Uses an open thread handle as the ThreadJoinId on Windows.

runtime/vm/os_thread.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 VM_OS_THREAD_H_
 #define VM_OS_THREAD_H_
 
 #include "platform/globals.h"
 #include "vm/allocation.h"
 #include "vm/globals.h"
@@ skipping 43 matching lines @@
   // this factory style method 'CreateOSThread' to create OSThread structures.
   // The method can return a NULL if the Dart VM is in shutdown mode.
   static OSThread* CreateOSThread();
   ~OSThread();
 
   ThreadId id() const {
     ASSERT(id_ != OSThread::kInvalidThreadId);
     return id_;
   }
 
-  ThreadJoinId join_id() const {
-    ASSERT(join_id_ != OSThread::kInvalidThreadJoinId);
-    return join_id_;
-  }
-
   ThreadId trace_id() const {
-    ASSERT(trace_id_ != OSThread::kInvalidThreadJoinId);
+    ASSERT(trace_id_ != OSThread::kInvalidThreadId);
     return trace_id_;
   }
 
   const char* name() const {
     return name_;
   }
 
   void SetName(const char* name);
 
   void set_name(const char* name) {
@@ skipping 86 matching lines @@
     return ThreadInlineImpl::GetThreadLocal(key);
   }
   static ThreadId GetCurrentThreadId();
   static void SetThreadLocal(ThreadLocalKey key, uword value);
   static intptr_t GetMaxStackSize();
   static void Join(ThreadJoinId id);
   static intptr_t ThreadIdToIntPtr(ThreadId id);
   static ThreadId ThreadIdFromIntPtr(intptr_t id);
   static bool Compare(ThreadId a, ThreadId b);
 
+  // This function can be called only once per OSThread, and should only be
+  // called when the retunred id will eventually be passed to OSThread::Join().
+  static ThreadJoinId GetCurrentThreadJoinId(OSThread* thread);
+
   // Called at VM startup and shutdown.
   static void InitOnce();
 
-  static bool IsThreadInList(ThreadJoinId join_id);
+  static bool IsThreadInList(ThreadId id);
 
   static void DisableOSThreadCreation();
   static void EnableOSThreadCreation();
 
   static const intptr_t kStackSizeBuffer = (4 * KB * kWordSize);
 
   static const ThreadId kInvalidThreadId;
   static const ThreadJoinId kInvalidThreadJoinId;
 
  private:
   // The constructor is private as CreateOSThread should be used
   // to create a new OSThread structure.
   OSThread();
 
   // These methods should not be used in a generic way and hence
   // are private, they have been added to solve the problem of
   // accessing the VM thread structure from an OSThread object
   // in the windows thread interrupter which is used for profiling.
   // We could eliminate this requirement if the windows thread interrupter
   // is implemented differently.
   Thread* thread() const { return thread_; }
   void set_thread(Thread* value) {
     thread_ = value;
   }
 
   static void Cleanup();
   static ThreadId GetCurrentThreadTraceId();
-  static ThreadJoinId GetCurrentThreadJoinId();
   static OSThread* GetOSThreadFromThread(Thread* thread);
   static void AddThreadToListLocked(OSThread* thread);
   static void RemoveThreadFromList(OSThread* thread);
   static OSThread* CreateAndSetUnknownThread();
 
   static ThreadLocalKey thread_key_;
 
   const ThreadId id_;
-  const ThreadJoinId join_id_;
+#if defined(DEBUG)
+  // In DEBUG mode we use this field to ensure that GetCurrentThreadJoinId is
+  // only called once per OSThread.
+  ThreadJoinId join_id_;
+#endif
   const ThreadId trace_id_;  // Used to interface with tracing tools.
   char* name_;  // A name for this thread.
 
   Mutex* timeline_block_lock_;
   TimelineEventBlock* timeline_block_;
 
   // All |Thread|s are registered in the thread list.
   OSThread* thread_list_next_;
 
   uintptr_t thread_interrupt_disabled_;
@@ skipping 116 matching lines @@
   friend class SafepointMonitorLocker;
   friend void Dart_TestMonitor();
   DISALLOW_COPY_AND_ASSIGN(Monitor);
 };
 
 
 }  // namespace dart
 
 
 #endif  // VM_OS_THREAD_H_