Limit the number of syscalls made by the Eventhandler.

runtime/bin/eventhandler_macos.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_MACOS)
 
 #include "bin/eventhandler.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 60 matching lines @@
   }
 }
 
 
 // Update the kqueue registration for SocketData structure to reflect
 // the events currently of interest.
 static void UpdateKqueue(intptr_t kqueue_fd_, SocketData* sd) {
   static const intptr_t kMaxChanges = 2;
   intptr_t changes = 0;
   struct kevent events[kMaxChanges];
+  // Only report events once and wait for them to be re-enabled after the
+  // event has been handled by the Dart code. This is done by using EV_ONESHOT.
   if (sd->port() != 0) {
     // Register or unregister READ filter if needed.
     if (sd->HasReadEvent()) {
       if (!sd->read_tracked_by_kqueue()) {
-        EV_SET(events + changes, sd->fd(), EVFILT_READ, EV_ADD, 0, 0, sd);
+        EV_SET(events + changes,
+               sd->fd(),
+               EVFILT_READ,
+               EV_ADD | EV_ONESHOT,
+               0,
+               0,
+               sd);
         ++changes;
         sd->set_read_tracked_by_kqueue(true);
       }
     } else if (sd->read_tracked_by_kqueue()) {
       EV_SET(events + changes, sd->fd(), EVFILT_READ, EV_DELETE, 0, 0, NULL);
       ++changes;
       sd->set_read_tracked_by_kqueue(false);
     }
     // Register or unregister WRITE filter if needed.
     if (sd->HasWriteEvent()) {
       if (!sd->write_tracked_by_kqueue()) {
-        EV_SET(events + changes, sd->fd(), EVFILT_WRITE, EV_ADD, 0, 0, sd);
+        EV_SET(events + changes,
+               sd->fd(),
+               EVFILT_WRITE,
+               EV_ADD | EV_ONESHOT,
+               0,
+               0,
+               sd);
         ++changes;
         sd->set_write_tracked_by_kqueue(true);
       }
     } else if (sd->write_tracked_by_kqueue()) {
       EV_SET(events + changes, sd->fd(), EVFILT_WRITE, EV_DELETE, 0, 0, NULL);
       ++changes;
       sd->set_write_tracked_by_kqueue(false);
     }
   }
   if (changes > 0) {
@@ skipping 227 matching lines @@
     if ((events[i].flags & EV_ERROR) != 0) {
       const int kBufferSize = 1024;
       char error_message[kBufferSize];
       strerror_r(events[i].data, error_message, kBufferSize);
       FATAL1("kevent failed %s\n", error_message);
     }
     if (events[i].udata == NULL) {
       interrupt_seen = true;
     } else {
       SocketData* sd = reinterpret_cast<SocketData*>(events[i].udata);
+      sd->set_read_tracked_by_kqueue(false);
+      sd->set_write_tracked_by_kqueue(false);
       intptr_t event_mask = GetEvents(events + i, 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.
-        RemoveFromKqueue(kqueue_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 92 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_MACOS)