idb_request_queue_item.h | Explore in Territory

// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef THIRD_PARTY_BLINK_RENDERER_MODULES_INDEXEDDB_IDB_REQUEST_QUEUE_ITEM_H_
#define THIRD_PARTY_BLINK_RENDERER_MODULES_INDEXEDDB_IDB_REQUEST_QUEUE_ITEM_H_

#include <memory>

#include "base/dcheck_is_on.h"
#include "base/functional/callback.h"
#include "base/memory/weak_ptr.h"
#include "mojo/public/cpp/bindings/pending_associated_remote.h"
#include "third_party/blink/public/mojom/indexeddb/indexeddb.mojom-blink.h"
#include "third_party/blink/renderer/platform/heap/persistent.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
#include "third_party/blink/renderer/platform/wtf/deque.h"
#include "third_party/blink/renderer/platform/wtf/vector.h"

namespace blink {

class DOMException;
class IDBDatabaseGetAllResultSinkImpl;
class IDBKey;
class IDBRequest;
class IDBRequestLoader;
class IDBRequestTest;
class IDBValue;

// Queues up a transaction's IDBRequest results for orderly delivery.
//
// The IndexedDB specification requires that the events corresponding to IDB
// request results fire in the order in which the requests were issued. The
// browser-side backend processes requests in order, but the Blink side may need
// to perform post-processing on the results (e.g. large value unwrapping).
// When a result needs post-processing, this queue captures all results received
// during the post-processing steps. The events for these results may only fire
// after the post-processed result's event is fired.
//
// A queue item holds a Persistent (not garbage-collected) reference to the
// IDBRequest whose result it will deliver. This creates a reference cycle,
// because IDBRequest holds a pointer to its IDBTransaction, and IDBTransaction
// stores all pending IDBRequestQueueItem instances for its requests in a queue
// via non-garbage-collected pointers (std::unique_ptr). To avoid leaks, the
// request-processing code must ensure that IDBTransaction's queue gets drained
// at some point, even if the transaction's ExecutionContext goes away. The
// lifecycle tests in IDBTransactionTest aim to cover this requirement.
//
// Given that the cycle above exists, the closures passed to IDBRequestQueueItem
// can safely store Persistent pointers the IDBRequest or to the IDBTransaction.
class MODULES_EXPORT IDBRequestQueueItem { … };

IDBRequestQueue;

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_MODULES_INDEXEDDB_IDB_REQUEST_QUEUE_ITEM_H_
chromium/third_party/blink/renderer/modules/indexeddb/idb_request_queue_item.h
