Use clustered serialization for full snapshots.

runtime/vm/class_table.cc

Index: runtime/vm/class_table.cc
diff --git a/runtime/vm/class_table.cc b/runtime/vm/class_table.cc
index 9432a1beeeca0f7e8c84c3fc73ea41bd68379715..b04f77c7b09c8d7d0370e365ba93035b10d7b257 100644
--- a/runtime/vm/class_table.cc
+++ b/runtime/vm/class_table.cc
@@ -180,6 +180,42 @@ void ClassTable::RegisterAt(intptr_t index, const Class& cls) {
 }
 
 
+void ClassTable::RegisterAt(intptr_t index, RawClass* cls) {
+  ASSERT(Thread::Current()->IsMutatorThread());
+  ASSERT(index != kIllegalCid);
+  ASSERT(index >= kNumPredefinedCids);
+  if (index >= capacity_) {
+    // Grow the capacity of the class table.
+    // TODO(koda): Add ClassTable::Grow to share code.
+    intptr_t new_capacity = index + capacity_increment_;
+    if (!Class::is_valid_id(index) || new_capacity < capacity_) {
+      FATAL1("Fatal error in ClassTable::Register: invalid index %" Pd "\n",
+             index);
+    }
+    RawClass** new_table = reinterpret_cast<RawClass**>(
+        malloc(new_capacity * sizeof(RawClass*)));  // NOLINT
+    memmove(new_table, table_, capacity_ * sizeof(RawClass*));
+    ClassHeapStats* new_stats_table = reinterpret_cast<ClassHeapStats*>(
+        realloc(class_heap_stats_table_,
+                new_capacity * sizeof(ClassHeapStats)));  // NOLINT
+    for (intptr_t i = capacity_; i < new_capacity; i++) {
+      new_table[i] = NULL;
+      new_stats_table[i].Initialize();
+    }
+    capacity_ = new_capacity;
+    old_tables_->Add(table_);
+    table_ = new_table;  // TODO(koda): This should use atomics.
+    class_heap_stats_table_ = new_stats_table;
+    ASSERT(capacity_increment_ >= 1);
+  }
+  ASSERT(table_[index] == 0);

[siva, 2016/06/21 23:51:43]

This piece of code is duplicated here and above, maybe you should have a method
ClassTable::EnsureCapacity(intptr_t index); and move this code  there.

The callers can then use this pattern:
  EnsureCapcity(index);
  RegisterAt(index, rawcls);

Then you may not need two versions of RegisterAt

I am always nervous about having a raw pointer being available across a big
chunk of code like this.

[rmacnak, 2016/06/22 19:42:17]

Factored out as AllocateIndex, which ensures capacity and bumps top_.

+  table_[index] = cls;
+  if (index >= top_) {
+    top_ = index + 1;
+  }
+}
+
+
 #if defined(DEBUG)
 void ClassTable::Unregister(intptr_t index) {
   table_[index] = 0;