Thanks for agreeing. Added as src/examples/suspend_resume_epoll.c in 7d7ccbcd..8abd74f3.
Happy hacking!
Christian
On 03/13/2018 07:11 PM, Robert D Kocisko wrote:
> I agree with Silvio, it would be great to have this example included
> in the official examples.
>
> On Sun, Mar 11, 2018 at 2:11 PM, silvioprog <silviop...@gmail.com> wrote:
>> 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
>
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