Wait for concurrent sweeper in vm/cc/PrintJSON.

runtime/vm/object_test.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"
 
 #include "vm/assembler.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
@@ skipping 4115 matching lines @@
     objects_->Add(&handle);
   }
  private:
   GrowableArray<Object*>* objects_;
 };
 
 
 TEST_CASE(PrintJSON) {
   Heap* heap = Isolate::Current()->heap();
   heap->CollectAllGarbage();
+  // We don't want to print garbage objects, so wait for concurrent sweeper.
+  // TODO(21620): Add heap iteration interface that excludes garbage (or
+  // use ObjectGraph).
+  PageSpace* old_space = heap->old_space();
+  {
+    MonitorLocker ml(old_space->tasks_lock());
+    while (old_space->tasks() > 0) {
+      ml.Wait();
+    }
+  }
   GrowableArray<Object*> objects;
   ObjectAccumulator acc(&objects);
   heap->IterateObjects(&acc);
   for (intptr_t i = 0; i < objects.length(); ++i) {
     JSONStream js;
     objects[i]->PrintJSON(&js, false);
     EXPECT_SUBSTRING("\"type\":", js.ToCString());
   }
 }
 
@@ skipping 322 matching lines @@
   EXPECT_VALID(h_result);
   Integer& result = Integer::Handle();
   result ^= Api::UnwrapHandle(h_result);
   String& foo = String::Handle(String::New("foo"));
   Integer& expected = Integer::Handle();
   expected ^= foo.HashCode();
   EXPECT(result.IsIdenticalTo(expected));
 }
 
 }  // namespace dart