Oilpan: DatabaseThread::m_thread should not get destructed during sweeping

Source/modules/webdatabase/DatabaseThread.cpp

Index: Source/modules/webdatabase/DatabaseThread.cpp
diff --git a/Source/modules/webdatabase/DatabaseThread.cpp b/Source/modules/webdatabase/DatabaseThread.cpp
index 92bd6faaafd082a2364a2d812cd30e194366c29b..b2ac7e7b90822e8e09cab3401deba9a9b62805c9 100644
--- a/Source/modules/webdatabase/DatabaseThread.cpp
+++ b/Source/modules/webdatabase/DatabaseThread.cpp
@@ -43,7 +43,6 @@ namespace blink {
 DatabaseThread::DatabaseThread()
     : m_transactionClient(adoptPtr(new SQLTransactionClient()))
     , m_transactionCoordinator(adoptPtrWillBeNoop(new SQLTransactionCoordinator()))
-    , m_cleanupSync(0)
     , m_terminationRequested(false)
 {
 }
@@ -51,13 +50,7 @@ DatabaseThread::DatabaseThread()
 DatabaseThread::~DatabaseThread()
 {
     ASSERT(m_openDatabaseSet.isEmpty());
-    // Oilpan: The database thread must have finished its cleanup tasks before
-    // the following clear(). Otherwise, WebThread destructor blocks the caller
-    // thread, and causes a deadlock with ThreadState cleanup.
-    // DatabaseContext::stop() asks the database thread to close all of
-    // databases, and wait until GC heap cleanup of the database thread. So we
-    // can safely destruct WebThread here.
-    m_thread.clear();
+    ASSERT(!m_thread);
 }
 
 void DatabaseThread::trace(Visitor* visitor)
@@ -81,14 +74,15 @@ void DatabaseThread::setupDatabaseThread()
     m_thread->attachGC();
 }
 
-void DatabaseThread::requestTermination(TaskSynchronizer *cleanupSync)
+void DatabaseThread::terminate()
 {
     MutexLocker lock(m_terminationRequestedMutex);

[Mads Ager (chromium), 2014/09/23 13:44:37]

I think we should limit the scope of this lock so it is only held while updating
terminationRequested and posting the task. We don't want to hold the lock while
waiting for the thread to terminate.

{
    MutexLocker lock(...);
    ...
    m_thread->postTask(...);
}
m_thread->clear();

?

     ASSERT(!m_terminationRequested);
     m_terminationRequested = true;
-    m_cleanupSync = cleanupSync;
     WTF_LOG(StorageAPI, "DatabaseThread %p was asked to terminate\n", this);
     m_thread->postTask(new Task(WTF::bind(&DatabaseThread::cleanupDatabaseThread, this)));
+    // The WebThread destructor blocks until the database thread processes the cleanup task.
+    m_thread.clear();
 }
 
 bool DatabaseThread::terminationRequested(TaskSynchronizer* taskSynchronizer) const
@@ -126,8 +120,6 @@ void DatabaseThread::cleanupDatabaseThread()
 void DatabaseThread::cleanupDatabaseThreadCompleted()
 {
     m_thread->detachGC();
-    if (m_cleanupSync) // Someone wanted to know when we were done cleaning up.
-        m_cleanupSync->taskCompleted();
 }
 
 void DatabaseThread::recordDatabaseOpen(DatabaseBackend* database)