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

/*
 * Copyright (C) 2008 Apple Inc. All Rights Reserved.
 * Copyright (C) 2011 Google, Inc. All Rights Reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *    documentation and/or other materials provided with the distribution.
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 * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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#include "modules/webdatabase/DatabaseContext.h"

#include "core/dom/Document.h"
#include "core/dom/ExecutionContext.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"
#include "wtf/Assertions.h"

namespace blink {

// 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:
// 1. DatabaseManager
// 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 register itself to DatabaseManager. This
// lets DatabaseContext keep itself alive until it is unregisterd in
// 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 release the DatabaseContext reference 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 Members in the Databases and DatabaseManager will ensure that the
// DatabaseContext will outlive Database and ExecutionContext regardless of
// which of the 2 destructs first.

DatabaseContext* DatabaseContext::create(ExecutionContext* context) {
  DatabaseContext* self = new DatabaseContext(context);
  DatabaseManager::manager().registerDatabaseContext(self);
  return self;
}

DatabaseContext::DatabaseContext(ExecutionContext* context)
    : ActiveDOMObject(context),
      m_hasOpenDatabases(false),
      m_hasRequestedTermination(false) {
  DCHECK(isMainThread());

  // 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();
}

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

DEFINE_TRACE(DatabaseContext) {
  visitor->trace(m_databaseThread);
  ActiveDOMObject::trace(visitor);
}

// 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();
  DatabaseManager::manager().unregisterDatabaseContext(this);
  ActiveDOMObject::contextDestroyed();
}

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

DatabaseContext* DatabaseContext::backend() {
  return this;
}

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::databaseThreadAvailable() {
  return databaseThread() && !m_hasRequestedTermination;
}

void DatabaseContext::stopDatabases() {
  // 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 (databaseThreadAvailable()) {
    m_hasRequestedTermination = true;
    // This blocks until the database thread finishes the cleanup task.
    m_databaseThread->terminate();
  }
}

bool DatabaseContext::allowDatabaseAccess() const {
  return toDocument(getExecutionContext())->isActive();
}

SecurityOrigin* DatabaseContext::getSecurityOrigin() const {
  return getExecutionContext()->getSecurityOrigin();
}

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

}  // namespace blink