Source/WebCore/Modules/webdatabase/DatabaseContext.cpp

/*
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 * Copyright (C) 2011 Google, Inc. All Rights Reserved.
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#include "config.h"
#include "DatabaseContext.h"

#include "Chrome.h"
#include "ChromeClient.h"
#include "Database.h"
#include "DatabaseManager.h"
#include "DatabaseTask.h"
#include "DatabaseThread.h"
#include "Document.h"
#include "LegacySchemeRegistry.h"
#include "Page.h"
#include "ScriptExecutionContext.h"
#include "SecurityOrigin.h"
#include "SecurityOriginData.h"

namespace WebCore {

// How the DatabaseContext Life-Cycle works?
// ========================================
// ... in other words, who's keeping the DatabaseContext alive and how long does
// it need to stay alive?
//
// The DatabaseContext is referenced from RefPtrs in:
// 1. ScriptExecutionContext
// 2. Database
//
// At Birth:
// ========
// We create a DatabaseContext only when there is a need i.e. the script tries to
// open a Database via DatabaseManager::openDatabase().
//
// The DatabaseContext constructor will call setDatabaseContext() on the
// the ScriptExecutionContext. This sets the RefPtr in the ScriptExecutionContext
// for keeping the DatabaseContext alive. Since the DatabaseContext is only
// created from the script thread, it is safe for the constructor to call
// ScriptExecutionContext::setDatabaseContext().
//
// Once a DatabaseContext is associated with a ScriptExecutionContext, it will
// live until after the ScriptExecutionContext destructs. This is true even if
// we don't succeed in opening any Databases for that context. When we do
// succeed in opening Databases for this ScriptExecutionContext, the Database
// will re-use the same DatabaseContext.
//
// At Shutdown:
// ===========
// During shutdown, the DatabaseContext needs to:
// 1. "outlive" the ScriptExecutionContext.
//    - This is needed because the DatabaseContext needs to remove itself from the
//      ScriptExecutionContext's ActiveDOMObject list and ContextDestructionObserver
//      list. This removal needs to be executed on the script's thread. Hence, we
//      rely on the ScriptExecutionContext's shutdown process to call
//      stop() and contextDestroyed() to give us a chance to clean these up from
//      the script thread.
//
// 2. "outlive" the Databases.
//    - This is because they may make use of the DatabaseContext to execute a close
//      task and shutdown in an orderly manner. When the Databases are destructed,
//      they will deref the DatabaseContext from the DatabaseThread.
//
// During shutdown, the ScriptExecutionContext is shutting down on the script thread
// while the Databases are shutting down on the DatabaseThread. Hence, there can be
// a race condition as to whether the ScriptExecutionContext or the Databases
// destruct first.
//
// The RefPtrs in the Databases and ScriptExecutionContext will ensure that the
// DatabaseContext will outlive both regardless of which of the 2 destructs first.


DatabaseContext::DatabaseContext(Document& document)
    : ActiveDOMObject(document)
{
    ASSERT(!document.databaseContext());
    document.setDatabaseContext(this);
}

DatabaseContext::~DatabaseContext()
{
    stopDatabases();
    ASSERT(!m_databaseThread || m_databaseThread->terminationRequested());
    ASSERT(!scriptExecutionContext() || !scriptExecutionContext()->databaseContext());
}

// This is called if the associated ScriptExecutionContext is destroyed while
// we're still associated with it. That's our cue to disassociate and shutdown.
// To do this, we stop the database and let everything shut down naturally
// because the database closing process might still make use of this context.
// It is not safe to just delete the context here.
void DatabaseContext::contextDestroyed()
{
    ActiveDOMObject::contextDestroyed();
    stopDatabases();
}

// stop() is from stopActiveDOMObjects() which indicates that the owner Frame
// or WorkerThread is shutting down. Initiate the orderly shutdown by stopping
// the associated databases.
void DatabaseContext::stop()
{
    stopDatabases();
}

DatabaseThread* DatabaseContext::databaseThread()
{
    if (!m_databaseThread && !m_hasOpenDatabases) {
        // It's OK to ask for the m_databaseThread after we've requested
        // termination because we're still using it to execute the closing
        // of the database. However, it is NOT OK to create a new thread
        // after we've requested termination.
        ASSERT(!m_hasRequestedTermination);

        // Create the database thread on first request - but not if at least one database was already opened,
        // because in that case we already had a database thread and terminated it and should not create another.
        m_databaseThread = DatabaseThread::create();
        m_databaseThread->start();
    }

    return m_databaseThread.get();
}

bool DatabaseContext::stopDatabases(DatabaseTaskSynchronizer* synchronizer)
{
    // FIXME: What guarantees this is never called after the script execution context is null?
    ASSERT(scriptExecutionContext());

    // Though we initiate termination of the DatabaseThread here in
    // stopDatabases(), we can't clear the m_databaseThread ref till we get to
    // the destructor. This is because the Databases that are managed by
    // DatabaseThread still rely on this ref between the context and the thread
    // to execute the task for closing the database. By the time we get to the
    // destructor, we're guaranteed that the databases are destructed (which is
    // why our ref count is 0 then and we're destructing). Then, the
    // m_databaseThread RefPtr destructor will deref and delete the
    // DatabaseThread.
    bool result = m_databaseThread && !m_hasRequestedTermination;
    if (result) {
        m_databaseThread->requestTermination(synchronizer);
        m_hasRequestedTermination = true;
    }

    auto& context = *scriptExecutionContext();
    if (context.databaseContext()) {
        ASSERT(context.databaseContext() == this);
        context.setDatabaseContext(nullptr);
    }

    return result;
}

bool DatabaseContext::allowDatabaseAccess() const
{
    auto* context = scriptExecutionContext();
    if (is<Document>(*context)) {
        auto& document = downcast<Document>(*context);
        if (!document.page() || (document.page()->usesEphemeralSession() && !LegacySchemeRegistry::allowsDatabaseAccessInPrivateBrowsing(document.securityOrigin().protocol())))
            return false;
        return true;
    }
    ASSERT(context->isWorkerGlobalScope());
    // allowDatabaseAccess is not yet implemented for workers.
    return true;
}

void DatabaseContext::databaseExceededQuota(const String& name, DatabaseDetails details)
{
    auto* context = scriptExecutionContext();
    if (is<Document>(*context)) {
        auto& document = downcast<Document>(*context);
        if (Page* page = document.page())
            page->chrome().client().exceededDatabaseQuota(*document.frame(), name, details);
        return;
    }
    ASSERT(context->isWorkerGlobalScope());
}

const SecurityOriginData& DatabaseContext::securityOrigin() const
{
    return scriptExecutionContext()->securityOrigin()->data();
}

bool DatabaseContext::isContextThread() const
{
    return scriptExecutionContext()->isContextThread();
}

} // namespace WebCore