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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#ifndef mozilla_CycleCollectedJSContext_h
#define mozilla_CycleCollectedJSContext_h
#include <queue>
#include "mozilla/Attributes.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/dom/AtomList.h"
#include "mozilla/dom/Promise.h"
#include "js/GCVector.h"
#include "js/Promise.h"
#include "nsCOMPtr.h"
#include "nsRefPtrHashtable.h"
#include "nsTArray.h"
class nsCycleCollectionNoteRootCallback;
class nsIRunnable;
class nsThread;
namespace mozilla {
class AutoSlowOperation;
class CycleCollectedJSContext;
class CycleCollectedJSRuntime;
namespace dom {
class Exception;
class WorkerJSContext;
class WorkletJSContext;
} // namespace dom
// Contains various stats about the cycle collection.
struct CycleCollectorResults {
CycleCollectorResults() {
// Initialize here so when we increment mNumSlices the first time we're
// not using uninitialized memory.
void Init() {
mForcedGC = false;
mMergedZones = false;
mAnyManual = false;
mVisitedRefCounted = 0;
mVisitedGCed = 0;
mFreedRefCounted = 0;
mFreedGCed = 0;
mFreedJSZones = 0;
mNumSlices = 1;
// mNumSlices is initialized to one, because we call Init() after the
// per-slice increment of mNumSlices has already occurred.
bool mForcedGC;
bool mMergedZones;
// mAnyManual is true if any slice was manually triggered, and at shutdown.
bool mAnyManual;
uint32_t mVisitedRefCounted;
uint32_t mVisitedGCed;
uint32_t mFreedRefCounted;
uint32_t mFreedGCed;
uint32_t mFreedJSZones;
uint32_t mNumSlices;
class MicroTaskRunnable {
MicroTaskRunnable() = default;
MOZ_CAN_RUN_SCRIPT virtual void Run(AutoSlowOperation& aAso) = 0;
virtual bool Suppressed() { return false; }
virtual ~MicroTaskRunnable() = default;
// Support for JS FinalizationRegistry objects, which allow a JS callback to be
// registered that is called when objects die.
// We keep a vector of functions that call back into the JS engine along
// with their associated incumbent globals, one per FinalizationRegistry object
// that has pending cleanup work. These are run in their own task.
class FinalizationRegistryCleanup {
explicit FinalizationRegistryCleanup(CycleCollectedJSContext* aContext);
void Init();
void Destroy();
void QueueCallback(JSFunction* aDoCleanup, JSObject* aIncumbentGlobal);
MOZ_CAN_RUN_SCRIPT void DoCleanup();
static void QueueCallback(JSFunction* aDoCleanup, JSObject* aIncumbentGlobal,
void* aData);
class CleanupRunnable;
struct Callback {
JSFunction* mCallbackFunction;
JSObject* mIncumbentGlobal;
void trace(JSTracer* trc);
// This object is part of CycleCollectedJSContext, so it's safe to have a raw
// pointer to its containing context here.
CycleCollectedJSContext* mContext;
using CallbackVector = JS::GCVector<Callback, 0, InfallibleAllocPolicy>;
JS::PersistentRooted<CallbackVector> mCallbacks;
class CycleCollectedJSContext : dom::PerThreadAtomCache, private JS::JobQueue {
friend class CycleCollectedJSRuntime;
virtual ~CycleCollectedJSContext();
nsresult Initialize(JSRuntime* aParentRuntime, uint32_t aMaxBytes);
virtual CycleCollectedJSRuntime* CreateRuntime(JSContext* aCx) = 0;
size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
static JSObject* GetIncumbentGlobalCallback(JSContext* aCx);
static bool EnqueuePromiseJobCallback(JSContext* aCx,
JS::HandleObject aPromise,
JS::HandleObject aJob,
JS::HandleObject aAllocationSite,
JS::HandleObject aIncumbentGlobal,
void* aData);
static void PromiseRejectionTrackerCallback(
JSContext* aCx, bool aMutedErrors, JS::HandleObject aPromise,
JS::PromiseRejectionHandlingState state, void* aData);
void AfterProcessMicrotasks();
void ProcessStableStateQueue();
void CleanupIDBTransactions(uint32_t aRecursionDepth);
enum DeferredFinalizeType {
virtual dom::WorkerJSContext* GetAsWorkerJSContext() { return nullptr; }
virtual dom::WorkletJSContext* GetAsWorkletJSContext() { return nullptr; }
CycleCollectedJSRuntime* Runtime() const {
return mRuntime;
already_AddRefed<dom::Exception> GetPendingException() const;
void SetPendingException(dom::Exception* aException);
std::queue<RefPtr<MicroTaskRunnable>>& GetMicroTaskQueue();
std::queue<RefPtr<MicroTaskRunnable>>& GetDebuggerMicroTaskQueue();
JSContext* Context() const {
return mJSContext;
JS::RootingContext* RootingCx() const {
return JS::RootingContext::get(mJSContext);
void SetTargetedMicroTaskRecursionDepth(uint32_t aDepth) {
mTargetedMicroTaskRecursionDepth = aDepth;
JSContext* MaybeContext() const { return mJSContext; }
// nsThread entrypoints
// MOZ_CAN_RUN_SCRIPT_BOUNDARY so we don't need to annotate
// nsThread::ProcessNextEvent and all its callers MOZ_CAN_RUN_SCRIPT for now.
// But we really should!
virtual void BeforeProcessTask(bool aMightBlock);
// MOZ_CAN_RUN_SCRIPT_BOUNDARY so we don't need to annotate
// nsThread::ProcessNextEvent and all its callers MOZ_CAN_RUN_SCRIPT for now.
// But we really should!
virtual void AfterProcessTask(uint32_t aRecursionDepth);
// Check whether we need an idle GC task.
void IsIdleGCTaskNeeded() const;
uint32_t RecursionDepth() const;
// Run in stable state (call through nsContentUtils)
void RunInStableState(already_AddRefed<nsIRunnable>&& aRunnable);
void AddPendingIDBTransaction(already_AddRefed<nsIRunnable>&& aTransaction);
// Get the CycleCollectedJSContext for a JSContext.
// Returns null only if Initialize() has not completed on or during
// destruction of the CycleCollectedJSContext.
static CycleCollectedJSContext* GetFor(JSContext* aCx);
// Get the current thread's CycleCollectedJSContext. Returns null if there
// isn't one.
static CycleCollectedJSContext* Get();
// Queue an async microtask to the current main or worker thread.
virtual void DispatchToMicroTask(
already_AddRefed<MicroTaskRunnable> aRunnable);
// Call EnterMicroTask when you're entering JS execution.
// Usually the best way to do this is to use nsAutoMicroTask.
void EnterMicroTask() { ++mMicroTaskLevel; }
void LeaveMicroTask() {
if (--mMicroTaskLevel == 0) {
bool IsInMicroTask() const { return mMicroTaskLevel != 0; }
uint32_t MicroTaskLevel() const { return mMicroTaskLevel; }
void SetMicroTaskLevel(uint32_t aLevel) { mMicroTaskLevel = aLevel; }
bool PerformMicroTaskCheckPoint(bool aForce = false);
void PerformDebuggerMicroTaskCheckpoint();
bool IsInStableOrMetaStableState() const { return mDoingStableStates; }
// Storage for watching rejected promises waiting for some client to
// consume their rejection.
// Promises in this list have been rejected in the last turn of the
// event loop without the rejection being handled.
// Note that this can contain nullptrs in place of promises removed because
// they're consumed before it'd be reported.
JS::PersistentRooted<JS::GCVector<JSObject*, 0, js::SystemAllocPolicy>>
// Promises in this list have previously been reported as rejected
// (because they were in the above list), but the rejection was handled
// in the last turn of the event loop.
JS::PersistentRooted<JS::GCVector<JSObject*, 0, js::SystemAllocPolicy>>
nsTArray<nsCOMPtr<nsISupports /* UncaughtRejectionObserver */>>
virtual bool IsSystemCaller() const = 0;
// Unused on main thread. Used by AutoJSAPI on Worker and Worklet threads.
virtual void ReportError(JSErrorReport* aReport,
JS::ConstUTF8CharsZ aToStringResult) {
// JS::JobQueue implementation: see js/public/Promise.h.
// SpiderMonkey uses some of these methods to enqueue promise resolution jobs.
// Others protect the debuggee microtask queue from the debugger's
// interruptions; see the comments on JS::AutoDebuggerJobQueueInterruption for
// details.
JSObject* getIncumbentGlobal(JSContext* cx) override;
bool enqueuePromiseJob(JSContext* cx, JS::HandleObject promise,
JS::HandleObject job, JS::HandleObject allocationSite,
JS::HandleObject incumbentGlobal) override;
// MOZ_CAN_RUN_SCRIPT_BOUNDARY for now so we don't have to change SpiderMonkey
// headers. The caller presumably knows this can run script (like everything
// in SpiderMonkey!) and will deal.
void runJobs(JSContext* cx) override;
bool empty() const override;
class SavedMicroTaskQueue;
js::UniquePtr<SavedJobQueue> saveJobQueue(JSContext*) override;
CycleCollectedJSRuntime* mRuntime;
JSContext* mJSContext;
nsCOMPtr<dom::Exception> mPendingException;
nsThread* mOwningThread; // Manual refcounting to avoid include hell.
struct PendingIDBTransactionData {
nsCOMPtr<nsIRunnable> mTransaction;
uint32_t mRecursionDepth;
nsTArray<nsCOMPtr<nsIRunnable>> mStableStateEvents;
nsTArray<PendingIDBTransactionData> mPendingIDBTransactions;
uint32_t mBaseRecursionDepth;
bool mDoingStableStates;
// If set to none 0, microtasks will be processed only when recursion depth
// is the set value.
uint32_t mTargetedMicroTaskRecursionDepth;
uint32_t mMicroTaskLevel;
std::queue<RefPtr<MicroTaskRunnable>> mPendingMicroTaskRunnables;
std::queue<RefPtr<MicroTaskRunnable>> mDebuggerMicroTaskQueue;
// How many times the debugger has interrupted execution, possibly creating
// microtask checkpoints in places that they would not normally occur.
uint32_t mDebuggerRecursionDepth;
uint32_t mMicroTaskRecursionDepth;
// This implements about-to-be-notified rejected promises list in the spec.
typedef nsTArray<RefPtr<dom::Promise>> PromiseArray;
PromiseArray mAboutToBeNotifiedRejectedPromises;
// This is for the "outstanding rejected promises weak set" in the spec,
// We use different data structure and opposite logic here to achieve the same
// effect. Basically this is used for tracking the rejected promise that does
// NOT need firing a rejectionhandled event. We will check the table to see if
// firing rejectionhandled event is required when a rejected promise is being
// handled.
// The rejected promise will be stored in the table if
// - it is unhandled, and
// - The unhandledrejection is not yet fired.
// And be removed when
// - it is handled, or
// - A unhandledrejection is fired and it isn't being handled in event
// handler.
typedef nsRefPtrHashtable<nsUint64HashKey, dom::Promise> PromiseHashtable;
PromiseHashtable mPendingUnhandledRejections;
class NotifyUnhandledRejections final : public CancelableRunnable {
NotifyUnhandledRejections(CycleCollectedJSContext* aCx,
PromiseArray&& aPromises)
: CancelableRunnable("NotifyUnhandledRejections"),
mUnhandledRejections(std::move(aPromises)) {}
NS_IMETHOD Run() final;
nsresult Cancel() final;
CycleCollectedJSContext* mCx;
PromiseArray mUnhandledRejections;
FinalizationRegistryCleanup mFinalizationRegistryCleanup;
class MOZ_STACK_CLASS nsAutoMicroTask {
nsAutoMicroTask() {
CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
if (ccjs) {
MOZ_CAN_RUN_SCRIPT ~nsAutoMicroTask() {
CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
if (ccjs) {
} // namespace mozilla
#endif // mozilla_CycleCollectedJSContext_h