modules/webdatabase/database_context.cc

/*
 * Copyright (C) 2008 Apple Inc. All Rights Reserved.
 * Copyright (C) 2011 Google, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
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 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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#include "third_party/blink/renderer/modules/webdatabase/database_context.h"

#include "third_party/blink/renderer/core/dom/document.h"
#include "third_party/blink/renderer/core/execution_context/execution_context.h"
#include "third_party/blink/renderer/modules/webdatabase/database.h"
#include "third_party/blink/renderer/modules/webdatabase/database_manager.h"
#include "third_party/blink/renderer/modules/webdatabase/database_task.h"
#include "third_party/blink/renderer/modules/webdatabase/database_thread.h"
#include "third_party/blink/renderer/platform/weborigin/scheme_registry.h"
#include "third_party/blink/renderer/platform/weborigin/security_origin.h"
#include "third_party/blink/renderer/platform/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 ExecutionContextLifecycleObserver list and
//      ExecutionContextLifecycleObserver
//      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 = MakeGarbageCollected<DatabaseContext>(context);
  DatabaseManager::Manager().RegisterDatabaseContext(self);
  return self;
}

DatabaseContext::DatabaseContext(ExecutionContext* context)
    : ExecutionContextLifecycleObserver(context),
      has_open_databases_(false),
      has_requested_termination_(false) {
  DCHECK(IsMainThread());

  // 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();
}

void DatabaseContext::Trace(Visitor* visitor) {
  visitor->Trace(database_thread_);
  ExecutionContextLifecycleObserver::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);
}

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

DatabaseThread* DatabaseContext::GetDatabaseThread() {
  if (!database_thread_ && !has_open_databases_) {
    // 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.
    DCHECK(!has_requested_termination_);

    // 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.
    database_thread_ = MakeGarbageCollected<DatabaseThread>();
    database_thread_->Start();
  }

  return database_thread_.Get();
}

bool DatabaseContext::DatabaseThreadAvailable() {
  return GetDatabaseThread() && !has_requested_termination_;
}

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()) {
    has_requested_termination_ = true;
    // This blocks until the database thread finishes the cleanup task.
    database_thread_->Terminate();
  }
}

bool DatabaseContext::AllowDatabaseAccess() const {
  return Document::From(GetExecutionContext())->IsActive();
}

const SecurityOrigin* DatabaseContext::GetSecurityOrigin() const {
  return GetExecutionContext()->GetSecurityOrigin();
}

bool DatabaseContext::IsContextThread() const {
  return GetExecutionContext()->IsContextThread();
}

}  // namespace blink