Zero-sized new-space for VM isolate.

runtime/vm/scavenger.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/scavenger.h"
 
 #include <algorithm>
 #include <map>
 #include <utility>
 
@@ skipping 299 matching lines @@
     : heap_(heap),
       object_alignment_(object_alignment),
       scavenging_(false),
       gc_time_micros_(0),
       collections_(0),
       external_size_(0) {
   // Verify assumptions about the first word in objects which the scavenger is
   // going to use for forwarding pointers.
   ASSERT(Object::tags_offset() == 0);
 
-  // Allocate the virtual memory for this scavenge heap.
-  space_ = VirtualMemory::Reserve(max_capacity_in_words << kWordSizeLog2);
-  if (space_ == NULL) {
-    FATAL("Out of memory.\n");
+  if (max_capacity_in_words == 0) {
+    space_ = NULL;
+    to_ = new MemoryRegion(NULL, 0);
+    from_ = new MemoryRegion(NULL, 0);
+  } else {
+    // Allocate the virtual memory for this scavenge heap.
+    space_ = VirtualMemory::Reserve(max_capacity_in_words << kWordSizeLog2);
+    if (space_ == NULL) {
+      FATAL("Out of memory.\n");
+    }
+
+    // Allocate the entire space at the beginning.
+    space_->Commit(false);
+
+    // Setup the semi spaces.
+    uword semi_space_size = space_->size() / 2;
+    ASSERT((semi_space_size & (VirtualMemory::PageSize() - 1)) == 0);
+    to_ = new MemoryRegion(space_->address(), semi_space_size);
+    uword middle = space_->start() + semi_space_size;
+    from_ = new MemoryRegion(reinterpret_cast<void*>(middle), semi_space_size);
   }
 
-  // Allocate the entire space at the beginning.
-  space_->Commit(false);
-
-  // Setup the semi spaces.
-  uword semi_space_size = space_->size() / 2;
-  ASSERT((semi_space_size & (VirtualMemory::PageSize() - 1)) == 0);
-  to_ = new MemoryRegion(space_->address(), semi_space_size);
-  uword middle = space_->start() + semi_space_size;
-  from_ = new MemoryRegion(reinterpret_cast<void*>(middle), semi_space_size);
-
   // Make sure that the two semi-spaces are aligned properly.
   ASSERT(Utils::IsAligned(to_->start(), kObjectAlignment));
   ASSERT(Utils::IsAligned(from_->start(), kObjectAlignment));
 
   // Setup local fields.
   top_ = FirstObjectStart();
   resolved_top_ = top_;
   end_ = to_->end();
 
   survivor_end_ = FirstObjectStart();
@@ skipping 380 matching lines @@
     OS::PrintErr(" done.\n");
   }
 
   // Done scavenging. Reset the marker.
   ASSERT(scavenging_);
   scavenging_ = false;
 }
 
 
 void Scavenger::WriteProtect(bool read_only) {
-  space_->Protect(
-      read_only ? VirtualMemory::kReadOnly : VirtualMemory::kReadWrite);
+  if (space_ != NULL) {
+    space_->Protect(
+        read_only ? VirtualMemory::kReadOnly : VirtualMemory::kReadWrite);
+  }
 }
 
 
 void Scavenger::PrintToJSONObject(JSONObject* object) {
   JSONObject space(object, "new");
   space.AddProperty("type", "@Scavenger");
   space.AddProperty("id", "heaps/new");
   space.AddProperty("name", "Scavenger");
   space.AddProperty("user_name", "new");
   space.AddProperty("collections", collections());
@@ skipping 10 matching lines @@
 }
 
 
 void Scavenger::FreeExternal(intptr_t size) {
   ASSERT(size >= 0);
   external_size_ -= size;
   ASSERT(external_size_ >= 0);
 }
 
 }  // namespace dart