Purge in-memory localStorage areas if the # of areas exceeds the limit

webkit/dom_storage/dom_storage_namespace.cc

 // Copyright (c) 2012 The Chromium 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 "webkit/dom_storage/dom_storage_namespace.h"
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
@@ skipping 99 matching lines @@
     area->DeleteOrigin();
   }
 }
 
 void DomStorageNamespace::DeleteSessionStorageOrigin(const GURL& origin) {
   DomStorageArea* area = OpenStorageArea(origin);
   area->FastClear();
   CloseStorageArea(area);
 }
 
+void DomStorageNamespace::PurgeUnopenedAreas() {
+  if (directory_.empty())
+    return;  // We can't purge w/o backing on disk.
+  AreaMap::iterator it = areas_.begin();
+  while (it != areas_.end()) {

[michaeln, 2013/04/05 23:39:23]

There's a block of code in PurgeMemory that i think needs to be here too. The
conditional call to continue around this comment...
// Leave it alone if changes are pending

The reason is that these area instance will get deleted/unreachable after being
erased from areas_. But there may actually be a commit in flight (to be
performed on the COMMIT sequence). If a new request comes along to access that
same area prior to that commit happening, we'll read stale data on the PRIMARY
sequence. So if there is something in flight, I don't think we want to remove it
from areas_ or drop its cache.


Maybe these two methods could be consolidated

PurgeUnopened() { PurgeHelper(false); }
PurgeMemory() { PurgeHelper(true); }

void PurgeHelper(bool aggressive) {
  ...
  if (aggressive) {
    // Otherwise, we can clear caches and such.
  }
}

[kinuko, 2013/04/10 07:04:14]

Sounds good, I consolidated the two methods.

+    if (it->second.open_count_ == 0) {
+      it->second.area_->Shutdown();
+      areas_.erase(it++);
+      continue;
+    }
+    ++it;
+  }
+}
+
 void DomStorageNamespace::PurgeMemory() {
   if (directory_.empty())
     return;  // We can't purge w/o backing on disk.
   AreaMap::iterator it = areas_.begin();
   while (it != areas_.end()) {
     // Leave it alone if changes are pending
     if (it->second.area_->HasUncommittedChanges()) {
       ++it;
       continue;
     }
@@ skipping 35 matching lines @@
 
 DomStorageNamespace::AreaHolder::AreaHolder(
     DomStorageArea* area, int count)
     : area_(area), open_count_(count) {
 }
 
 DomStorageNamespace::AreaHolder::~AreaHolder() {
 }
 
 }  // namespace dom_storage