.  When the
> > connection is resumed the response is queued (simply echos the request
> > url).  I realize this example leaks timer fds and doesn't clean up
> > properly but it successfully demonstrates the problem.
> >
> > I have experimented with calling MHD_run() twice after
> > MHD_resume_connection() rather than the once required by the docs, and
> > that does seem to work, but that seems extremely hacky and I'm not sure
> > if twice is enough (why twice and not three times?).  I've skimmed the
> > source code looking for obvious answers but none are readily apparent to
> me.
> >
> > At this point I'm pretty sure that this is a bug with MHD but am I
> > missing something?
> >
> > Thanks!
> > Bob Kocisko
> >
> > -------------------------
> >
> > #include "platform.h"
> > #include <microhttpd.h>
> > #include <sys/epoll.h>
> > #include <sys/timerfd.h>
> >
> > #define TIMEOUT_INFINITE -1
> >
> > struct Request {
> >   struct MHD_Connection *connection;
> >   int timerfd;
> > };
> >
> > int epfd;
> > struct epoll_event evt;
> >
> > static int
> > ahc_echo (void *cls,
> >           struct MHD_Connection *connection,
> >           const char *url,
> >           const char *method,
> >           const char *version,
> >           const char *upload_data, size_t *upload_data_size, void **ptr)
> > {
> >   struct MHD_Response *response;
> >   int ret;
> >   struct Request* req;
> >   struct itimerspec ts;
> >   (void)url;               /* Unused. Silent compiler warning. */
> >   (void)version;           /* Unused. Silent compiler warning. */
> >   (void)upload_data;       /* Unused. Silent compiler warning. */
> >   (void)upload_data_size;  /* Unused. Silent compiler warning. */
> >
> >   req = *ptr;
> >   if (!req)
> >   {
> >
> >     req = malloc(sizeof(struct Request));
> >     req->connection = connection;
> >     req->timerfd = 0;
> >     *ptr = req;
> >     return MHD_YES;
> >   }
> >
> >   if (req->timerfd)
> >   {
> >     // send response (echo request url)
> >     response = MHD_create_response_from_buffer (strlen (url),
> >                                                 (void *) url,
> >                                                 MHD_RESPMEM_MUST_COPY);
> >     ret = MHD_queue_response (connection, MHD_HTTP_OK, response);
> >     MHD_destroy_response (response);
> >     return ret;
> >   }
> >   else
> >   {
> >     // create timer and suspend connection
> >     req->timerfd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK);
> >     if (-1 == req->timerfd)
> >     {
> >       printf("timerfd_create: %s", strerror(errno));
> >       return MHD_NO;
> >     }
> >     evt.events = EPOLLIN;
> >     evt.data.ptr = req;
> >     if (-1 == epoll_ctl(epfd, EPOLL_CTL_ADD, req->timerfd, &evt))
> >     {
> >       printf("epoll_ctl: %s", strerror(errno));
> >       return MHD_NO;
> >     }
> >     ts.it_value.tv_sec = 1;
> >     ts.it_value.tv_nsec = 0;
> >     ts.it_interval.tv_sec = 0;
> >     ts.it_interval.tv_nsec = 0;
> >     if (-1 == timerfd_settime(req->timerfd, 0, &ts, NULL))
> >     {
> >       printf("timerfd_settime: %s", strerror(errno));
> >       return MHD_NO;
> >     }
> >
> >     MHD_suspend_connection(connection);
> >     return MHD_YES;
> >   }
> > }
> >
> > static int
> > connection_done(struct MHD_Connection *connection,
> >                 void **con_cls,
> >                 enum MHD_RequestTerminationCode toe)
> > {
> >   free(*con_cls);
> > }
> >
> > int
> > main (int argc, char *const *argv)
> > {
> >   struct MHD_Daemon *d;
> >   const union MHD_DaemonInfo * info;
> >   int current_event_count;
> >   struct epoll_event events_list[1];
> >   struct Request *req;
> >   uint64_t timer_expirations;
> >
> >   if (argc != 2)
> >     {
> >       printf ("%s PORT\n", argv[0]);
> >       return 1;
> >     }
> >   d = MHD_start_daemon (MHD_USE_EPOLL | MHD_ALLOW_SUSPEND_RESUME,
> >                         atoi (argv[1]),
> >                         NULL, NULL, &ahc_echo, NULL,
> >                         MHD_OPTION_NOTIFY_COMPLETED, &connection_done,
> NULL,
> > MHD_OPTION_END);
> >   if (d == NULL)
> >     return 1;
> >
> >   info = MHD_get_daemon_info(d, MHD_DAEMON_INFO_EPOLL_FD);
> >   if (info == NULL)
> >     return 1;
> >
> >   epfd = epoll_create1(EPOLL_CLOEXEC);
> >   if (-1 == epfd)
> >     return 1;
> >
> >   evt.events = EPOLLIN;
> >   evt.data.ptr = NULL;
> >   if (-1 == epoll_ctl(epfd, EPOLL_CTL_ADD, info->epoll_fd, &evt))
> >     return 1;
> >
> >   while (1)
> >   {
> >     current_event_count = epoll_wait(epfd, events_list, 1,
> > TIMEOUT_INFINITE);
> >
> >     if (1 == current_event_count)
> >     {
> >       if (events_list[0].data.ptr)
> >       {
> >         // A timer has timed out
> >         req = events_list[0].data.ptr;
> >         // read from the fd so the system knows we heard the notice
> >         if (-1 == read(req->timerfd, &timer_expirations,
> > sizeof(timer_expirations)))
> >         {
> >           return 1;
> >         }
> >         // Now resume the connection
> >         MHD_resume_connection(req->connection);
> >         if (!MHD_run(d))
> >           return 1;
> >       }
> >       else
> >       {
> >         // MHD is ready
> >         if (!MHD_run(d))
> >           return 1;
> >       }
> >     }
> >     else if (0 == current_event_count)
> >     {
> >       // no events: continue
> >     }
> >     else
> >     {
> >       // error
> >       return 1;
> >     }
> >   }
> >
> >   return 0;
> > }
> >
> >
>



-- 
Silvio Cl├ęcio

Reply via email to