Implement safepointing of threads

runtime/vm/bootstrap.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 "vm/bootstrap.h"
 
 #include "include/dart_api.h"
 
 #include "vm/bootstrap_natives.h"
 #include "vm/class_finalizer.h"
@@ skipping 191 matching lines @@
   const Error& error = Error::Handle(zone, Compile(lib, part_script));
   return Api::NewHandle(thread, error.raw());
 }
 
 
 static Dart_Handle BootstrapLibraryTagHandler(Dart_LibraryTag tag,
                                               Dart_Handle library,
                                               Dart_Handle uri) {
   Thread* thread = Thread::Current();
   Zone* zone = thread->zone();
+  // This handler calls into the VM directly and does not use the Dart
+  // API so we transition back to VM.
+  TransitionNativeToVM transition(thread);
   if (!Dart_IsLibrary(library)) {
     return Api::NewError("not a library");
   }
   if (!Dart_IsString(uri)) {
     return Api::NewError("uri is not a string");
   }
   if (tag == Dart_kCanonicalizeUrl) {
     // In the bootstrap loader we do not try and do any canonicalization.
     return uri;
   }
@@ skipping 125 matching lines @@
     Compiler::CompileClass(cls);
   }
 
   // Restore the library tag handler for the isolate.
   isolate->set_library_tag_handler(saved_tag_handler);
 
   return error.raw();
 }
 
 }  // namespace dart