gecko-dev/dom/worklet/WorkletThread.cpp

/* -*- 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 http://mozilla.org/MPL/2.0/. */

#include "WorkletThread.h"
#include "prthread.h"
#include "nsContentUtils.h"
#include "nsCycleCollector.h"
#include "mozilla/dom/AtomList.h"
#include "mozilla/EventQueue.h"
#include "mozilla/ThreadEventQueue.h"

namespace mozilla {
namespace dom {

namespace {

// The size of the worklet runtime heaps in bytes.
#define WORKLET_DEFAULT_RUNTIME_HEAPSIZE 32 * 1024 * 1024

// The size of the generational GC nursery for worklet, in bytes.
#define WORKLET_DEFAULT_NURSERY_SIZE 1 * 1024 * 1024

// The C stack size. We use the same stack size on all platforms for
// consistency.
const uint32_t kWorkletStackSize = 256 * sizeof(size_t) * 1024;

// Helper functions

bool PreserveWrapper(JSContext* aCx, JS::HandleObject aObj) {
  MOZ_ASSERT(aCx);
  MOZ_ASSERT(aObj);
  MOZ_ASSERT(mozilla::dom::IsDOMObject(aObj));
  return mozilla::dom::TryPreserveWrapper(aObj);
}

void DestroyWorkletPrincipals(JSPrincipals* aPrincipals) {
  MOZ_ASSERT_UNREACHABLE(
      "Worklet principals refcount should never fall below one");
}

JSObject* Wrap(JSContext* aCx, JS::HandleObject aExisting,
               JS::HandleObject aObj) {
  if (aExisting) {
    js::Wrapper::Renew(aExisting, aObj,
                       &js::OpaqueCrossCompartmentWrapper::singleton);
  }

  return js::Wrapper::New(aCx, aObj,
                          &js::OpaqueCrossCompartmentWrapper::singleton);
}

const JSWrapObjectCallbacks WrapObjectCallbacks = {
    Wrap,
    nullptr,
};

}  // namespace

// This classes control CC in the worklet thread.

class WorkletJSRuntime final : public mozilla::CycleCollectedJSRuntime {
 public:
  explicit WorkletJSRuntime(JSContext* aCx) : CycleCollectedJSRuntime(aCx) {}

  ~WorkletJSRuntime() override = default;

  virtual void PrepareForForgetSkippable() override {}

  virtual void BeginCycleCollectionCallback() override {}

  virtual void EndCycleCollectionCallback(
      CycleCollectorResults& aResults) override {}

  virtual void DispatchDeferredDeletion(bool aContinuation,
                                        bool aPurge) override {
    MOZ_ASSERT(!aContinuation);
    nsCycleCollector_doDeferredDeletion();
  }

  virtual void CustomGCCallback(JSGCStatus aStatus) override {
    // nsCycleCollector_collect() requires a cycle collector but
    // ~WorkletJSContext calls nsCycleCollector_shutdown() and the base class
    // destructor will trigger a final GC.  The nsCycleCollector_collect()
    // call can be skipped in this GC as ~CycleCollectedJSContext removes the
    // context from |this|.
    if (aStatus == JSGC_END && !Contexts().isEmpty()) {
      nsCycleCollector_collect(nullptr);
    }
  }
};

class WorkletJSContext final : public CycleCollectedJSContext {
 public:
  WorkletJSContext() {
    MOZ_ASSERT(!NS_IsMainThread());

    nsCycleCollector_startup();
  }

  ~WorkletJSContext() override {
    MOZ_ASSERT(!NS_IsMainThread());

    JSContext* cx = MaybeContext();
    if (!cx) {
      return;  // Initialize() must have failed
    }

    nsCycleCollector_shutdown();
  }

  WorkletJSContext* GetAsWorkletJSContext() override { return this; }

  CycleCollectedJSRuntime* CreateRuntime(JSContext* aCx) override {
    return new WorkletJSRuntime(aCx);
  }

  nsresult Initialize(JSRuntime* aParentRuntime) {
    MOZ_ASSERT(!NS_IsMainThread());

    nsresult rv = CycleCollectedJSContext::Initialize(
        aParentRuntime, WORKLET_DEFAULT_RUNTIME_HEAPSIZE,
        WORKLET_DEFAULT_NURSERY_SIZE);
    if (NS_WARN_IF(NS_FAILED(rv))) {
      return rv;
    }

    JSContext* cx = Context();

    js::SetPreserveWrapperCallback(cx, PreserveWrapper);
    JS_InitDestroyPrincipalsCallback(cx, DestroyWorkletPrincipals);
    JS_SetWrapObjectCallbacks(cx, &WrapObjectCallbacks);
    JS_SetFutexCanWait(cx);

    return NS_OK;
  }

  void DispatchToMicroTask(
      already_AddRefed<MicroTaskRunnable> aRunnable) override {
    RefPtr<MicroTaskRunnable> runnable(aRunnable);

    MOZ_ASSERT(!NS_IsMainThread());
    MOZ_ASSERT(runnable);

    JSContext* cx = Context();
    MOZ_ASSERT(cx);

#ifdef DEBUG
    JS::Rooted<JSObject*> global(cx, JS::CurrentGlobalOrNull(cx));
    MOZ_ASSERT(global);
#endif

    JS::JobQueueMayNotBeEmpty(cx);
    GetMicroTaskQueue().push(runnable.forget());
  }

  bool IsSystemCaller() const override {
    // Currently no support for special system worklet privileges.
    return false;
  }
};

// This is the first runnable to be dispatched. It calls the RunEventLoop() so
// basically everything happens into this runnable. The reason behind this
// approach is that, when the Worklet is terminated, it must not have any JS in
// stack, but, because we have CC, nsIThread creates an AutoNoJSAPI object by
// default. Using this runnable, CC exists only into it.
class WorkletThread::PrimaryRunnable final : public Runnable {
 public:
  explicit PrimaryRunnable(WorkletThread* aWorkletThread)
      : Runnable("WorkletThread::PrimaryRunnable"),
        mWorkletThread(aWorkletThread) {
    MOZ_ASSERT(aWorkletThread);
    MOZ_ASSERT(NS_IsMainThread());
  }

  NS_IMETHOD
  Run() override {
    mWorkletThread->RunEventLoop();
    return NS_OK;
  }

 private:
  RefPtr<WorkletThread> mWorkletThread;
};

// This is the last runnable to be dispatched. It calls the TerminateInternal()
class WorkletThread::TerminateRunnable final : public Runnable {
 public:
  explicit TerminateRunnable(WorkletThread* aWorkletThread)
      : Runnable("WorkletThread::TerminateRunnable"),
        mWorkletThread(aWorkletThread) {
    MOZ_ASSERT(aWorkletThread);
    MOZ_ASSERT(NS_IsMainThread());
  }

  NS_IMETHOD
  Run() override {
    mWorkletThread->TerminateInternal();
    return NS_OK;
  }

 private:
  RefPtr<WorkletThread> mWorkletThread;
};

WorkletThread::WorkletThread()
    : nsThread(MakeNotNull<ThreadEventQueue<mozilla::EventQueue>*>(
                   MakeUnique<mozilla::EventQueue>()),
               nsThread::NOT_MAIN_THREAD, kWorkletStackSize),
      mExitLoop(false),
      mIsTerminating(false) {
  MOZ_ASSERT(NS_IsMainThread());
  nsContentUtils::RegisterShutdownObserver(this);
}

WorkletThread::~WorkletThread() {
  // This should be set during the termination step.
  MOZ_ASSERT(mExitLoop);
}

// static
already_AddRefed<WorkletThread> WorkletThread::Create() {
  RefPtr<WorkletThread> thread = new WorkletThread();
  if (NS_WARN_IF(NS_FAILED(thread->Init()))) {
    return nullptr;
  }

  RefPtr<PrimaryRunnable> runnable = new PrimaryRunnable(thread);
  if (NS_WARN_IF(NS_FAILED(thread->DispatchRunnable(runnable.forget())))) {
    return nullptr;
  }

  return thread.forget();
}

nsresult WorkletThread::DispatchRunnable(
    already_AddRefed<nsIRunnable> aRunnable) {
  nsCOMPtr<nsIRunnable> runnable(aRunnable);
  return nsThread::Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
}

NS_IMETHODIMP
WorkletThread::DispatchFromScript(nsIRunnable* aRunnable, uint32_t aFlags) {
  nsCOMPtr<nsIRunnable> runnable(aRunnable);
  return Dispatch(runnable.forget(), aFlags);
}

NS_IMETHODIMP
WorkletThread::Dispatch(already_AddRefed<nsIRunnable> aRunnable,
                        uint32_t aFlags) {
  nsCOMPtr<nsIRunnable> runnable(aRunnable);

  // Worklet only supports asynchronous dispatch.
  if (NS_WARN_IF(aFlags != NS_DISPATCH_NORMAL)) {
    return NS_ERROR_UNEXPECTED;
  }

  return nsThread::Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
}

NS_IMETHODIMP
WorkletThread::DelayedDispatch(already_AddRefed<nsIRunnable>, uint32_t aFlags) {
  return NS_ERROR_NOT_IMPLEMENTED;
}

/* static */
void WorkletThread::EnsureCycleCollectedJSContext(JSRuntime* aParentRuntime) {
  CycleCollectedJSContext* ccjscx = CycleCollectedJSContext::Get();
  if (ccjscx) {
    MOZ_ASSERT(ccjscx->GetAsWorkletJSContext());
    return;
  }

  WorkletJSContext* context = new WorkletJSContext();
  nsresult rv = context->Initialize(aParentRuntime);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    // TODO: error propagation
    return;
  }

  // FIXME: JS_SetDefaultLocale
  // FIXME: JSSettings
  // FIXME: JS_SetNativeStackQuota
  // FIXME: JS_SetSecurityCallbacks
  // FIXME: JS::SetAsyncTaskCallbacks
  // FIXME: JS_AddInterruptCallback
  // FIXME: JS::SetCTypesActivityCallback
  // FIXME: JS_SetGCZeal

  if (!JS::InitSelfHostedCode(context->Context())) {
    // TODO: error propagation
    return;
  }
}

void WorkletThread::RunEventLoop() {
  MOZ_ASSERT(!NS_IsMainThread());

  PR_SetCurrentThreadName("worklet");

  while (!mExitLoop) {
    MOZ_ALWAYS_TRUE(NS_ProcessNextEvent(this, /* wait: */ true));
  }

  DeleteCycleCollectedJSContext();
}

void WorkletThread::Terminate() {
  MOZ_ASSERT(NS_IsMainThread());

  if (mIsTerminating) {
    // nsThread::Dispatch() would leak the runnable if the event queue is no
    // longer accepting runnables.
    return;
  }

  mIsTerminating = true;

  nsContentUtils::UnregisterShutdownObserver(this);

  RefPtr<TerminateRunnable> runnable = new TerminateRunnable(this);
  DispatchRunnable(runnable.forget());
}

void WorkletThread::TerminateInternal() {
  AssertIsOnWorkletThread();

  mExitLoop = true;

  nsCOMPtr<nsIRunnable> runnable = NewRunnableMethod(
      "WorkletThread::Shutdown", this, &WorkletThread::Shutdown);
  NS_DispatchToMainThread(runnable);
}

/* static */
void WorkletThread::DeleteCycleCollectedJSContext() {
  CycleCollectedJSContext* ccjscx = CycleCollectedJSContext::Get();
  if (!ccjscx) {
    return;
  }

  WorkletJSContext* workletjscx = ccjscx->GetAsWorkletJSContext();
  MOZ_ASSERT(workletjscx);
  delete workletjscx;
}

/* static */
bool WorkletThread::IsOnWorkletThread() {
  CycleCollectedJSContext* ccjscx = CycleCollectedJSContext::Get();
  return ccjscx && ccjscx->GetAsWorkletJSContext();
}

/* static */
void WorkletThread::AssertIsOnWorkletThread() {
  MOZ_ASSERT(IsOnWorkletThread());
}

// nsIObserver
NS_IMETHODIMP
WorkletThread::Observe(nsISupports* aSubject, const char* aTopic,
                       const char16_t*) {
  MOZ_ASSERT(strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID) == 0);

  Terminate();
  return NS_OK;
}

NS_IMPL_ISUPPORTS_INHERITED(WorkletThread, nsThread, nsIObserver)

}  // namespace dom
}  // namespace mozilla