Thread fixes for shutdown.

runtime/vm/thread_pool.cc

Index: runtime/vm/thread_pool.cc
diff --git a/runtime/vm/thread_pool.cc b/runtime/vm/thread_pool.cc
index 86d2f609db871a78995d25f75e8118c1e8c53a0b..4b1fb24a63504f4bbd1d94ce6c6e00a3a1968a3b 100644
--- a/runtime/vm/thread_pool.cc
+++ b/runtime/vm/thread_pool.cc
@@ -107,10 +107,18 @@ void ThreadPool::Shutdown() {
     while (current != NULL) {
       Worker* next = current->all_next_;
       ThreadId currentId = current->id();
-      if (currentId != id) {
+      if (currentId == OSThread::kInvalidThreadId) {
+        // If the thread id is invalid, it means the thread never started
+        // because OSThread creation was disabled. Destroy the Task and Worker.
+        delete current->task_;
+        delete current;
+        current = NULL;
+      } else if (currentId != id) {
         AddWorkerToShutdownList(current);
       }
-      current->Shutdown();
+      if (current != NULL) {
+        current->Shutdown();

[siva, 2015/12/30 20:51:02]

Why is it necessary to call current->Shutdown() when (currentId == id)?

[zra, 2015/12/30 22:36:28]

Thinking about this more, it is not safe for a thread-pool thread to call
ThreadPool::Shutdown(), so I've added an assert for that.

+      }
       current = next;
     }
     saved = NULL;