Revert of DatabaseBackend objects should be destructed in the originator...

Revert of DatabaseBackend objects should be destructed in the originator thread (https://codereview.chromium.org/183883005/)

Reason for revert:
Unnecessary change


Original issue's description:
> DatabaseBackend objects should be destructed in the originator thread.
> 
> Before this CL, it was possible that DatabaseThread held the last
> references of DatabaseBackend objects and it was released in the
> database thread.
> We must destruct objects in the originator thread in Oilpan.
> 
> Implementation:
> DatabaseThread::recordDatabaseClosed doesn't remove a RefPtr<
> DatabaseBackend>, and we release RefPtr<DatabaseBackend> objects
> in ~DatabaseThread, which is executed in the main/worker thread.
> Note that there are no ways to close a database explicitly, and
> DatabaseBackend objects are never destructed before their
> DatabaseContext is stopped. DatabaseThread::recordDatabaseClosed
> is actually unnecessary.
> 
> DatabaseThread doesn't know DatabaseBackend open status any longer.
> We remove DatabaseThread::isDatabaseOpen, and its existing
> callsites use DatabaseBackend::open() instead.
> 
> 
> BUG=347902
> TEST=none; no visible behavior changes hopefully.
> R=michaeln@chromium.org
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168362

TBR=michaeln@chromium.org,oilpan-reviews@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=347902

Review URL: https://codereview.chromium.org/178103007

git-svn-id: svn://svn.chromium.org/blink/trunk@168431 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/modules/webdatabase/DatabaseTask.cpp

@@ -82,7 +82,7 @@ void DatabaseTask::run()
     ASSERT(!m_complete);
 #endif
 
-    if (!m_synchronizer && !m_database->opened()) {
+    if (!m_synchronizer && !m_database->databaseContext()->databaseThread()->isDatabaseOpen(m_database.get())) {
         taskCancelled();
 #if !LOG_DISABLED
         m_complete = true;

third_party/WebKit/Source/modules/webdatabase/DatabaseThread.cpp

@@ -48,8 +48,6 @@ DatabaseThread::DatabaseThread()
 
 DatabaseThread::~DatabaseThread()
 {
-    ASSERT(m_thread);
-    ASSERT(!isDatabaseThread());
     bool terminationRequested;
     {
         MutexLocker lock(m_terminationRequestedMutex);
@@ -98,8 +96,11 @@ void DatabaseThread::cleanupDatabaseThread()
     // Close the databases that we ran transactions on. This ensures that if any transactions are still open, they are rolled back and we don't leave the database in an
     // inconsistent or locked state.
     if (m_openDatabaseSet.size() > 0) {
-        DatabaseSet::iterator end = m_openDatabaseSet.end();
-        for (DatabaseSet::iterator it = m_openDatabaseSet.begin(); it != end; ++it)
+        // As the call to close will modify the original set, we must take a copy to iterate over.
+        DatabaseSet openSetCopy;
+        openSetCopy.swap(m_openDatabaseSet);
+        DatabaseSet::iterator end = openSetCopy.end();
+        for (DatabaseSet::iterator it = openSetCopy.begin(); it != end; ++it)
             (*it).get()->close();
     }
 
@@ -121,9 +122,17 @@ void DatabaseThread::recordDatabaseClosed(DatabaseBackend* database)
     MutexLocker lock(m_terminationRequestedMutex);
 #endif
     ASSERT(isDatabaseThread());
-    ASSERT_UNUSED(database, database);
+    ASSERT(database);
     ASSERT(m_terminationRequested || m_openDatabaseSet.contains(database));
-    // We'll clear m_openDatabaseSet in the destructor.
+    m_openDatabaseSet.remove(database);
+}
+
+bool DatabaseThread::isDatabaseOpen(DatabaseBackend* database)
+{
+    ASSERT(isDatabaseThread());
+    ASSERT(database);
+    MutexLocker lock(m_terminationRequestedMutex);
+    return !m_terminationRequested && m_openDatabaseSet.contains(database);
 }
 
 void DatabaseThread::scheduleTask(PassOwnPtr<DatabaseTask> task)

third_party/WebKit/Source/modules/webdatabase/DatabaseThread.h

@@ -61,6 +61,7 @@ public:
 
     void recordDatabaseOpen(DatabaseBackend*);
     void recordDatabaseClosed(DatabaseBackend*);
+    bool isDatabaseOpen(DatabaseBackend*);
 
     bool isDatabaseThread() { return m_thread && m_thread->isCurrentThread(); }