Reland r24563 and r24564 with fixes cumbersome API leading to leaks.

runtime/vm/weak_table.cc

Index: runtime/vm/weak_table.cc
===================================================================
--- runtime/vm/weak_table.cc	(revision 24610)
+++ runtime/vm/weak_table.cc	(working copy)
@@ -9,21 +9,41 @@
 
 namespace dart {
 
-WeakTable* WeakTable::SetValue(RawObject* key, intptr_t val) {
-  intptr_t sz = size();
-  intptr_t idx = Hash(key) % sz;
+intptr_t WeakTable::SizeFor(intptr_t count, intptr_t size) {
+  intptr_t result = size;
+  if (count <= (size / 4)) {
+    // Reduce the capacity.
+    result = size / 2;
+  } else {
+    // Increase the capacity.
+    result = size * 2;
+    if (result < size) {
+      FATAL("Reached impossible state of having more weak table entries"
+            " than memory available for heap objects.");
+    }
+  }
+  if (result < kMinSize) {
+    result = kMinSize;
+  }
+  return result;
+}
+
+
+void WeakTable::SetValue(RawObject* key, intptr_t val) {
+  intptr_t mask = size() - 1;
+  intptr_t idx = Hash(key) & mask;
   intptr_t empty_idx = -1;
   RawObject* obj = ObjectAt(idx);
 
   while (obj != NULL) {
     if (obj == key) {
       SetValueAt(idx, val);
-      return this;
+      return;
     } else if ((empty_idx < 0) &&
                (reinterpret_cast<intptr_t>(obj) == kDeletedEntry)) {
       empty_idx = idx;  // Insert at this location if not found.
     }
-    idx = (idx + 1) % sz;
+    idx = (idx + 1) & mask;
     obj = ObjectAt(idx);
   }
 
@@ -31,7 +51,7 @@
     // Do not enter an invalid value. Associating 0 with a key deletes it from
     // this weak table above in SetValueAt. If the key was not present in the
     // weak table we are done.
-    return this;
+    return;
   }
 
   if (empty_idx >= 0) {
@@ -50,23 +70,46 @@
 
   // Rehash if needed to ensure that there are empty slots available.
   if (used_ >= limit()) {
-    return Rehash();
+    Rehash();
   }
-  return this;
 }
 
 
-WeakTable* WeakTable::Rehash() {
-  intptr_t sz = size();
-  WeakTable* result = NewFrom(this);
+void WeakTable::Rehash() {
+  intptr_t old_size = size();
+  intptr_t* old_data = data_;
 
-  for (intptr_t i = 0; i < sz; i++) {
+  intptr_t new_size = SizeFor(count(), size());
+  ASSERT(Utils::IsPowerOfTwo(new_size));
+  intptr_t* new_data = reinterpret_cast<intptr_t*>(
+      calloc(new_size, kEntrySize * kWordSize));
+
+  intptr_t mask = new_size - 1;
+  set_used(0);
+  for (intptr_t i = 0; i < old_size; i++) {
     if (IsValidEntryAt(i)) {
-      WeakTable* temp = result->SetValue(ObjectAt(i), ValueAt(i));
-      ASSERT(temp == result);
+      // Find the new hash location for this entry.
+      RawObject* key = ObjectAt(i);
+      intptr_t idx = Hash(key) & mask;
+      RawObject* obj = reinterpret_cast<RawObject*>(new_data[ObjectIndex(idx)]);
+      while (obj != NULL) {
+        ASSERT(obj != key);  // Duplicate entry is not expected.
+        idx = (idx + 1) & mask;
+        obj = reinterpret_cast<RawObject*>(new_data[ObjectIndex(idx)]);
+      }
+
+      new_data[ObjectIndex(idx)] = reinterpret_cast<intptr_t>(key);
+      new_data[ValueIndex(idx)] = ValueAt(i);
+      set_used(used() + 1);
     }
   }
-  return result;
+  // We should only have used valid entries.
+  ASSERT(used() == count());
+
+  // Switch to using the newly allocated backing store.
+  size_ = new_size;
+  data_ = new_data;
+  free(old_data);
 }
 
 }  // namespace dart