Flush number string cache on GC (bug 1605). Also start with a small

src/heap.cc

Index: src/heap.cc
===================================================================
--- src/heap.cc	(revision 10495)
+++ src/heap.cc	(working copy)
@@ -896,8 +896,7 @@
 
   CompletelyClearInstanceofCache();
 
-  // TODO(1605) select heuristic for flushing NumberString cache with
-  // FlushNumberStringCache
+  FlushNumberStringCache();

[Michael Starzinger, 2012/01/25 13:00:56]

If it's intentional that the new heuristic for flushing is "always flush", then
I am fine with that. Please document that in the issue tracker.

[Erik Corry, 2012/01/25 14:37:26]

Done.

   if (FLAG_cleanup_code_caches_at_gc) {
     polymorphic_code_cache()->set_cache(undefined_value());
   }
@@ -2506,7 +2505,10 @@
   }
   set_intrinsic_function_names(StringDictionary::cast(obj));
 
-  if (InitializeNumberStringCache()->IsFailure()) return false;
+  { MaybeObject* maybe_obj = AllocateInitialNumberStringCache();
+    if (!maybe_obj->ToObject(&obj)) return false;
+  }
+  set_number_string_cache(FixedArray::cast(obj));
 
   // Allocate cache for single character ASCII strings.
   { MaybeObject* maybe_obj =
@@ -2616,17 +2618,35 @@
 }
 
 
-MaybeObject* Heap::InitializeNumberStringCache() {
+MaybeObject* Heap::AllocateInitialNumberStringCache() {
+  MaybeObject* maybe_obj =
+      AllocateFixedArray(kInitialNumberStringCacheSize * 2, TENURED);
+  return maybe_obj;
+}
+
+
+int Heap::FullSizeNumberStringCacheLength() {
   // Compute the size of the number string cache based on the max heap size.
   // max_semispace_size_ == 512 KB => number_string_cache_size = 32.

[Michael Starzinger, 2012/01/25 13:00:56]

This comment no longer is on sync with the computation below.

[Erik Corry, 2012/01/25 14:37:26]

Done.

   // max_semispace_size_ ==   8 MB => number_string_cache_size = 16KB.
   int number_string_cache_size = max_semispace_size_ / 512;
-  number_string_cache_size = Max(32, Min(16*KB, number_string_cache_size));
-  Object* obj;
+  number_string_cache_size = Max(kInitialNumberStringCacheSize * 2,

[Michael Starzinger, 2012/01/25 13:00:56]

The constant is multiplied with 2 twice. I think we can drop this
multiplication.

[Erik Corry, 2012/01/25 14:37:26]

The first multiplication is there to ensure that the full size is always bigger
than the initial size.  The second is there because there is a string and a
number per entry so the length has to be twice the size (in entries).  Comments
have been updated.

+                                 Min(16*KB, number_string_cache_size));
+  return number_string_cache_size * 2;
+}
+
+
+void Heap::AllocateFullSizeNumberStringCache() {
+  // The idea is to have a small number string cache in the snapshot to keep
+  // boot-time memory usage down.  If we expand the number string cache already
+  // while creating the snapshot then that didn't work out.
+  ASSERT(!Serializer::enabled());
   MaybeObject* maybe_obj =
-      AllocateFixedArray(number_string_cache_size * 2, TENURED);
-  if (maybe_obj->ToObject(&obj)) set_number_string_cache(FixedArray::cast(obj));
-  return maybe_obj;
+      AllocateFixedArray(FullSizeNumberStringCacheLength(), TENURED);
+  Object* new_cache;
+  if (maybe_obj->ToObject(&new_cache)) {

[Michael Starzinger, 2012/01/25 13:00:56]

Can we add a comment that this is a best effort allocation and we ignore
failures here?

[Erik Corry, 2012/01/25 14:37:26]

Done.

+    set_number_string_cache(FixedArray::cast(new_cache));
+  }
 }
 
 
@@ -2675,11 +2695,17 @@
   int mask = (number_string_cache()->length() >> 1) - 1;
   if (number->IsSmi()) {
     hash = smi_get_hash(Smi::cast(number)) & mask;
-    number_string_cache()->set(hash * 2, Smi::cast(number));
   } else {
     hash = double_get_hash(number->Number()) & mask;
-    number_string_cache()->set(hash * 2, number);
   }
+  if (number_string_cache()->get(hash * 2) != undefined_value() &&
+      number_string_cache()->length() != FullSizeNumberStringCacheLength()) {
+    // The first time we have a hash collision, we move to the full sized
+    // number string cache.
+    AllocateFullSizeNumberStringCache();
+    return;
+  }
+  number_string_cache()->set(hash * 2, number);
   number_string_cache()->set(hash * 2 + 1, string);
 }