Fix race and limit access to mutator_thread_.

runtime/vm/thread.cc

 // Copyright (c) 2015, 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 "vm/thread.h"
 
 #include "vm/growable_array.h"
 #include "vm/isolate.h"
 #include "vm/lockers.h"
 #include "vm/object.h"
@@ skipping 105 matching lines @@
   ASSERT(reg->Contains(this));
   reg->SaveStateFrom(this, state_);
   ClearState();
 }
 
 
 void Thread::EnterIsolate(Isolate* isolate) {
   Thread* thread = Thread::Current();
   ASSERT(thread != NULL);
   ASSERT(thread->isolate() == NULL);
-  ASSERT(isolate->mutator_thread() == NULL);
+  ASSERT(!isolate->HasMutatorThread());
   thread->isolate_ = isolate;
-  isolate->set_mutator_thread(thread);
+  isolate->MakeCurrentThreadMutator(thread);
   // TODO(koda): Migrate thread_state_ and profile_data_ to Thread, to allow
   // helper threads concurrent with mutator.
   ASSERT(isolate->thread_state() == NULL);
   InterruptableThreadState* thread_state =
       ThreadInterrupter::GetCurrentThreadState();
 #if defined(DEBUG)
   Isolate::CheckForDuplicateThreadState(thread_state);
 #endif
   ASSERT(thread_state != NULL);
   Profiler::BeginExecution(isolate);
@@ skipping 16 matching lines @@
   StoreBufferBlock* block = thread->store_buffer_block_;
   thread->store_buffer_block_ = NULL;
   isolate->store_buffer()->PushBlock(block);
   if (isolate->is_runnable()) {
     isolate->set_vm_tag(VMTag::kIdleTagId);
   } else {
     isolate->set_vm_tag(VMTag::kLoadWaitTagId);
   }
   isolate->set_thread_state(NULL);
   Profiler::EndExecution(isolate);
-  isolate->set_mutator_thread(NULL);
+  isolate->ClearMutatorThread();
   thread->isolate_ = NULL;
   ASSERT(Isolate::Current() == NULL);
   thread->heap_ = NULL;
 }
 
 
 void Thread::EnterIsolateAsHelper(Isolate* isolate) {
   Thread* thread = Thread::Current();
   ASSERT(thread != NULL);
   ASSERT(thread->isolate() == NULL);
   thread->isolate_ = isolate;
   ASSERT(isolate->heap() != NULL);
   thread->heap_ = isolate->heap();
   // Do not update isolate->mutator_thread, but perform sanity check:
   // this thread should not be both the main mutator and helper.
-  ASSERT(isolate->mutator_thread() != thread);
+  ASSERT(!isolate->MutatorThreadIsCurrentThread());
   thread->Schedule(isolate);
 }
 
 
 void Thread::ExitIsolateAsHelper() {
   Thread* thread = Thread::Current();
   // If the helper thread chose to use the store buffer, check that it has
   // already been flushed manually.
   ASSERT(thread->store_buffer_block_ == NULL);
   Isolate* isolate = thread->isolate();
   ASSERT(isolate != NULL);
   thread->Unschedule();
   thread->isolate_ = NULL;
   thread->heap_ = NULL;
-  ASSERT(isolate->mutator_thread() != thread);
+  ASSERT(!isolate->MutatorThreadIsCurrentThread());
 }
 
 
 void Thread::PrepareForGC() {
   Thread* thread = Thread::Current();
   StoreBuffer* sb = thread->isolate()->store_buffer();
   StoreBufferBlock* block = thread->store_buffer_block_;
   thread->store_buffer_block_ = NULL;
   const bool kCheckThreshold = false;  // Prevent scheduling another GC.
   sb->PushBlock(block, kCheckThreshold);
@@ skipping 51 matching lines @@
 #define COMPUTE_OFFSET(type_name, member_name, expr, default_init_value)       \
   ASSERT((expr)->IsVMHeapObject());                                            \
   if (object.raw() == expr) return Thread::member_name##offset();
 CACHED_VM_OBJECTS_LIST(COMPUTE_OFFSET)
 #undef COMPUTE_OFFSET
   UNREACHABLE();
   return -1;
 }
 
 }  // namespace dart