Source/modules/webdatabase/DatabaseContext.cpp

/*
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 * Copyright (C) 2011 Google, Inc. All Rights Reserved.
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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#include "config.h"
#include "modules/webdatabase/DatabaseContext.h"

#include "core/dom/Document.h"
#include "core/dom/ExecutionContext.h"
#include "core/page/Chrome.h"
#include "core/page/ChromeClient.h"
#include "core/page/Page.h"
#include "core/page/Settings.h"
#include "modules/webdatabase/Database.h"
#include "modules/webdatabase/DatabaseManager.h"
#include "modules/webdatabase/DatabaseTask.h"
#include "modules/webdatabase/DatabaseThread.h"
#include "platform/weborigin/SchemeRegistry.h"
#include "platform/weborigin/SecurityOrigin.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. ExecutionContext
// 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 ref(). This lets DatabaseContext keep itself alive.
// Note that paired deref() is called from contextDestroyed().
//
// Once a DatabaseContext is associated with a ExecutionContext, it will
// live until after the ExecutionContext 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 ExecutionContext, the Database
// will re-use the same DatabaseContext.
//
// At Shutdown:
// ===========
// During shutdown, the DatabaseContext needs to:
// 1. "outlive" the ExecutionContext.
//    - This is needed because the DatabaseContext needs to remove itself from the
//      ExecutionContext's ActiveDOMObject list and ContextLifecycleObserver
//      list. This removal needs to be executed on the script's thread. Hence, we
//      rely on the ExecutionContext'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 ExecutionContext 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 ExecutionContext or the Databases
// destruct first.
//
// The RefPtrs in the Databases and ExecutionContext will ensure that the
// DatabaseContext will outlive both regardless of which of the 2 destructs first.

PassRefPtr<DatabaseContext> DatabaseContext::create(ExecutionContext* context)
{
    RefPtr<DatabaseContext> self = adoptRef(new DatabaseContext(context));
    self->ref(); // Is deref()-ed on contextDestroyed().
    return self.release();
}

DatabaseContext::DatabaseContext(ExecutionContext* context)
    : ActiveDOMObject(context)
    , m_hasOpenDatabases(false)
    , m_isRegistered(true) // will register on construction below.
    , m_hasRequestedTermination(false)
{
    // ActiveDOMObject expects this to be called to set internal flags.
    suspendIfNeeded();

    // For debug accounting only. We must do this before we register the
    // instance. The assertions assume this.
    DatabaseManager::manager().didConstructDatabaseContext();

    DatabaseManager::manager().registerDatabaseContext(this);
}

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

    // For debug accounting only. We must call this last. The assertions assume
    // this.
    DatabaseManager::manager().didDestructDatabaseContext();
}

// This is called if the associated ExecutionContext is destructing 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 shutdown naturally
// because the database closing process may still make use of this context.
// It is not safe to just delete the context here.
void DatabaseContext::contextDestroyed()
{
    stopDatabases();
    ActiveDOMObject::contextDestroyed();
    deref(); // paired with the ref() call on create().
}

// 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();
}

PassRefPtr<DatabaseContext> DatabaseContext::backend()
{
    DatabaseContext* backend = static_cast<DatabaseContext*>(this);
    return backend;
}

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* cleanupSync)
{
    if (m_isRegistered) {
        DatabaseManager::manager().unregisterDatabaseContext(this);
        m_isRegistered = false;
    }

    // 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.

    if (m_databaseThread && !m_hasRequestedTermination) {
        m_databaseThread->requestTermination(cleanupSync);
        m_hasRequestedTermination = true;
        return true;
    }
    return false;
}

bool DatabaseContext::allowDatabaseAccess() const
{
    if (executionContext()->isDocument()) {
        Document* document = toDocument(executionContext());
        return document->page();
    }
    ASSERT(executionContext()->isWorkerGlobalScope());
    // allowDatabaseAccess is not yet implemented for workers.
    return true;
}

SecurityOrigin* DatabaseContext::securityOrigin() const
{
    return executionContext()->securityOrigin();
}

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

} // namespace WebCore