Limit the number of syscalls made by the Eventhandler.

runtime/bin/eventhandler_linux.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_LINUX)
 
 #include "bin/eventhandler.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 56 matching lines @@
 }
 
 
 // Register the file descriptor for a SocketData structure with epoll
 // if events are requested.
 static void UpdateEpollInstance(intptr_t epoll_fd_, SocketData* sd) {
   struct epoll_event event;
   event.events = sd->GetPollEvents();
   event.data.ptr = sd;
   if (sd->port() != 0 && event.events != 0) {
+    // Only report events once and wait for them to be re-enabled after the
+    // event has been handled by the Dart code.
+    event.events |= EPOLLONESHOT;
     int status = 0;
     if (sd->tracked_by_epoll()) {
       status = TEMP_FAILURE_RETRY(epoll_ctl(epoll_fd_,
                                             EPOLL_CTL_MOD,
                                             sd->fd(),
                                             &event));
     } else {
       status = TEMP_FAILURE_RETRY(epoll_ctl(epoll_fd_,
                                             EPOLL_CTL_ADD,
                                             sd->fd(),
@@ skipping 248 matching lines @@
 void EventHandlerImplementation::HandleEvents(struct epoll_event* events,
                                               int size) {
   bool interrupt_seen = false;
   for (int i = 0; i < size; i++) {
     if (events[i].data.ptr == NULL) {
       interrupt_seen = true;
     } else {
       SocketData* sd = reinterpret_cast<SocketData*>(events[i].data.ptr);
       intptr_t event_mask = GetPollEvents(events[i].events, sd);
       if (event_mask != 0) {
-        // Unregister events for the file descriptor. Events will be
-        // registered again when the current event has been handled in
-        // Dart code.
-        RemoveFromEpollInstance(epoll_fd_, sd);
         Dart_Port port = sd->port();
         ASSERT(port != 0);
         DartUtils::PostInt32(port, event_mask);
       }
     }
   }
   if (interrupt_seen) {
     // Handle after socket events, so we avoid closing a socket before we handle
     // the current events.
     HandleInterruptFd();
@@ skipping 36 matching lines @@
     if (millis > kMaxInt32) millis = kMaxInt32;
     intptr_t result = TEMP_FAILURE_RETRY(epoll_wait(handler_impl->epoll_fd_,
                                                     events,
                                                     kMaxEvents,
                                                     millis));
     ASSERT(EAGAIN == EWOULDBLOCK);
     if (result == -1) {
       if (errno != EWOULDBLOCK) {
         perror("Poll failed");
       }
+    } else if (result == 0) {
+      handler_impl->HandleTimeout();
     } else {
-      handler_impl->HandleTimeout();
       handler_impl->HandleEvents(events, result);
     }
   }
   delete handler;
 }
 
 
 void EventHandlerImplementation::Start(EventHandler* handler) {
   int result = dart::Thread::Start(&EventHandlerImplementation::Poll,
                                    reinterpret_cast<uword>(handler));
@@ skipping 23 matching lines @@
 
 uint32_t EventHandlerImplementation::GetHashmapHashFromFd(intptr_t fd) {
   // The hashmap does not support keys with value 0.
   return dart::Utils::WordHash(fd + 1);
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_LINUX)