Implement safepointing of threads

runtime/vm/gc_sweeper.cc

 // Copyright (c) 2011, 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/gc_sweeper.h"
 
 #include "vm/freelist.h"
 #include "vm/globals.h"
 #include "vm/heap.h"
 #include "vm/lockers.h"
 #include "vm/pages.h"
+#include "vm/safepoint.h"
 #include "vm/thread_pool.h"
-#include "vm/thread_registry.h"
 
 namespace dart {
 
 bool GCSweeper::SweepPage(HeapPage* page, FreeList* freelist, bool locked) {
   // Keep track whether this page is still in use.
   bool in_use = false;
 
   bool is_executable = (page->type() == HeapPage::kExecutable);
   uword start = page->object_start();
   uword end = page->object_end();
@@ skipping 85 matching lines @@
     ASSERT(last_ != NULL);
     ASSERT(freelist_ != NULL);
     MonitorLocker ml(old_space_->tasks_lock());
     old_space_->set_tasks(old_space_->tasks() + 1);
     ml.Notify();
   }
 
   virtual void Run() {
     bool result = Thread::EnterIsolateAsHelper(task_isolate_);
     ASSERT(result);
+    Thread* thread = Thread::Current();
     GCSweeper sweeper;
 
     HeapPage* page = first_;
     HeapPage* prev_page = NULL;
 
     while (page != NULL) {
-      task_isolate_->thread_registry()->CheckSafepoint();
       HeapPage* next_page = page->next();
       ASSERT(page->type() == HeapPage::kData);
       bool page_in_use = sweeper.SweepPage(page, freelist_, false);
       if (page_in_use) {
         prev_page = page;
       } else {
         old_space_->FreePage(page, prev_page);
       }
       {
         // Notify the mutator thread that we have added elements to the free
         // list or that more capacity is available.
+        TransitionVMToBlocked transition(thread);

[zra, 2016/01/08 23:32:07]

I think I'm a little confused by the meaning of the Blocked state. We
potentially block every time we try to take a lock, or Wait on a monitor, but we
don't always put the thread into the Blocked state.

[siva, 2016/01/12 21:26:22]

True this was a hack I did initially to get things going and forgot to chenge.
Transition to Blocked state is used only when we go into WaitWithSafepointCheck

I have added thread->CheckForSafepoint which I use here to see if the thread
needs wait for a safepoint operation.

         MonitorLocker ml(old_space_->tasks_lock());
         ml.Notify();
       }
       if (page == last_) break;
       page = next_page;
     }
     // Exit isolate cleanly *before* notifying it, to avoid shutdown race.
     Thread::ExitIsolateAsHelper();
     // This sweeper task is done. Notify the original isolate.
     {
@@ skipping 19 matching lines @@
   SweeperTask* task =
       new SweeperTask(isolate,
                       isolate->heap()->old_space(),
                       first, last,
                       freelist);
   ThreadPool* pool = Dart::thread_pool();
   pool->Run(task);
 }
 
 }  // namespace dart