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 Clécio
