Better session restore: Persist sessionStorage on disk.

Write sessionStorage on disk, and restore it after
relaunching, when recovering from a crash, and when the
startup option "continue where I left off" is selected.

BUG=104292
TEST=Manual; SessionStorageDatabaseTest.ReadOriginsInNamespace


Review URL: https://chromiumcodereview.appspot.com/9963107

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@150314 0039d316-1c4b-4281-b951-d872f2087c98

10 files changed, 334 insertions, 53 deletions

diff --git a/webkit/dom_storage/dom_storage_area.cc b/webkit/dom_storage/dom_storage_area.cc
index a532194..734edff 100644
--- a/webkit/dom_storage/dom_storage_area.cc
+++ b/webkit/dom_storage/dom_storage_area.cc
@@ -15,6 +15,8 @@
 #include "webkit/dom_storage/dom_storage_task_runner.h"
 #include "webkit/dom_storage/dom_storage_types.h"
 #include "webkit/dom_storage/local_storage_database_adapter.h"
+#include "webkit/dom_storage/session_storage_database.h"
+#include "webkit/dom_storage/session_storage_database_adapter.h"
 #include "webkit/fileapi/file_system_util.h"
 #include "webkit/glue/webkit_glue.h"
 
@@ -72,16 +74,23 @@ DomStorageArea::DomStorageArea(
     int64 namespace_id,
     const std::string& persistent_namespace_id,
     const GURL& origin,
+    SessionStorageDatabase* session_storage_backing,
     DomStorageTaskRunner* task_runner)
     : namespace_id_(namespace_id),
       persistent_namespace_id_(persistent_namespace_id),
       origin_(origin),
       task_runner_(task_runner),
       map_(new DomStorageMap(kPerAreaQuota + kPerAreaOverQuotaAllowance)),
+      session_storage_backing_(session_storage_backing),
       is_initial_import_done_(true),
       is_shutdown_(false),
       commit_batches_in_flight_(0) {
   DCHECK(namespace_id != kLocalStorageNamespaceId);
+  if (session_storage_backing) {
+    backing_.reset(new SessionStorageDatabaseAdapter(
+        session_storage_backing, persistent_namespace_id, origin));
+    is_initial_import_done_ = false;
+  }
 }
 
 DomStorageArea::~DomStorageArea() {
@@ -168,13 +177,20 @@ DomStorageArea* DomStorageArea::ShallowCopy(
     const std::string& destination_persistent_namespace_id) {
   DCHECK_NE(kLocalStorageNamespaceId, namespace_id_);
   DCHECK_NE(kLocalStorageNamespaceId, destination_namespace_id);
-  DCHECK(!backing_.get());  // SessionNamespaces aren't stored on disk.
 
   DomStorageArea* copy = new DomStorageArea(
       destination_namespace_id, destination_persistent_namespace_id, origin_,
-      task_runner_);
+      session_storage_backing_, task_runner_);
   copy->map_ = map_;
   copy->is_shutdown_ = is_shutdown_;
+  copy->is_initial_import_done_ = true;
+
+  // All the uncommitted changes to this area need to happen before the actual
+  // shallow copy is made (scheduled by the upper layer). Another OnCommitTimer
+  // call might be in the event queue at this point, but it's handled gracefully
+  // when it fires.
+  if (commit_batch_.get())
+    OnCommitTimer();
   return copy;
 }
 
@@ -185,6 +201,8 @@ bool DomStorageArea::HasUncommittedChanges() const {
 
 void DomStorageArea::DeleteOrigin() {
   DCHECK(!is_shutdown_);
+  // This function shouldn't be called for sessionStorage.
+  DCHECK(!session_storage_backing_.get());
   if (HasUncommittedChanges()) {
     // TODO(michaeln): This logically deletes the data immediately,
     // and in a matter of a second, deletes the rows from the backing
@@ -236,7 +254,6 @@ void DomStorageArea::InitialImportIfNeeded() {
   if (is_initial_import_done_)
     return;
 
-  DCHECK_EQ(kLocalStorageNamespaceId, namespace_id_);
   DCHECK(backing_.get());
 
   ValuesMap initial_values;
@@ -264,13 +281,15 @@ DomStorageArea::CommitBatch* DomStorageArea::CreateCommitBatchIfNeeded() {
 }
 
 void DomStorageArea::OnCommitTimer() {
-  DCHECK_EQ(kLocalStorageNamespaceId, namespace_id_);
   if (is_shutdown_)
     return;
 
   DCHECK(backing_.get());
-  DCHECK(commit_batch_.get());
-  DCHECK(!commit_batches_in_flight_);
+
+  // It's possible that there is nothing to commit, since a shallow copy occured
+  // before the timer fired.
+  if (!commit_batch_.get())
+    return;
 
   // This method executes on the primary sequence, we schedule
   // a task for immediate execution on the commit sequence.
@@ -298,9 +317,9 @@ void DomStorageArea::CommitChanges(const CommitBatch* commit_batch) {
 void DomStorageArea::OnCommitComplete() {
   // We're back on the primary sequence in this method.
   DCHECK(task_runner_->IsRunningOnPrimarySequence());
+  --commit_batches_in_flight_;
   if (is_shutdown_)
     return;
-  --commit_batches_in_flight_;
   if (commit_batch_.get() && !commit_batches_in_flight_) {
     // More changes have accrued, restart the timer.
     task_runner_->PostDelayedTask(
@@ -323,6 +342,7 @@ void DomStorageArea::ShutdownInCommitSequence() {
   }
   commit_batch_.reset();
   backing_.reset();
+  session_storage_backing_ = NULL;
 }
 
 }  // namespace dom_storage
diff --git a/webkit/dom_storage/dom_storage_area.h b/webkit/dom_storage/dom_storage_area.h
index 1dbf31c..7a17901 100644
--- a/webkit/dom_storage/dom_storage_area.h
+++ b/webkit/dom_storage/dom_storage_area.h
@@ -19,6 +19,7 @@ namespace dom_storage {
 class DomStorageDatabaseAdapter;
 class DomStorageMap;
 class DomStorageTaskRunner;
+class SessionStorageDatabase;
 
 // Container for a per-origin Map of key/value pairs potentially
 // backed by storage on disk and lazily commits changes to disk.
@@ -36,10 +37,11 @@ class DomStorageArea
                  const FilePath& directory,
                  DomStorageTaskRunner* task_runner);
 
-  // Session storage.
+  // Session storage. Backed on disk if |session_storage_backing| is not NULL.
   DomStorageArea(int64 namespace_id,
                  const std::string& persistent_namespace_id,
                  const GURL& origin,
+                 SessionStorageDatabase* session_storage_backing,
                  DomStorageTaskRunner* task_runner);
 
   const GURL& origin() const { return origin_; }
@@ -119,6 +121,7 @@ class DomStorageArea
   scoped_refptr<DomStorageTaskRunner> task_runner_;
   scoped_refptr<DomStorageMap> map_;
   scoped_ptr<DomStorageDatabaseAdapter> backing_;
+  scoped_refptr<SessionStorageDatabase> session_storage_backing_;
   bool is_initial_import_done_;
   bool is_shutdown_;
   scoped_ptr<CommitBatch> commit_batch_;
diff --git a/webkit/dom_storage/dom_storage_area_unittest.cc b/webkit/dom_storage/dom_storage_area_unittest.cc
index e41b080..5d2e953 100644
--- a/webkit/dom_storage/dom_storage_area_unittest.cc
+++ b/webkit/dom_storage/dom_storage_area_unittest.cc
@@ -73,7 +73,7 @@ class DomStorageAreaTest : public testing::Test {
 
 TEST_F(DomStorageAreaTest, DomStorageAreaBasics) {
   scoped_refptr<DomStorageArea> area(
-      new DomStorageArea(1, std::string(), kOrigin, NULL));
+      new DomStorageArea(1, std::string(), kOrigin, NULL, NULL));
   string16 old_value;
   NullableString16 old_nullable_value;
   scoped_refptr<DomStorageArea> copy;
@@ -138,12 +138,12 @@ TEST_F(DomStorageAreaTest, BackingDatabaseOpened) {
     EXPECT_FALSE(file_util::PathExists(kExpectedOriginFilePath));
   }
 
-  // Valid directory and origin but non-local namespace id. Backing should
+  // Valid directory and origin but no session storage backing. Backing should
   // be null.
   {
     scoped_refptr<DomStorageArea> area(
         new DomStorageArea(kSessionStorageNamespaceId, std::string(), kOrigin,
-                           NULL));
+                           NULL, NULL));
     EXPECT_EQ(NULL, area->backing_.get());
     EXPECT_TRUE(area->is_initial_import_done_);
 
diff --git a/webkit/dom_storage/dom_storage_context.cc b/webkit/dom_storage/dom_storage_context.cc
index 9d431ba..4e46c89 100644
--- a/webkit/dom_storage/dom_storage_context.cc
+++ b/webkit/dom_storage/dom_storage_context.cc
@@ -15,12 +15,15 @@
 #include "webkit/dom_storage/dom_storage_namespace.h"
 #include "webkit/dom_storage/dom_storage_task_runner.h"
 #include "webkit/dom_storage/dom_storage_types.h"
+#include "webkit/dom_storage/session_storage_database.h"
 #include "webkit/quota/special_storage_policy.h"
 
 using file_util::FileEnumerator;
 
 namespace dom_storage {
 
+static const int kSessionStoraceScavengingSeconds = 60;
+
 DomStorageContext::UsageInfo::UsageInfo() : data_size(0) {}
 DomStorageContext::UsageInfo::~UsageInfo() {}
 
@@ -34,7 +37,8 @@ DomStorageContext::DomStorageContext(
       task_runner_(task_runner),
       is_shutdown_(false),
       force_keep_session_state_(false),
-      special_storage_policy_(special_storage_policy) {
+      special_storage_policy_(special_storage_policy),
+      scavenging_started_(false) {
   // AtomicSequenceNum starts at 0 but we want to start session
   // namespace ids at one since zero is reserved for the
   // kLocalStorageNamespaceId.
@@ -88,6 +92,7 @@ void DomStorageContext::GetUsageInfo(std::vector<UsageInfo>* infos,
       infos->push_back(info);
     }
   }
+  // TODO(marja): Get usage infos for sessionStorage (crbug.com/123599).
 }
 
 void DomStorageContext::DeleteOrigin(const GURL& origin) {
@@ -111,7 +116,7 @@ void DomStorageContext::Shutdown() {
   for (; it != namespaces_.end(); ++it)
     it->second->Shutdown();
 
-  if (localstorage_directory_.empty())
+  if (localstorage_directory_.empty() && !session_storage_database_.get())
     return;
 
   // Respect the content policy settings about what to
@@ -186,13 +191,31 @@ void DomStorageContext::CreateSessionNamespace(
   DCHECK(namespace_id != kLocalStorageNamespaceId);
   DCHECK(namespaces_.find(namespace_id) == namespaces_.end());
   namespaces_[namespace_id] = new DomStorageNamespace(
-      namespace_id, persistent_namespace_id, task_runner_);
+      namespace_id, persistent_namespace_id, session_storage_database_.get(),
+      task_runner_);
 }
 
 void DomStorageContext::DeleteSessionNamespace(
     int64 namespace_id, bool should_persist_data) {
   DCHECK_NE(kLocalStorageNamespaceId, namespace_id);
-  // TODO(marja): Protect the sessionStorage data (once it's written on disk).
+  StorageNamespaceMap::const_iterator it = namespaces_.find(namespace_id);
+  if (it == namespaces_.end())
+    return;
+  if (session_storage_database_.get()) {
+    std::string persistent_namespace_id = it->second->persistent_namespace_id();
+    if (!should_persist_data) {
+      task_runner_->PostShutdownBlockingTask(
+          FROM_HERE,
+          DomStorageTaskRunner::COMMIT_SEQUENCE,
+          base::Bind(
+              base::IgnoreResult(&SessionStorageDatabase::DeleteNamespace),
+              session_storage_database_,
+              persistent_namespace_id));
+    } else if (!scavenging_started_) {
+      // Protect the persistent namespace ID from scavenging.
+      protected_persistent_session_ids_.insert(persistent_namespace_id);
+    }
+  }
   namespaces_.erase(namespace_id);
 }
 
@@ -211,23 +234,124 @@ void DomStorageContext::CloneSessionNamespace(
 }
 
 void DomStorageContext::ClearSessionOnlyOrigins() {
-  std::vector<UsageInfo> infos;
-  const bool kDontIncludeFileInfo = false;
-  GetUsageInfo(&infos, kDontIncludeFileInfo);
-  for (size_t i = 0; i < infos.size(); ++i) {
-    const GURL& origin = infos[i].origin;
-    if (special_storage_policy_->IsStorageProtected(origin))
-      continue;
-    if (!special_storage_policy_->IsStorageSessionOnly(origin))
-      continue;
-
-    const bool kNotRecursive = false;
-    FilePath database_file_path = localstorage_directory_.Append(
-        DomStorageArea::DatabaseFileNameFromOrigin(origin));
-    file_util::Delete(database_file_path, kNotRecursive);
-    file_util::Delete(
-        DomStorageDatabase::GetJournalFilePath(database_file_path),
-        kNotRecursive);
+  if (!localstorage_directory_.empty()) {
+    std::vector<UsageInfo> infos;
+    const bool kDontIncludeFileInfo = false;
+    GetUsageInfo(&infos, kDontIncludeFileInfo);
+    for (size_t i = 0; i < infos.size(); ++i) {
+      const GURL& origin = infos[i].origin;
+      if (special_storage_policy_->IsStorageProtected(origin))
+        continue;
+      if (!special_storage_policy_->IsStorageSessionOnly(origin))
+        continue;
+
+      const bool kNotRecursive = false;
+      FilePath database_file_path = localstorage_directory_.Append(
+          DomStorageArea::DatabaseFileNameFromOrigin(origin));
+      file_util::Delete(database_file_path, kNotRecursive);
+      file_util::Delete(
+          DomStorageDatabase::GetJournalFilePath(database_file_path),
+          kNotRecursive);
+    }
+  }
+  if (session_storage_database_.get()) {
+    std::vector<std::string> namespace_ids;
+    session_storage_database_->ReadNamespaceIds(&namespace_ids);
+    for (std::vector<std::string>::const_iterator it = namespace_ids.begin();
+         it != namespace_ids.end(); ++it) {
+      std::vector<GURL> origins;
+      session_storage_database_->ReadOriginsInNamespace(*it, &origins);
+
+      for (std::vector<GURL>::const_iterator origin_it = origins.begin();
+           origin_it != origins.end(); ++origin_it) {
+        if (special_storage_policy_->IsStorageProtected(*origin_it))
+          continue;
+        if (!special_storage_policy_->IsStorageSessionOnly(*origin_it))
+          continue;
+        session_storage_database_->DeleteArea(*it, *origin_it);
+      }
+    }
+  }
+}
+
+void DomStorageContext::SetSaveSessionStorageOnDisk() {
+  DCHECK(namespaces_.empty());
+  if (!sessionstorage_directory_.empty()) {
+    session_storage_database_ = new SessionStorageDatabase(
+        sessionstorage_directory_);
+  }
+}
+
+void DomStorageContext::StartScavengingUnusedSessionStorage() {
+  if (session_storage_database_.get()) {
+    task_runner_->PostDelayedTask(
+        FROM_HERE, base::Bind(&DomStorageContext::FindUnusedNamespaces, this),
+        base::TimeDelta::FromSeconds(kSessionStoraceScavengingSeconds));
+  }
+}
+
+void DomStorageContext::FindUnusedNamespaces() {
+  DCHECK(session_storage_database_.get());
+  DCHECK(!scavenging_started_);
+  scavenging_started_ = true;
+  std::set<std::string> namespace_ids_in_use;
+  for (StorageNamespaceMap::const_iterator it = namespaces_.begin();
+       it != namespaces_.end(); ++it)
+    namespace_ids_in_use.insert(it->second->persistent_namespace_id());
+  std::set<std::string> protected_persistent_session_ids;
+  protected_persistent_session_ids.swap(protected_persistent_session_ids_);
+  task_runner_->PostShutdownBlockingTask(
+      FROM_HERE, DomStorageTaskRunner::COMMIT_SEQUENCE,
+      base::Bind(
+          &DomStorageContext::FindUnusedNamespacesInCommitSequence,
+          this, namespace_ids_in_use, protected_persistent_session_ids));
+}
+
+void DomStorageContext::FindUnusedNamespacesInCommitSequence(
+    const std::set<std::string>& namespace_ids_in_use,
+    const std::set<std::string>& protected_persistent_session_ids) {
+  DCHECK(session_storage_database_.get());
+  // Delete all namespaces which don't have an associated DomStorageNamespace
+  // alive.
+  std::vector<std::string> namespace_ids;
+  session_storage_database_->ReadNamespaceIds(&namespace_ids);
+  for (std::vector<std::string>::const_iterator it = namespace_ids.begin();
+       it != namespace_ids.end(); ++it) {
+    if (namespace_ids_in_use.find(*it) == namespace_ids_in_use.end() &&
+        protected_persistent_session_ids.find(*it) ==
+        protected_persistent_session_ids.end()) {
+      deletable_persistent_namespace_ids_.push_back(*it);
+    }
+  }
+  if (!deletable_persistent_namespace_ids_.empty()) {
+    task_runner_->PostDelayedTask(
+        FROM_HERE, base::Bind(
+            &DomStorageContext::DeleteNextUnusedNamespace,
+            this),
+        base::TimeDelta::FromSeconds(kSessionStoraceScavengingSeconds));
+  }
+}
+
+void DomStorageContext::DeleteNextUnusedNamespace() {
+  if (is_shutdown_)
+    return;
+  task_runner_->PostShutdownBlockingTask(
+        FROM_HERE, DomStorageTaskRunner::COMMIT_SEQUENCE,
+        base::Bind(
+            &DomStorageContext::DeleteNextUnusedNamespaceInCommitSequence,
+            this));
+}
+
+void DomStorageContext::DeleteNextUnusedNamespaceInCommitSequence() {
+  const std::string& persistent_id = deletable_persistent_namespace_ids_.back();
+  session_storage_database_->DeleteNamespace(persistent_id);
+  deletable_persistent_namespace_ids_.pop_back();
+  if (!deletable_persistent_namespace_ids_.empty()) {
+    task_runner_->PostDelayedTask(
+        FROM_HERE, base::Bind(
+            &DomStorageContext::DeleteNextUnusedNamespace,
+            this),
+        base::TimeDelta::FromSeconds(kSessionStoraceScavengingSeconds));
   }
 }
 
diff --git a/webkit/dom_storage/dom_storage_context.h b/webkit/dom_storage/dom_storage_context.h
index 5860ec9..d2b94d4 100644
--- a/webkit/dom_storage/dom_storage_context.h
+++ b/webkit/dom_storage/dom_storage_context.h
@@ -6,6 +6,7 @@
 #define WEBKIT_DOM_STORAGE_DOM_STORAGE_CONTEXT_H_
 
 #include <map>
+#include <set>
 #include <vector>
 
 #include "base/atomic_sequence_num.h"
@@ -34,6 +35,7 @@ class DomStorageArea;
 class DomStorageNamespace;
 class DomStorageSession;
 class DomStorageTaskRunner;
+class SessionStorageDatabase;
 
 // The Context is the root of an object containment hierachy for
 // Namespaces and Areas related to the owning profile.
@@ -159,6 +161,15 @@ class DomStorageContext
   void CloneSessionNamespace(int64 existing_id, int64 new_id,
                              const std::string& new_persistent_id);
 
+  // Starts backing sessionStorage on disk. This function must be called right
+  // after DomStorageContext is created, before it's used.
+  void SetSaveSessionStorageOnDisk();
+
+  // Deletes all namespaces which don't have an associated DomStorageNamespace
+  // alive. This function is used for deleting possible leftover data after an
+  // unclean exit.
+  void StartScavengingUnusedSessionStorage();
+
  private:
   friend class DomStorageContextTest;
   FRIEND_TEST_ALL_PREFIXES(DomStorageContextTest, Basics);
@@ -170,6 +181,14 @@ class DomStorageContext
 
   void ClearSessionOnlyOrigins();
 
+  // For scavenging unused sessionStorages.
+  void FindUnusedNamespaces();
+  void FindUnusedNamespacesInCommitSequence(
+      const std::set<std::string>& namespace_ids_in_use,
+      const std::set<std::string>& protected_persistent_session_ids);
+  void DeleteNextUnusedNamespace();
+  void DeleteNextUnusedNamespaceInCommitSequence();
+
   // Collection of namespaces keyed by id.
   StorageNamespaceMap namespaces_;
 
@@ -194,6 +213,15 @@ class DomStorageContext
   bool is_shutdown_;
   bool force_keep_session_state_;
   scoped_refptr<quota::SpecialStoragePolicy> special_storage_policy_;
+  scoped_refptr<SessionStorageDatabase> session_storage_database_;
+
+  // For cleaning up unused namespaces gradually.
+  bool scavenging_started_;
+  std::vector<std::string> deletable_persistent_namespace_ids_;
+
+  // Persistent namespace IDs to protect from gradual deletion (they will
+  // be needed for session restore).
+  std::set<std::string> protected_persistent_session_ids_;
 };
 
 }  // namespace dom_storage
diff --git a/webkit/dom_storage/dom_storage_namespace.cc b/webkit/dom_storage/dom_storage_namespace.cc
index 350444c..693954c 100644
--- a/webkit/dom_storage/dom_storage_namespace.cc
+++ b/webkit/dom_storage/dom_storage_namespace.cc
@@ -5,10 +5,13 @@
 #include "webkit/dom_storage/dom_storage_namespace.h"
 
 #include "base/basictypes.h"
+#include "base/bind.h"
+#include "base/location.h"
 #include "base/logging.h"
 #include "webkit/dom_storage/dom_storage_area.h"
 #include "webkit/dom_storage/dom_storage_task_runner.h"
 #include "webkit/dom_storage/dom_storage_types.h"
+#include "webkit/dom_storage/session_storage_database.h"
 
 namespace dom_storage {
 
@@ -23,10 +26,12 @@ DomStorageNamespace::DomStorageNamespace(
 DomStorageNamespace::DomStorageNamespace(
     int64 namespace_id,
     const std::string& persistent_namespace_id,
+    SessionStorageDatabase* session_storage_database,
     DomStorageTaskRunner* task_runner)
     : namespace_id_(namespace_id),
       persistent_namespace_id_(persistent_namespace_id),
-      task_runner_(task_runner) {
+      task_runner_(task_runner),
+      session_storage_database_(session_storage_database) {
   DCHECK_NE(kLocalStorageNamespaceId, namespace_id);
 }
 
@@ -43,7 +48,7 @@ DomStorageArea* DomStorageNamespace::OpenStorageArea(const GURL& origin) {
     area = new DomStorageArea(origin, directory_, task_runner_);
   } else {
     area = new DomStorageArea(namespace_id_, persistent_namespace_id_, origin,
-                              task_runner_);
+                              session_storage_database_, task_runner_);
   }
   areas_[origin] = AreaHolder(area, 1);
   return area;
@@ -64,17 +69,29 @@ DomStorageNamespace* DomStorageNamespace::Clone(
   DCHECK_NE(kLocalStorageNamespaceId, namespace_id_);
   DCHECK_NE(kLocalStorageNamespaceId, clone_namespace_id);
   DomStorageNamespace* clone = new DomStorageNamespace(
-      clone_namespace_id, clone_persistent_namespace_id, task_runner_);
+      clone_namespace_id, clone_persistent_namespace_id,
+      session_storage_database_, task_runner_);
   AreaMap::const_iterator it = areas_.begin();
+  // Clone the in-memory structures.
   for (; it != areas_.end(); ++it) {
     DomStorageArea* area = it->second.area_->ShallowCopy(
         clone_namespace_id, clone_persistent_namespace_id);
     clone->areas_[it->first] = AreaHolder(area, 0);
   }
+  // And clone the on-disk structures, too.
+  if (session_storage_database_.get()) {
+    task_runner_->PostShutdownBlockingTask(
+        FROM_HERE,
+        DomStorageTaskRunner::COMMIT_SEQUENCE,
+        base::Bind(base::IgnoreResult(&SessionStorageDatabase::CloneNamespace),
+                   session_storage_database_.get(), persistent_namespace_id_,
+                   clone_persistent_namespace_id));
+  }
   return clone;
 }
 
 void DomStorageNamespace::DeleteOrigin(const GURL& origin) {
+  DCHECK(!session_storage_database_.get());
   AreaHolder* holder = GetAreaHolder(origin);
   if (holder) {
     holder->area_->DeleteOrigin();
diff --git a/webkit/dom_storage/dom_storage_namespace.h b/webkit/dom_storage/dom_storage_namespace.h
index 7f2f37c..ecc0f92 100644
--- a/webkit/dom_storage/dom_storage_namespace.h
+++ b/webkit/dom_storage/dom_storage_namespace.h
@@ -17,6 +17,7 @@ namespace dom_storage {
 
 class DomStorageArea;
 class DomStorageTaskRunner;
+class SessionStorageDatabase;
 
 // Container for the set of per-origin Areas.
 // See class comments for DomStorageContext for a larger overview.
@@ -28,10 +29,11 @@ class DomStorageNamespace
   DomStorageNamespace(const FilePath& directory,  // may be empty
                       DomStorageTaskRunner* task_runner);
 
-  // Constructor for a SessionStorage namespace with a non-zero id
-  // and no backing directory on disk.
+  // Constructor for a SessionStorage namespace with a non-zero id and an
+  // optional backing on disk via |session_storage_database| (may be NULL).
   DomStorageNamespace(int64 namespace_id,
                       const std::string& persistent_namespace_id,
+                      SessionStorageDatabase* session_storage_database,
                       DomStorageTaskRunner* task_runner);
 
   int64 namespace_id() const { return namespace_id_; }
@@ -79,6 +81,7 @@ class DomStorageNamespace
   FilePath directory_;
   AreaMap areas_;
   scoped_refptr<DomStorageTaskRunner> task_runner_;
+  scoped_refptr<SessionStorageDatabase> session_storage_database_;
 };
 
 }  // namespace dom_storage
diff --git a/webkit/dom_storage/session_storage_database.cc b/webkit/dom_storage/session_storage_database.cc
index 0f01db7..da3fb4b 100644
--- a/webkit/dom_storage/session_storage_database.cc
+++ b/webkit/dom_storage/session_storage_database.cc
@@ -52,12 +52,20 @@ void SessionStorageDatabase::ReadAreaValues(const std::string& namespace_id,
   // nothing to be added to the result.
   if (!LazyOpen(false))
     return;
+
+  // While ReadAreaValues is in progress, another thread can call
+  // CommitAreaChanges. CommitAreaChanges might update map ref count key while
+  // this thread is iterating over the map ref count key. To protect the reading
+  // operation, create a snapshot and read from it.
+  leveldb::ReadOptions options;
+  options.snapshot = db_->GetSnapshot();
+
   std::string map_id;
   bool exists;
-  if (!GetMapForArea(namespace_id, origin.spec(), &exists, &map_id))
-    return;
-  if (exists)
-    ReadMap(map_id, result, false);
+  if (GetMapForArea(namespace_id, origin.spec(), options, &exists, &map_id) &&
+      exists)
+    ReadMap(map_id, options, result, false);
+  db_->ReleaseSnapshot(options.snapshot);
 }
 
 bool SessionStorageDatabase::CommitAreaChanges(const std::string& namespace_id,
@@ -78,7 +86,8 @@ bool SessionStorageDatabase::CommitAreaChanges(const std::string& namespace_id,
 
   std::string map_id;
   bool exists;
-  if (!GetMapForArea(namespace_id, origin.spec(), &exists, &map_id))
+  if (!GetMapForArea(namespace_id, origin.spec(), leveldb::ReadOptions(),
+                     &exists, &map_id))
     return false;
   if (exists) {
     int64 ref_count;
@@ -192,7 +201,9 @@ bool SessionStorageDatabase::ReadNamespaceIds(
   std::string namespace_prefix = NamespacePrefix();
   scoped_ptr<leveldb::Iterator> it(db_->NewIterator(leveldb::ReadOptions()));
   it->Seek(namespace_prefix);
-  if (it->status().IsNotFound())
+  // If the key is not found, the status of the iterator won't be IsNotFound(),
+  // but the iterator will be invalid.
+  if (!it->Valid())
     return true;
 
   if (!DatabaseErrorCheck(it->status().ok()))
@@ -223,6 +234,17 @@ bool SessionStorageDatabase::ReadNamespaceIds(
   return true;
 }
 
+bool SessionStorageDatabase::ReadOriginsInNamespace(
+    const std::string& namespace_id, std::vector<GURL>* origins) {
+  std::map<std::string, std::string> areas;
+  if (!GetAreasInNamespace(namespace_id, &areas))
+    return false;
+  for (std::map<std::string, std::string>::const_iterator it = areas.begin();
+       it != areas.end(); ++it)
+    origins->push_back(GURL(it->first));
+  return true;
+}
+
 bool SessionStorageDatabase::LazyOpen(bool create_if_needed) {
   base::AutoLock auto_lock(db_lock_);
   if (db_error_ || is_inconsistent_) {
@@ -337,7 +359,9 @@ bool SessionStorageDatabase::GetAreasInNamespace(
   std::string namespace_start_key = NamespaceStartKey(namespace_id);
   scoped_ptr<leveldb::Iterator> it(db_->NewIterator(leveldb::ReadOptions()));
   it->Seek(namespace_start_key);
-  if (it->status().IsNotFound()) {
+  // If the key is not found, the status of the iterator won't be IsNotFound(),
+  // but the iterator will be invalid.
+  if (!it->Valid()) {
     // The namespace_start_key is not found when the namespace doesn't contain
     // any areas. We don't need to do anything.
     return true;
@@ -373,7 +397,8 @@ bool SessionStorageDatabase::DeleteAreaHelper(
     leveldb::WriteBatch* batch) {
   std::string map_id;
   bool exists;
-  if (!GetMapForArea(namespace_id, origin, &exists, &map_id))
+  if (!GetMapForArea(namespace_id, origin, leveldb::ReadOptions(), &exists,
+                     &map_id))
     return false;
   if (!exists)
     return true;  // Nothing to delete.
@@ -386,9 +411,10 @@ bool SessionStorageDatabase::DeleteAreaHelper(
 
 bool SessionStorageDatabase::GetMapForArea(const std::string& namespace_id,
                                            const std::string& origin,
+                                           const leveldb::ReadOptions& options,
                                            bool* exists, std::string* map_id) {
   std::string namespace_key = NamespaceKey(namespace_id, origin);
-  leveldb::Status s = db_->Get(leveldb::ReadOptions(), namespace_key, map_id);
+  leveldb::Status s = db_->Get(options, namespace_key, map_id);
   if (s.IsNotFound()) {
     *exists = false;
     return true;
@@ -421,13 +447,16 @@ bool SessionStorageDatabase::CreateMapForArea(const std::string& namespace_id,
 }
 
 bool SessionStorageDatabase::ReadMap(const std::string& map_id,
+                                     const leveldb::ReadOptions& options,
                                      ValuesMap* result,
                                      bool only_keys) {
-  scoped_ptr<leveldb::Iterator> it(db_->NewIterator(leveldb::ReadOptions()));
+  scoped_ptr<leveldb::Iterator> it(db_->NewIterator(options));
   std::string map_start_key = MapRefCountKey(map_id);
   it->Seek(map_start_key);
-  // The map needs to exist, otherwise we have a stale map_id in the database.
-  if (!ConsistencyCheck(!it->status().IsNotFound()))
+  // If the key is not found, the status of the iterator won't be IsNotFound(),
+  // but the iterator will be invalid. The map needs to exist, otherwise we have
+  // a stale map_id in the database.
+  if (!ConsistencyCheck(it->Valid()))
     return false;
   if (!DatabaseErrorCheck(it->status().ok()))
     return false;
@@ -518,7 +547,7 @@ bool SessionStorageDatabase::DecreaseMapRefCount(const std::string& map_id,
 bool SessionStorageDatabase::ClearMap(const std::string& map_id,
                                       leveldb::WriteBatch* batch) {
   ValuesMap values;
-  if (!ReadMap(map_id, &values, true))
+  if (!ReadMap(map_id, leveldb::ReadOptions(), &values, true))
     return false;
   for (ValuesMap::const_iterator it = values.begin(); it != values.end(); ++it)
     batch->Delete(MapKey(map_id, UTF16ToUTF8(it->first)));
@@ -549,7 +578,7 @@ bool SessionStorageDatabase::DeepCopyArea(
   // Read the values from the old map here. If we don't need to copy the data,
   // this can stay empty.
   ValuesMap values;
-  if (copy_data && !ReadMap(*map_id, &values, false))
+  if (copy_data && !ReadMap(*map_id, leveldb::ReadOptions(), &values, false))
     return false;
   if (!DecreaseMapRefCount(*map_id, 1, batch))
     return false;
diff --git a/webkit/dom_storage/session_storage_database.h b/webkit/dom_storage/session_storage_database.h
index 51f88d7..8eab8e7 100644
--- a/webkit/dom_storage/session_storage_database.h
+++ b/webkit/dom_storage/session_storage_database.h
@@ -19,6 +19,7 @@ class GURL;
 
 namespace leveldb {
 class DB;
+struct ReadOptions;
 class WriteBatch;
 }  // namespace leveldb
 
@@ -27,6 +28,9 @@ namespace dom_storage {
 // SessionStorageDatabase holds the data from multiple namespaces and multiple
 // origins. All DomStorageAreas for session storage share the same
 // SessionStorageDatabase.
+
+// Only one thread is allowed to call the public functions other than
+// ReadAreaValues. Other threads area allowed to call ReadAreaValues.
 class SessionStorageDatabase :
     public base::RefCountedThreadSafe<SessionStorageDatabase> {
  public:
@@ -65,6 +69,10 @@ class SessionStorageDatabase :
   // Reads all namespace IDs from the database.
   bool ReadNamespaceIds(std::vector<std::string>* namespace_ids);
 
+  // Reads all origins which have data stored in |namespace_id|.
+  bool ReadOriginsInNamespace(const std::string& namespace_id,
+                              std::vector<GURL>* origins);
+
  private:
   friend class base::RefCountedThreadSafe<SessionStorageDatabase>;
   friend class SessionStorageDatabaseTest;
@@ -125,6 +133,7 @@ class SessionStorageDatabase :
   // the map doesn't exist.
   bool GetMapForArea(const std::string& namespace_id,
                      const std::string& origin,
+                     const leveldb::ReadOptions& options,
                      bool* exists,
                      std::string* map_id);
 
@@ -140,6 +149,7 @@ class SessionStorageDatabase :
   // true, only keys are aread from the database and the values in |result| will
   // be empty.
   bool ReadMap(const std::string& map_id,
+               const leveldb::ReadOptions& options,
                ValuesMap* result,
                bool only_keys);
   // Writes |values| into the map |map_id|.
diff --git a/webkit/dom_storage/session_storage_database_unittest.cc b/webkit/dom_storage/session_storage_database_unittest.cc
index de71a2f..5796b1c 100644
--- a/webkit/dom_storage/session_storage_database_unittest.cc
+++ b/webkit/dom_storage/session_storage_database_unittest.cc
@@ -52,6 +52,9 @@ class SessionStorageDatabaseTest : public testing::Test {
   void CompareValuesMaps(const ValuesMap& map1, const ValuesMap& map2) const;
   void CheckNamespaceIds(
       const std::set<std::string>& expected_namespace_ids) const;
+  void CheckOrigins(
+      const std::string& namespace_id,
+      const std::set<GURL>& expected_origins) const;
   std::string GetMapForArea(const std::string& namespace_id,
                             const GURL& origin) const;
   int64 GetMapRefCount(const std::string& map_id) const;
@@ -335,18 +338,29 @@ void SessionStorageDatabaseTest::CheckNamespaceIds(
   EXPECT_EQ(expected_namespace_ids.size(), namespace_ids.size());
   for (std::vector<std::string>::const_iterator it = namespace_ids.begin();
        it != namespace_ids.end(); ++it) {
-    LOG(WARNING) << *it;
     EXPECT_TRUE(expected_namespace_ids.find(*it) !=
                 expected_namespace_ids.end());
   }
 }
 
+void SessionStorageDatabaseTest::CheckOrigins(
+    const std::string& namespace_id,
+    const std::set<GURL>& expected_origins) const {
+  std::vector<GURL> origins;
+  EXPECT_TRUE(db_->ReadOriginsInNamespace(namespace_id, &origins));
+  EXPECT_EQ(expected_origins.size(), origins.size());
+  for (std::vector<GURL>::const_iterator it = origins.begin();
+       it != origins.end(); ++it) {
+    EXPECT_TRUE(expected_origins.find(*it) != expected_origins.end());
+  }
+}
+
 std::string SessionStorageDatabaseTest::GetMapForArea(
     const std::string& namespace_id, const GURL& origin) const {
   bool exists;
   std::string map_id;
   EXPECT_TRUE(db_->GetMapForArea(namespace_id, origin.spec(),
-                                 &exists, &map_id));
+                                 leveldb::ReadOptions(), &exists, &map_id));
   EXPECT_TRUE(exists);
   return map_id;
 }
@@ -724,4 +738,37 @@ TEST_F(SessionStorageDatabaseTest, ReadNamespaceIds) {
   CheckDatabaseConsistency();
 }
 
+TEST_F(SessionStorageDatabaseTest, ReadNamespaceIdsInEmptyDatabase) {
+  std::set<std::string> expected_namespace_ids;
+  CheckNamespaceIds(expected_namespace_ids);
+}
+
+TEST_F(SessionStorageDatabaseTest, ReadOriginsInNamespace) {
+  ValuesMap data1;
+  data1[kKey1] = kValue1;
+  data1[kKey2] = kValue2;
+  data1[kKey3] = kValue3;
+
+  std::set<GURL> expected_origins1;
+  ASSERT_TRUE(db_->CommitAreaChanges(kNamespace1, kOrigin1, false, data1));
+  ASSERT_TRUE(db_->CommitAreaChanges(kNamespace1, kOrigin2, false, data1));
+  expected_origins1.insert(kOrigin1);
+  expected_origins1.insert(kOrigin2);
+  CheckOrigins(kNamespace1, expected_origins1);
+
+  std::set<GURL> expected_origins2;
+  ASSERT_TRUE(db_->CommitAreaChanges(kNamespace2, kOrigin2, false, data1));
+  expected_origins2.insert(kOrigin2);
+  CheckOrigins(kNamespace2, expected_origins2);
+
+  ASSERT_TRUE(db_->CloneNamespace(kNamespace1, kNamespaceClone));
+  CheckOrigins(kNamespaceClone, expected_origins1);
+
+  ASSERT_TRUE(db_->DeleteArea(kNamespace1, kOrigin2));
+  expected_origins1.erase(kOrigin2);
+  CheckOrigins(kNamespace1, expected_origins1);
+
+  CheckDatabaseConsistency();
+}
+
 }  // namespace dom_storage