Make the event-handler handle backpreasure.

runtime/bin/eventhandler_macos.h

 // 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.
 
 #ifndef BIN_EVENTHANDLER_MACOS_H_
 #define BIN_EVENTHANDLER_MACOS_H_
 
 #if !defined(BIN_EVENTHANDLER_H_)
 #error Do not include eventhandler_macos.h directly; use eventhandler.h instead.
 #endif
 
 #include <unistd.h>
-#include <errno.h>
 #include <sys/event.h>  // NOLINT
 #include <sys/socket.h>
 
 #include "platform/hashmap.h"
 
 
 namespace dart {
 namespace bin {
 
 class InterruptMessage {
  public:
   intptr_t id;
   Dart_Port dart_port;
   int64_t data;
 };
 
 
 class SocketData {
  public:
   explicit SocketData(intptr_t fd)
       : fd_(fd),
         port_(0),
         mask_(0),
-        tracked_by_kqueue_(false) {
+        tracked_by_kqueue_(false),
+        tokens_(8) {
     ASSERT(fd_ != -1);
   }
 
   bool HasReadEvent();
   bool HasWriteEvent();
 
-  void ShutdownRead() {
-    shutdown(fd_, SHUT_RD);
-  }
-
-  void ShutdownWrite() {
-    shutdown(fd_, SHUT_WR);
-  }
-
   void Close() {
     port_ = 0;
     mask_ = 0;
     close(fd_);
     fd_ = -1;
   }
 
   bool IsListeningSocket() { return (mask_ & (1 << kListeningSocket)) != 0; }
-  bool IsPipe() { return (mask_ & (1 << kPipe)) != 0; }
 
   void SetPortAndMask(Dart_Port port, intptr_t mask) {
     ASSERT(fd_ != -1);
     port_ = port;
     mask_ = mask;
   }
 
   intptr_t fd() { return fd_; }
   Dart_Port port() { return port_; }
   intptr_t mask() { return mask_; }
   bool tracked_by_kqueue() { return tracked_by_kqueue_; }
   void set_tracked_by_kqueue(bool value) {
     tracked_by_kqueue_ = value;
   }
 
+  // Returns true if the last token was taken.
+  bool TakeToken() {
+    tokens_--;
+    return tokens_ == 0;
+  }
+
+  // Returns true if the tokens was 0 before adding.
+  bool ReturnToken() {
+    tokens_++;
+    return tokens_ == 1;
+  }
+
  private:
   intptr_t fd_;
   Dart_Port port_;
   intptr_t mask_;
   bool tracked_by_kqueue_;
+  int tokens_;
 };
 
 
 class EventHandlerImplementation {
  public:
   EventHandlerImplementation();
   ~EventHandlerImplementation();
 
   // Gets the socket data structure for a given file
   // descriptor. Creates a new one if one is not found.
-  SocketData* GetSocketData(intptr_t fd, bool* is_new);
-  void Notify(intptr_t id, Dart_Port dart_port, int64_t data);
+  SocketData* GetSocketData(intptr_t fd);
+  void SendData(intptr_t id, Dart_Port dart_port, int64_t data);
   void Start(EventHandler* handler);
   void Shutdown();
 
  private:
   int64_t GetTimeout();
   void HandleEvents(struct kevent* events, int size);
   void HandleTimeout();
   static void EventHandlerEntry(uword args);
   void WakeupHandler(intptr_t id, Dart_Port dart_port, int64_t data);
   void HandleInterruptFd();
   void SetPort(intptr_t fd, Dart_Port dart_port, intptr_t mask);
   intptr_t GetEvents(struct kevent* event, SocketData* sd);
   static void* GetHashmapKeyFromFd(intptr_t fd);
   static uint32_t GetHashmapHashFromFd(intptr_t fd);
 
   HashMap socket_map_;
   TimeoutQueue timeout_queue_;
   bool shutdown_;
   int interrupt_fds_[2];
   int kqueue_fd_;
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_EVENTHANDLER_MACOS_H_