Changing the aging mechanism for script and eval caches.

src/objects.h

 // Copyright 2012 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.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 7919 matching lines @@
     return key->HashForObject(object);
   }
 
   static inline Handle<Object> AsHandle(Isolate* isolate, HashTableKey* key);
 
   static const int kPrefixSize = 0;
   static const int kEntrySize = 2;
 };
 
 
+// This cache is used in two different variants. For regexp caching, it simply
+// maps identifying info of the regexp to the cached regexp object. Scripts and
+// eval code only gets cached after a second probe for the code object. To do
+// so, on first "put" only a hash identifying the source is entered into the
+// cache, mapping it to a lifetime count of the hash. On each call to Age all
+// such lifetimes get reduced, and removed once they reach zero. If a second put
+// is called while such a hash is live in the cache, the hash gets replaced by
+// an actual cache entry. Age also removes stale live entries from the cache.
+// Such entries are identified by SharedFunctionInfos pointing to either the
+// recompilation stub, or to "old" code. This avoids memory leaks due to
+// premature caching of scripts and eval strings that are never needed later.
 class CompilationCacheTable: public HashTable<CompilationCacheTable,
                                               CompilationCacheShape,
                                               HashTableKey*> {
  public:
   // Find cached value for a string key, otherwise return null.
   Handle<Object> Lookup(Handle<String> src, Handle<Context> context);
   Handle<Object> LookupEval(Handle<String> src,
                             Handle<SharedFunctionInfo> shared,
                             StrictMode strict_mode, int scope_position);
   Handle<Object> LookupRegExp(Handle<String> source, JSRegExp::Flags flags);
   static Handle<CompilationCacheTable> Put(
       Handle<CompilationCacheTable> cache, Handle<String> src,
       Handle<Context> context, Handle<Object> value);
   static Handle<CompilationCacheTable> PutEval(
       Handle<CompilationCacheTable> cache, Handle<String> src,
       Handle<SharedFunctionInfo> context, Handle<SharedFunctionInfo> value,
       int scope_position);
   static Handle<CompilationCacheTable> PutRegExp(
       Handle<CompilationCacheTable> cache, Handle<String> src,
       JSRegExp::Flags flags, Handle<FixedArray> value);
   void Remove(Object* value);
+  void Age();
+  static const int kHashGenerations = 10;
 
   DECLARE_CAST(CompilationCacheTable)
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(CompilationCacheTable);
 };
 
 
 class CodeCache: public Struct {
  public:
@@ skipping 2938 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_