Avoid allocating an exception object in the snapshot reader.

runtime/vm/snapshot.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/snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bigint_operations.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
@@ skipping 149 matching lines @@
       stream_(TokenStream::Handle(isolate)),
       data_(ExternalTypedData::Handle(isolate)),
       error_(UnhandledException::Handle(isolate)),
       backward_references_((kind == Snapshot::kFull) ?
                            kNumInitialReferencesInFullSnapshot :
                            kNumInitialReferences) {
 }
 
 
 RawObject* SnapshotReader::ReadObject() {
-  const Instance& null_object = Instance::Handle();
-  *ErrorHandle() = UnhandledException::New(null_object, null_object);
   // Setup for long jump in case there is an exception while reading.
   LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
     Object& obj = Object::Handle(ReadObjectImpl());
     for (intptr_t i = 0; i < backward_references_.length(); i++) {
       if (!backward_references_[i].is_deserialized()) {
         ReadObjectImpl();
         backward_references_[i].set_state(kIsDeserialized);
       }
     }
@@ skipping 535 matching lines @@
   ASSERT(isolate()->no_gc_scope_depth() != 0);
   ASSERT(Utils::IsAligned(size, kObjectAlignment));
   Heap* heap = isolate()->heap();
 
   uword address = heap->TryAllocate(size, Heap::kOld);
   if (address == 0) {
     // Use the preallocated out of memory exception to avoid calling
     // into dart code or allocating any code.
     // We do a longjmp at this point to unwind out of the entire
     // read part and return the error object back.
+    const Instance& null_object = Instance::Handle();
+    *ErrorHandle() = UnhandledException::New(null_object, null_object);

[siva, 2014/07/14 16:20:03]

TryAllocate just failed which means the heap is full, how will
UnhandledException::New(...) succeed?

Maybe we should preallocate the UnhandledException object just like how we
preallocate the out_of_memory exception object.

[Florian Schneider, 2014/07/14 17:02:40]

Good point. I'll try that instead.

     const Instance& exception =
         Instance::Handle(object_store()->out_of_memory());
     ErrorHandle()->set_exception(exception);
     Isolate::Current()->long_jump_base()->Jump(1, *ErrorHandle());
   }
 #if defined(DEBUG)
   // Zap the uninitialized memory area.
   uword current = address;
   uword end = address + size;
   while (current < end) {
@@ skipping 868 matching lines @@
     NoGCScope no_gc;
     WriteObject(obj.raw());
     UnmarkAll();
   } else {
     ThrowException(exception_type(), exception_msg());
   }
 }
 
 
 }  // namespace dart