If we can't rehash the backing store for weak sets & maps, do a last resort GC

src/objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 17729 matching lines @@
   if (entry != kNotFound) {
     table->set(EntryToIndex(entry) + 1, *value);
     return table;
   }
 
   // Rehash if more than 33% of the entries are deleted entries.
   // TODO(jochen): Consider to shrink the fixed array in place.
   if ((table->NumberOfDeletedElements() << 1) > table->NumberOfElements()) {
     table->Rehash(isolate->factory()->undefined_value());
   }
+  // If we're out of luck, we didn't get a GC recently, and so rehashing
+  // isn't enough to avoid a crash.
+  int nof = table->NumberOfElements() + 1;
+  if (!table->HasSufficientCapacity(nof)) {
+    int capacity = ObjectHashTable::ComputeCapacity(nof * 2);
+    if (capacity > ObjectHashTable::kMaxCapacity) {
+      for (size_t i = 0; i < 2; ++i) {
+        isolate->heap()->CollectAllGarbage(
+            Heap::kFinalizeIncrementalMarkingMask,
+            "last resort gc (object hash table)");

[Hannes Payer (out of office), 2016/07/07 15:22:00]

let's not call this last resort gc, to not confuse it with the actual emergency
gc. just call it "full object hash table"

+      }
+      table->Rehash(isolate->factory()->undefined_value());
+    }
+  }
 
   // Check whether the hash table should be extended.
   table = EnsureCapacity(table, 1, key);
   table->AddEntry(table->FindInsertionEntry(hash), *key, *value);
   return table;
 }
 
 
 Handle<ObjectHashTable> ObjectHashTable::Remove(Handle<ObjectHashTable> table,
                                                 Handle<Object> key,
@@ skipping 1218 matching lines @@
 
   Object* data_obj =
       constructor->shared()->get_api_func_data()->access_check_info();
   if (data_obj->IsUndefined(isolate)) return nullptr;
 
   return AccessCheckInfo::cast(data_obj);
 }
 
 }  // namespace internal
 }  // namespace v8