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[libmicrohttpd] MHD_suspend_connection and MHD_resume_connection with MH

From: Denis Dowling
Subject: [libmicrohttpd] MHD_suspend_connection and MHD_resume_connection with MHD_USE_POLL
Date: Thu, 9 Apr 2015 05:28:51 +0000

Hi all,


I was trying to use MHD_suspend_connection() and MHD_resume_connection() to implement long polling on a request. I am using options MHD_USE_SELECT_INTERNALLY and MHD_USE_POLL options. I noticed the server thread went to 100% CPU after the first MHD_resume_connection() call. Looking at the code in MHD_poll_all() I can see that the file descriptor from daemon->wpipe[0] gets inserted into the list of file descriptors to poll but this file descriptor is never read so every time this function is called it returns immediately. The code works fine if I drop to using just MHD_USE_SELECT_INTERNALLY.


The patch below fixes the problem.





Index: src/microhttpd/daemon.c


--- src/microhttpd/daemon.c     (revision 35509)

+++ src/microhttpd/daemon.c  (working copy)

@@ -2317,6 +2317,8 @@

     int timeout;

     unsigned int poll_server;

     int poll_listen;

+    int poll_pipe;

+    char tmp;

     memset (p, 0, sizeof (p));

     poll_server = 0;

@@ -2331,11 +2333,13 @@

               poll_listen = (int) poll_server;



+    poll_pipe = -1;

     if (MHD_INVALID_PIPE_ != daemon->wpipe[0])


               p[poll_server].fd = daemon->wpipe[0];

               p[poll_server].events = POLLIN;

               p[poll_server].revents = 0;

+        poll_pipe = (int) poll_server;



     if (may_block == MHD_NO)

@@ -2433,6 +2437,11 @@

     if ( (-1 != poll_listen) &&

                (0 != (p[poll_listen].revents & POLLIN)) )

       (void) MHD_accept_connection (daemon);


+    /* handle pipe FD */

+    if ( (-1 != poll_pipe) &&

+             (0 != (p[poll_pipe].revents & POLLIN)) )

+      (void) MHD_pipe_read_ (daemon->wpipe[0], &tmp, sizeof (tmp));


   return MHD_YES;


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