[libmicrohttpd2] 12/12: get_all_net_updates_by_epoll(): reduced the size of the data passed to the kernel

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karlson2k pushed a commit to branch master
in repository libmicrohttpd2.

commit cdd4c1f9cc9686fc57ce9e5894c77fb70b3529c6
Author: Evgeny Grin (Karlson2k) <k2k@drgrin.dev>
AuthorDate: Fri Jun 6 15:59:25 2025 +0200

    get_all_net_updates_by_epoll(): reduced the size of the data passed to the 
kernel
    
    Fixed possible wait for the second batch of epoll data
---
 src/mhd2/events_process.c | 31 ++++++++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/src/mhd2/events_process.c b/src/mhd2/events_process.c
index 6008c0e..1f67a00 100644
--- a/src/mhd2/events_process.c
+++ b/src/mhd2/events_process.c
@@ -1578,6 +1578,7 @@ update_statuses_from_eevents (struct MHD_Daemon *restrict 
d,
 static MHD_FN_PAR_NONNULL_ (1) bool
 get_all_net_updates_by_epoll (struct MHD_Daemon *restrict d)
 {
+  int max_events;
   int num_events;
   unsigned int events_processed;
   int max_wait;
@@ -1591,6 +1592,21 @@ get_all_net_updates_by_epoll (struct MHD_Daemon 
*restrict d)
 
   // TODO: add listen socket enable/disable
 
+  /* Minimise amount of data passed from userspace to kernel and back */
+  max_events = d->conns.cfg.count_limit;
+#ifdef MHD_SUPPORT_THREADS
+  ++max_events;
+#endif /* MHD_SUPPORT_THREADS */
+  if (MHD_INVALID_SOCKET != d->net.listen.fd)
+    ++max_events;
+  /* Make sure that one extra slot used to clearly detect that all events
+   * were gotten. */
+  ++max_events;
+  if (0 > max_events)
+    max_events = (int) (((unsigned int)~((unsigned int) 0)) >> 1);
+  if (max_events > (int) d->events.data.epoll.num_elements)
+    max_events = (int) d->events.data.epoll.num_elements;
+
   events_processed = 0;
   max_wait = get_max_wait (d); // TODO: use correct timeout value
   do
@@ -1604,13 +1620,13 @@ get_all_net_updates_by_epoll (struct MHD_Daemon 
*restrict d)
 #endif /* mhd_DEBUG_POLLING_FDS */
     num_events = epoll_wait (d->events.data.epoll.e_fd,
                              d->events.data.epoll.events,
-                             (int) d->events.data.epoll.num_elements,
+                             max_events,
                              max_wait);
 #ifdef mhd_DEBUG_POLLING_FDS
     fprintf (stderr,
              "### (Finished) epoll_wait(%d, events, %d, %d) -> %d\n",
              d->events.data.epoll.e_fd,
-             (int) d->events.data.epoll.num_elements,
+             max_events,
              max_wait,
              num_events);
 #endif /* mhd_DEBUG_POLLING_FDS */
@@ -1628,11 +1644,16 @@ get_all_net_updates_by_epoll (struct MHD_Daemon 
*restrict d)
     }
     if (! update_statuses_from_eevents (d, (unsigned int) num_events))
       return false;
+    if (max_events > num_events)
+      return true; /* All events have been read */
+
+    /* Use all buffer for the next getting events round(s) */
+    max_events = d->events.data.epoll.num_elements;
+    max_wait = 0; /* Do not block on the next getting events rounds */
 
     events_processed += (unsigned int) num_events; /* Avoid reading too many 
events */
-  } while ((((unsigned int) num_events) == d->events.data.epoll.num_elements) 
&&
-           ((events_processed < d->conns.cfg.count_limit)
-            || (events_processed < d->conns.cfg.count_limit + 2)));
+  } while ((events_processed < d->conns.cfg.count_limit)
+            || (events_processed < d->conns.cfg.count_limit + 2));
 
   return true;
 }

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