Limit the number of syscalls made by the Eventhandler.

runtime/bin/eventhandler_macos.cc

Index: runtime/bin/eventhandler_macos.cc
diff --git a/runtime/bin/eventhandler_macos.cc b/runtime/bin/eventhandler_macos.cc
index 4fb47a8258a4aaa22527df93999aadcfbb3a1501..4b0566351be3a2a5faba11a09c1404a7a01c9baf 100644
--- a/runtime/bin/eventhandler_macos.cc
+++ b/runtime/bin/eventhandler_macos.cc
@@ -78,11 +78,19 @@ 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);
       }
@@ -94,7 +102,13 @@ static void UpdateKqueue(intptr_t kqueue_fd_, SocketData* sd) {
     // 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);
       }
@@ -342,12 +356,10 @@ void EventHandlerImplementation::HandleEvents(struct kevent* events,
       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);