Uses an open thread handle as the ThreadJoinId on Windows.

runtime/vm/os_thread_win.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"  // NOLINT
 #if defined(TARGET_OS_WINDOWS)
 
 #include "vm/growable_array.h"
 #include "vm/lockers.h"
 #include "vm/os_thread.h"
@@ skipping 73 matching lines @@
   }
 
   // Close the handle, so we don't leak the thread object.
   CloseHandle(reinterpret_cast<HANDLE>(thread));
 
   return 0;
 }
 
 
 const ThreadId OSThread::kInvalidThreadId = 0;
-const ThreadJoinId OSThread::kInvalidThreadJoinId = 0;
+const ThreadJoinId OSThread::kInvalidThreadJoinId = NULL;
 
 
 ThreadLocalKey OSThread::CreateThreadLocal(ThreadDestructor destructor) {
   ThreadLocalKey key = TlsAlloc();
   if (key == kUnsetThreadLocalKey) {
     FATAL1("TlsAlloc failed %d", GetLastError());
   }
   ThreadLocalData::AddThreadLocal(key, destructor);
   return key;
 }
@@ skipping 19 matching lines @@
   return ::GetCurrentThreadId();
 }
 
 
 ThreadId OSThread::GetCurrentThreadTraceId() {
   return ::GetCurrentThreadId();
 }
 
 
 ThreadJoinId OSThread::GetCurrentThreadJoinId() {
-  // TODO(zra): Use the thread handle as the join id in order to have a more
-  // reliable join on windows.
-  return ::GetCurrentThreadId();
+  HANDLE handle = OpenThread(SYNCHRONIZE, false, ::GetCurrentThreadId());
+  ASSERT(handle != NULL);
+  return handle;
 }
 
 
 void OSThread::Join(ThreadJoinId id) {
-  HANDLE handle = OpenThread(SYNCHRONIZE, false, id);
-
-  // TODO(zra): OSThread::Start() closes the handle to the thread. Thus, by the
-  // time we try to join the thread, its resources may have already been
-  // reclaimed, and joining will fail. This can be avoided in a couple of ways.
-  // First, GetCurrentThreadJoinId could call OpenThread and return a handle.
-  // This is bad, because each of those handles would have to be closed.
-  // Second OSThread could be refactored to no longer be AllStatic. Then the
-  // handle could be cached in the object by the Start method.
-  if (handle == NULL) {
-    return;
-  }
-
+  HANDLE handle = static_cast<HANDLE>(id);
+  ASSERT(handle != NULL);
   DWORD res = WaitForSingleObject(handle, INFINITE);
   CloseHandle(handle);
   ASSERT(res == WAIT_OBJECT_0);

[siva, 2016/05/16 17:59:27]

Are all thread guaranteed to call OSThread::Join() at some point? I only see
calls to Join from the thread pool threads, The main thread which is created by
the embedder and calls Dart_EnterIsolate will also end up with one of these
handles which never seems to be closed (leaks one handle per isolate).

[zra, 2016/05/16 20:32:54]

Changed to call GetCurrentThreadJoinId only for threads that will be joined.

 }
 
 
 intptr_t OSThread::ThreadIdToIntPtr(ThreadId id) {
   ASSERT(sizeof(id) <= sizeof(intptr_t));
   return static_cast<intptr_t>(id);
 }
 
 
 ThreadId OSThread::ThreadIdFromIntPtr(intptr_t id) {
@@ skipping 512 matching lines @@
 #pragma data_seg(".CRT$XLB")
 PIMAGE_TLS_CALLBACK p_thread_callback_dart = OnDartThreadExit;
 
 // Reset the default section.
 #pragma data_seg()
 
 #endif  // _WIN64
 }  // extern "C"
 
 #endif  // defined(TARGET_OS_WINDOWS)