blob: 33ba17f934b6f99142cf39079a31a6af781818a8 [file] [log] [blame]
// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "third_party/blink/renderer/bindings/core/v8/active_script_wrappable.h"
#include "third_party/blink/renderer/bindings/core/v8/script_promise_resolver.h"
#include "third_party/blink/renderer/core/core_export.h"
#include "third_party/blink/renderer/platform/bindings/script_wrappable.h"
#include "third_party/blink/renderer/platform/wtf/compiler.h"
namespace blink {
class DisplayLockSuspendedHandle;
class Element;
class V8DisplayLockCallback;
class DisplayLockScopedLogger;
class CORE_EXPORT DisplayLockContext final
: public ScriptWrappable,
public ActiveScriptWrappable<DisplayLockContext>,
public ContextLifecycleObserver {
USING_PRE_FINALIZER(DisplayLockContext, Dispose);
// Conceptually the states are private, but made public for debugging /
// logging.
enum State {
enum LifecycleUpdateState {
DisplayLockContext(Element*, ExecutionContext*);
~DisplayLockContext() override;
// GC functions.
void Trace(blink::Visitor*) override;
void Dispose();
// ContextLifecycleObserver overrides.
void ContextDestroyed(ExecutionContext*) override;
// ActiveScriptWrappable overrides. If there is an outstanding task scheduled
// to process the callback queue, then this return true.
// TODO(vmpstr): In the future this would also be true while we're doing
// co-operative work.
bool HasPendingActivity() const final;
// Notify that the lock was requested. Note that for a new context, this has
// to be called first. For an existing lock, this will either extend the
// lifetime of the current lock, or start acquiring a new lock (depending on
// whether this lock is active or passive).
void RequestLock(V8DisplayLockCallback*, ScriptState*);
// Returns true if the promise associated with this context was already
// resolved (or rejected).
bool IsResolved() const { return state_ == kResolved; }
// Returns a ScriptPromise associated with this context.
ScriptPromise Promise() const {
return resolver_->Promise();
// Called when the connected state may have changed.
void NotifyConnectedMayHaveChanged();
// Rejects the associated promise if one exists, and clears the current queue.
// This effectively makes the context finalized.
void RejectAndCleanUp();
// JavaScript interface implementation.
void schedule(V8DisplayLockCallback*);
DisplayLockSuspendedHandle* suspend();
Element* lockedElement() const;
// Lifecycle observation / state functions.
bool ShouldStyle() const;
void DidStyle();
bool ShouldLayout() const;
void DidLayout();
bool ShouldPrePaint() const;
void DidPrePaint();
bool ShouldPaint() const;
void DidPaint();
void DidAttachLayoutTree();
friend class DisplayLockContextTest;
friend class DisplayLockSuspendedHandle;
// Schedules a new callback. If this is the first callback to be scheduled,
// then a valid ScriptState must be provided, which will be used to create a
// new ScriptPromiseResolver. In other cases, the ScriptState is ignored.
void ScheduleCallback(V8DisplayLockCallback*);
// Processes the current queue of callbacks.
void ProcessQueue();
// Called by the suspended handle in order to resume context operations.
void Resume();
// Called by the suspended handle informing us that it was disposed without
// resuming, meaning it will never resume.
void NotifyWillNotResume();
// Schedule a task if one is required. Specifically, this would schedule a
// task if one was not already scheduled and if we need to either process
// callbacks or to resolve the associated promise.
void ScheduleTaskIfNeeded();
// A function that finishes resolving the promise by establishing a microtask
// checkpoint. Note that this should be scheduled after entering the
// kResolving state. If the state is still kResolving after the microtask
// checkpoint finishes (ie, the lock was not re-acquired), we enter the final
// kResolved state.
void FinishResolution();
// Initiate a commit.
void StartCommit();
// The following functions propagate dirty bits from the locked element up to
// the ancestors in order to be reached. They return true if the element or
// its subtree were dirty, and false otherwise.
bool MarkAncestorsForStyleRecalcIfNeeded();
bool MarkAncestorsForLayoutIfNeeded();
// Marks the display lock as being disconnected. Note that this removes the
// strong reference to the element in case the element is deleted. Once we're
// disconnected, there are will be no calls to the context until we reconnect,
// so we should allow for the element to get GCed meanwhile.
void MarkAsDisconnected();
// Returns the element asserting that it exists.
ALWAYS_INLINE Element* GetElement() const {
return weak_element_handle_;
HeapVector<Member<V8DisplayLockCallback>> callbacks_;
Member<ScriptPromiseResolver> resolver_;
// Note that we hold both a weak and a strong reference to the element. The
// strong reference is sometimes set to nullptr, meaning that we can GC it if
// nothing else is holding a strong reference. We use weak_element_handle_ to
// detect such a case so that we don't also keep the context alive needlessly.
// We need a strong reference, since the element can be accessed from script
// via this context. Specifically DisplayLockContext::lockedElement() returns
// the element to script. This means that callbacks pending in the context can
// actually append the element to the tree. This means a strong reference is
// needed to prevent GC from destroying the element.
// However, once we're in kDisconnected state, it means that we have no
// callbacks pending and we haven't been connected to the DOM tree. It's also
// possible that the script has lost the reference to the locked element. This
// means the element should be GCed, so we need to let go of the strong
// reference. If we don't, we can cause a leak of an element and a display
// lock context.
// In case the script did not lose the element handle and will connect it in
// the future, we do retain a weak handle. We also use the weak handle to
// check if the element was destroyed for the purposes of allowing this
// context to be GCed as well.
Member<Element> element_;
WeakMember<Element> weak_element_handle_;
bool process_queue_task_scheduled_ = false;
unsigned suspended_count_ = 0;
State state_ = kUninitialized;
LifecycleUpdateState lifecycle_update_state_ = kNeedsStyle;
} // namespace blink