DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809
/* -*- 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 "nsThreadManager.h"
#include "nsThread.h"
#include "nsThreadPool.h"
#include "nsThreadUtils.h"
#include "nsIClassInfoImpl.h"
#include "nsTArray.h"
#include "nsXULAppAPI.h"
#include "MainThreadQueue.h"
#include "mozilla/AbstractThread.h"
#include "mozilla/ClearOnShutdown.h"
#include "mozilla/EventQueue.h"
#include "mozilla/Mutex.h"
#include "mozilla/Preferences.h"
#include "mozilla/SystemGroup.h"
#include "mozilla/StaticPtr.h"
#include "mozilla/TaskQueue.h"
#include "mozilla/ThreadEventQueue.h"
#include "mozilla/ThreadLocal.h"
#include "PrioritizedEventQueue.h"
#ifdef MOZ_CANARY
#  include <fcntl.h>
#  include <unistd.h>
#endif

#include "MainThreadIdlePeriod.h"
#include "InputEventStatistics.h"

using namespace mozilla;

static MOZ_THREAD_LOCAL(bool) sTLSIsMainThread;

bool NS_IsMainThreadTLSInitialized() { return sTLSIsMainThread.initialized(); }

class BackgroundEventTarget final : public nsIEventTarget {
 public:
  NS_DECL_THREADSAFE_ISUPPORTS
  NS_DECL_NSIEVENTTARGET_FULL

  BackgroundEventTarget();

  nsresult Init();

  already_AddRefed<nsISerialEventTarget> CreateBackgroundTaskQueue(
      const char* aName);

  void BeginShutdown(nsTArray<RefPtr<ShutdownPromise>>&);
  void FinishShutdown();

 private:
  ~BackgroundEventTarget() = default;

  nsCOMPtr<nsIThreadPool> mPool;
  nsCOMPtr<nsIThreadPool> mIOPool;

  Mutex mMutex;
  nsTArray<RefPtr<TaskQueue>> mTaskQueues;
};

NS_IMPL_ISUPPORTS(BackgroundEventTarget, nsIEventTarget)

BackgroundEventTarget::BackgroundEventTarget()
    : mMutex("BackgroundEventTarget::mMutex") {}

nsresult BackgroundEventTarget::Init() {
  nsCOMPtr<nsIThreadPool> pool(new nsThreadPool());
  NS_ENSURE_TRUE(pool, NS_ERROR_FAILURE);

  nsresult rv = pool->SetName(NS_LITERAL_CSTRING("BackgroundThreadPool"));
  NS_ENSURE_SUCCESS(rv, rv);

  // Use potentially more conservative stack size.
  rv = pool->SetThreadStackSize(nsIThreadManager::kThreadPoolStackSize);
  NS_ENSURE_SUCCESS(rv, rv);

  // For now just one thread. Can increase easily later if we want.
  rv = pool->SetThreadLimit(1);
  NS_ENSURE_SUCCESS(rv, rv);

  // Leave threads alive for up to 5 minutes
  rv = pool->SetIdleThreadTimeout(300000);
  NS_ENSURE_SUCCESS(rv, rv);

  // Initialize the background I/O event target.
  nsCOMPtr<nsIThreadPool> ioPool(new nsThreadPool());
  NS_ENSURE_TRUE(pool, NS_ERROR_FAILURE);

  rv = ioPool->SetName(NS_LITERAL_CSTRING("BgIOThreadPool"));
  NS_ENSURE_SUCCESS(rv, rv);

  // Use potentially more conservative stack size.
  rv = ioPool->SetThreadStackSize(nsIThreadManager::kThreadPoolStackSize);
  NS_ENSURE_SUCCESS(rv, rv);

  // For now just one thread. Can increase easily later if we want.
  rv = ioPool->SetThreadLimit(1);
  NS_ENSURE_SUCCESS(rv, rv);

  // Leave threads alive for up to 5 minutes
  rv = ioPool->SetIdleThreadTimeout(300000);
  NS_ENSURE_SUCCESS(rv, rv);

  pool.swap(mPool);
  ioPool.swap(mIOPool);

  return NS_OK;
}

NS_IMETHODIMP_(bool)
BackgroundEventTarget::IsOnCurrentThreadInfallible() {
  return mPool->IsOnCurrentThread() || mIOPool->IsOnCurrentThread();
}

NS_IMETHODIMP
BackgroundEventTarget::IsOnCurrentThread(bool* aValue) {
  bool value = false;
  if (NS_SUCCEEDED(mPool->IsOnCurrentThread(&value)) && value) {
    *aValue = value;
    return NS_OK;
  }
  return mIOPool->IsOnCurrentThread(aValue);
}

NS_IMETHODIMP
BackgroundEventTarget::Dispatch(already_AddRefed<nsIRunnable> aRunnable,
                                uint32_t aFlags) {
  // We need to be careful here, because if an event is getting dispatched here
  // from within TaskQueue::Runner::Run, it will be dispatched with
  // NS_DISPATCH_AT_END, but we might not be running the event on the same
  // pool, depending on which pool we were on and the dispatch flags.  If we
  // dispatch an event with NS_DISPATCH_AT_END to the wrong pool, the pool
  // may not process the event in a timely fashion, which can lead to deadlock.
  uint32_t flags = aFlags & ~NS_DISPATCH_EVENT_MAY_BLOCK;
  bool mayBlock = bool(aFlags & NS_DISPATCH_EVENT_MAY_BLOCK);
  nsCOMPtr<nsIThreadPool>& pool = mayBlock ? mIOPool : mPool;

  // If we're already running on the pool we want to dispatch to, we can
  // unconditionally add NS_DISPATCH_AT_END to indicate that we shouldn't spin
  // up a new thread.
  //
  // Otherwise, we should remove NS_DISPATCH_AT_END so we don't run into issues
  // like those in the above comment.
  if (pool->IsOnCurrentThread()) {
    flags |= NS_DISPATCH_AT_END;
  } else {
    flags &= ~NS_DISPATCH_AT_END;
  }

  return pool->Dispatch(std::move(aRunnable), flags);
}

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

NS_IMETHODIMP
BackgroundEventTarget::DelayedDispatch(already_AddRefed<nsIRunnable> aRunnable,
                                       uint32_t) {
  nsCOMPtr<nsIRunnable> dropRunnable(aRunnable);
  return NS_ERROR_NOT_IMPLEMENTED;
}

void BackgroundEventTarget::BeginShutdown(
    nsTArray<RefPtr<ShutdownPromise>>& promises) {
  for (auto& queue : mTaskQueues) {
    promises.AppendElement(queue->BeginShutdown());
  }
}

void BackgroundEventTarget::FinishShutdown() {
  mPool->Shutdown();
  mIOPool->Shutdown();
}

already_AddRefed<nsISerialEventTarget>
BackgroundEventTarget::CreateBackgroundTaskQueue(const char* aName) {
  MutexAutoLock lock(mMutex);

  RefPtr<TaskQueue> queue = new TaskQueue(do_AddRef(this), aName,
                                          /*aSupportsTailDispatch=*/false,
                                          /*aRetainFlags=*/true);
  nsCOMPtr<nsISerialEventTarget> target(queue->WrapAsEventTarget());

  mTaskQueues.AppendElement(queue.forget());

  return target.forget();
}

extern "C" {
// This uses the C language linkage because it's exposed to Rust
// via the xpcom/rust/moz_task crate.
bool NS_IsMainThread() { return sTLSIsMainThread.get(); }
}

void NS_SetMainThread() {
  if (!sTLSIsMainThread.init()) {
    MOZ_CRASH();
  }
  sTLSIsMainThread.set(true);
  MOZ_ASSERT(NS_IsMainThread());
}

#ifdef DEBUG

namespace mozilla {

void AssertIsOnMainThread() { MOZ_ASSERT(NS_IsMainThread(), "Wrong thread!"); }

}  // namespace mozilla

#endif

typedef nsTArray<NotNull<RefPtr<nsThread>>> nsThreadArray;

static bool sShutdownComplete;

//-----------------------------------------------------------------------------

/* static */
void nsThreadManager::ReleaseThread(void* aData) {
  if (sShutdownComplete) {
    // We've already completed shutdown and released the references to all or
    // our TLS wrappers. Don't try to release them again.
    return;
  }

  auto* thread = static_cast<nsThread*>(aData);

  if (thread->mHasTLSEntry) {
    thread->mHasTLSEntry = false;
    thread->Release();
  }
}

// statically allocated instance
NS_IMETHODIMP_(MozExternalRefCountType)
nsThreadManager::AddRef() { return 2; }
NS_IMETHODIMP_(MozExternalRefCountType)
nsThreadManager::Release() { return 1; }
NS_IMPL_CLASSINFO(nsThreadManager, nullptr,
                  nsIClassInfo::THREADSAFE | nsIClassInfo::SINGLETON,
                  NS_THREADMANAGER_CID)
NS_IMPL_QUERY_INTERFACE_CI(nsThreadManager, nsIThreadManager)
NS_IMPL_CI_INTERFACE_GETTER(nsThreadManager, nsIThreadManager)

namespace {

// Simple observer to monitor the beginning of the shutdown.
class ShutdownObserveHelper final : public nsIObserver,
                                    public nsSupportsWeakReference {
 public:
  NS_DECL_ISUPPORTS

  static nsresult Create(ShutdownObserveHelper** aObserver) {
    MOZ_ASSERT(aObserver);

    RefPtr<ShutdownObserveHelper> observer = new ShutdownObserveHelper();

    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
    if (NS_WARN_IF(!obs)) {
      return NS_ERROR_FAILURE;
    }

    nsresult rv =
        obs->AddObserver(observer, NS_XPCOM_SHUTDOWN_OBSERVER_ID, true);
    if (NS_WARN_IF(NS_FAILED(rv))) {
      return rv;
    }

    rv = obs->AddObserver(observer, "content-child-will-shutdown", true);
    if (NS_WARN_IF(NS_FAILED(rv))) {
      return rv;
    }

    observer.forget(aObserver);
    return NS_OK;
  }

  NS_IMETHOD
  Observe(nsISupports* aSubject, const char* aTopic,
          const char16_t* aData) override {
    if (!strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID) ||
        !strcmp(aTopic, "content-child-will-shutdown")) {
      mShuttingDown = true;
      return NS_OK;
    }

    return NS_OK;
  }

  bool ShuttingDown() const { return mShuttingDown; }

 private:
  explicit ShutdownObserveHelper() : mShuttingDown(false) {}

  ~ShutdownObserveHelper() = default;

  bool mShuttingDown;
};

NS_INTERFACE_MAP_BEGIN(ShutdownObserveHelper)
  NS_INTERFACE_MAP_ENTRY(nsIObserver)
  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIObserver)
NS_INTERFACE_MAP_END

NS_IMPL_ADDREF(ShutdownObserveHelper)
NS_IMPL_RELEASE(ShutdownObserveHelper)

StaticRefPtr<ShutdownObserveHelper> gShutdownObserveHelper;

}  // namespace

//-----------------------------------------------------------------------------

/*static*/ nsThreadManager& nsThreadManager::get() {
  static nsThreadManager sInstance;
  return sInstance;
}

/* static */
void nsThreadManager::InitializeShutdownObserver() {
  MOZ_ASSERT(!gShutdownObserveHelper);

  RefPtr<ShutdownObserveHelper> observer;
  nsresult rv = ShutdownObserveHelper::Create(getter_AddRefs(observer));
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return;
  }

  gShutdownObserveHelper = observer;
  ClearOnShutdown(&gShutdownObserveHelper);
}

nsThreadManager::nsThreadManager()
    : mCurThreadIndex(0), mMainPRThread(nullptr), mInitialized(false) {}

nsThreadManager::~nsThreadManager() = default;

nsresult nsThreadManager::Init() {
  // Child processes need to initialize the thread manager before they
  // initialize XPCOM in order to set up the crash reporter. This leads to
  // situations where we get initialized twice.
  if (mInitialized) {
    return NS_OK;
  }

  if (PR_NewThreadPrivateIndex(&mCurThreadIndex, ReleaseThread) == PR_FAILURE) {
    return NS_ERROR_FAILURE;
  }

#ifdef MOZ_CANARY
  const int flags = O_WRONLY | O_APPEND | O_CREAT | O_NONBLOCK;
  const mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
  char* env_var_flag = getenv("MOZ_KILL_CANARIES");
  sCanaryOutputFD =
      env_var_flag
          ? (env_var_flag[0] ? open(env_var_flag, flags, mode) : STDERR_FILENO)
          : 0;
#endif

  nsCOMPtr<nsIIdlePeriod> idlePeriod = new MainThreadIdlePeriod();

  mMainThread =
      CreateMainThread<ThreadEventQueue<PrioritizedEventQueue>>(idlePeriod);

  nsresult rv = mMainThread->InitCurrentThread();
  if (NS_FAILED(rv)) {
    mMainThread = nullptr;
    return rv;
  }

  // We need to keep a pointer to the current thread, so we can satisfy
  // GetIsMainThread calls that occur post-Shutdown.
  mMainThread->GetPRThread(&mMainPRThread);

  // Init AbstractThread.
  AbstractThread::InitTLS();
  AbstractThread::InitMainThread();

  // Initialize the background event target.
  RefPtr<BackgroundEventTarget> target(new BackgroundEventTarget());

  rv = target->Init();
  NS_ENSURE_SUCCESS(rv, rv);

  mBackgroundEventTarget = target.forget();

  mInitialized = true;

  return NS_OK;
}

void nsThreadManager::Shutdown() {
  MOZ_ASSERT(NS_IsMainThread(), "shutdown not called from main thread");

  // Prevent further access to the thread manager (no more new threads!)
  //
  // What happens if shutdown happens before NewThread completes?
  // We Shutdown() the new thread, and return error if we've started Shutdown
  // between when NewThread started, and when the thread finished initializing
  // and registering with ThreadManager.
  //
  mInitialized = false;

  // Empty the main thread event queue before we begin shutting down threads.
  NS_ProcessPendingEvents(mMainThread);

  typedef typename ShutdownPromise::AllPromiseType AllPromise;
  typename AllPromise::ResolveOrRejectValue val;
  using ResolveValueT = typename AllPromise::ResolveValueType;
  using RejectValueT = typename AllPromise::RejectValueType;

  nsTArray<RefPtr<ShutdownPromise>> promises;
  mBackgroundEventTarget->BeginShutdown(promises);

  RefPtr<AllPromise> complete = ShutdownPromise::All(mMainThread, promises);

  bool taskQueuesShutdown = false;

  complete->Then(
      mMainThread, __func__,
      [&](const ResolveValueT& aResolveValue) {
        mBackgroundEventTarget->FinishShutdown();
        taskQueuesShutdown = true;
      },
      [&](RejectValueT aRejectValue) {
        mBackgroundEventTarget->FinishShutdown();
        taskQueuesShutdown = true;
      });

  // Wait for task queues to shutdown, so we don't shut down the underlying
  // threads of the background event target in the block below, thereby
  // preventing the task queues from emptying, preventing the shutdown promises
  // from resolving, and prevent anything checking `taskQueuesShutdown` from
  // working.
  ::SpinEventLoopUntil([&]() { return taskQueuesShutdown; }, mMainThread);

  {
    // We gather the threads from the hashtable into a list, so that we avoid
    // holding the enumerator lock while calling nsIThread::Shutdown.
    nsTArray<RefPtr<nsThread>> threadsToShutdown;
    for (auto* thread : nsThread::Enumerate()) {
      if (thread->ShutdownRequired()) {
        threadsToShutdown.AppendElement(thread);
      }
    }

    // It's tempting to walk the list of threads here and tell them each to stop
    // accepting new events, but that could lead to badness if one of those
    // threads is stuck waiting for a response from another thread.  To do it
    // right, we'd need some way to interrupt the threads.
    //
    // Instead, we process events on the current thread while waiting for
    // threads to shutdown.  This means that we have to preserve a mostly
    // functioning world until such time as the threads exit.

    // Shutdown all threads that require it (join with threads that we created).
    for (auto& thread : threadsToShutdown) {
      thread->Shutdown();
    }
  }

  // NB: It's possible that there are events in the queue that want to *start*
  // an asynchronous shutdown. But we have already shutdown the threads above,
  // so there's no need to worry about them. We only have to wait for all
  // in-flight asynchronous thread shutdowns to complete.
  mMainThread->WaitForAllAsynchronousShutdowns();

  // In case there are any more events somehow...
  NS_ProcessPendingEvents(mMainThread);

  // There are no more background threads at this point.

  // Normally thread shutdown clears the observer for the thread, but since the
  // main thread is special we do it manually here after we're sure all events
  // have been processed.
  mMainThread->SetObserver(nullptr);

  mBackgroundEventTarget = nullptr;

  // Release main thread object.
  mMainThread = nullptr;

  // Remove the TLS entry for the main thread.
  PR_SetThreadPrivate(mCurThreadIndex, nullptr);

  {
    // Cleanup the last references to any threads which haven't shut down yet.
    nsTArray<RefPtr<nsThread>> threads;
    for (auto* thread : nsThread::Enumerate()) {
      if (thread->mHasTLSEntry) {
        threads.AppendElement(dont_AddRef(thread));
        thread->mHasTLSEntry = false;
      }
    }
  }

  // xpcshell tests sometimes leak the main thread. They don't enable leak
  // checking, so that doesn't cause the test to fail, but leaving the entry in
  // the thread list triggers an assertion, which does.
  nsThread::ClearThreadList();

  sShutdownComplete = true;
}

void nsThreadManager::RegisterCurrentThread(nsThread& aThread) {
  MOZ_ASSERT(aThread.GetPRThread() == PR_GetCurrentThread(), "bad aThread");

  aThread.AddRef();  // for TLS entry
  aThread.mHasTLSEntry = true;
  PR_SetThreadPrivate(mCurThreadIndex, &aThread);
}

void nsThreadManager::UnregisterCurrentThread(nsThread& aThread) {
  MOZ_ASSERT(aThread.GetPRThread() == PR_GetCurrentThread(), "bad aThread");

  PR_SetThreadPrivate(mCurThreadIndex, nullptr);
  // Ref-count balanced via ReleaseThread
}

nsThread* nsThreadManager::CreateCurrentThread(
    SynchronizedEventQueue* aQueue, nsThread::MainThreadFlag aMainThread) {
  // Make sure we don't have an nsThread yet.
  MOZ_ASSERT(!PR_GetThreadPrivate(mCurThreadIndex));

  if (!mInitialized) {
    return nullptr;
  }

  RefPtr<nsThread> thread = new nsThread(WrapNotNull(aQueue), aMainThread, 0);
  if (!thread || NS_FAILED(thread->InitCurrentThread())) {
    return nullptr;
  }

  return thread.get();  // reference held in TLS
}

nsresult nsThreadManager::DispatchToBackgroundThread(nsIRunnable* aEvent,
                                                     uint32_t aDispatchFlags) {
  if (!mInitialized) {
    return NS_ERROR_FAILURE;
  }

  nsCOMPtr<nsIEventTarget> backgroundTarget(mBackgroundEventTarget);
  return backgroundTarget->Dispatch(aEvent, aDispatchFlags);
}

already_AddRefed<nsISerialEventTarget>
nsThreadManager::CreateBackgroundTaskQueue(const char* aName) {
  if (!mInitialized) {
    return nullptr;
  }

  return mBackgroundEventTarget->CreateBackgroundTaskQueue(aName);
}

nsThread* nsThreadManager::GetCurrentThread() {
  // read thread local storage
  void* data = PR_GetThreadPrivate(mCurThreadIndex);
  if (data) {
    return static_cast<nsThread*>(data);
  }

  if (!mInitialized) {
    return nullptr;
  }

  // OK, that's fine.  We'll dynamically create one :-)
  //
  // We assume that if we're implicitly creating a thread here that it doesn't
  // want an event queue. Any thread which wants an event queue should
  // explicitly create its nsThread wrapper.
  RefPtr<nsThread> thread = new nsThread();
  if (!thread || NS_FAILED(thread->InitCurrentThread())) {
    return nullptr;
  }

  return thread.get();  // reference held in TLS
}

bool nsThreadManager::IsNSThread() const {
  if (!mInitialized) {
    return false;
  }
  if (auto* thread = (nsThread*)PR_GetThreadPrivate(mCurThreadIndex)) {
    return thread->EventQueue();
  }
  return false;
}

NS_IMETHODIMP
nsThreadManager::NewThread(uint32_t aCreationFlags, uint32_t aStackSize,
                           nsIThread** aResult) {
  return NewNamedThread(NS_LITERAL_CSTRING(""), aStackSize, aResult);
}

NS_IMETHODIMP
nsThreadManager::NewNamedThread(const nsACString& aName, uint32_t aStackSize,
                                nsIThread** aResult) {
  // Note: can be called from arbitrary threads

  // No new threads during Shutdown
  if (NS_WARN_IF(!mInitialized)) {
    return NS_ERROR_NOT_INITIALIZED;
  }

  RefPtr<ThreadEventQueue<EventQueue>> queue =
      new ThreadEventQueue<EventQueue>(MakeUnique<EventQueue>());
  RefPtr<nsThread> thr =
      new nsThread(WrapNotNull(queue), nsThread::NOT_MAIN_THREAD, aStackSize);
  nsresult rv =
      thr->Init(aName);  // Note: blocks until the new thread has been set up
  if (NS_FAILED(rv)) {
    return rv;
  }

  // At this point, we expect that the thread has been registered in
  // mThreadByPRThread; however, it is possible that it could have also been
  // replaced by now, so we cannot really assert that it was added.  Instead,
  // kill it if we entered Shutdown() during/before Init()

  if (NS_WARN_IF(!mInitialized)) {
    if (thr->ShutdownRequired()) {
      thr->Shutdown();  // ok if it happens multiple times
    }
    return NS_ERROR_NOT_INITIALIZED;
  }

  thr.forget(aResult);
  return NS_OK;
}

NS_IMETHODIMP
nsThreadManager::GetMainThread(nsIThread** aResult) {
  // Keep this functioning during Shutdown
  if (!mMainThread) {
    if (!NS_IsMainThread()) {
      NS_WARNING(
          "Called GetMainThread but there isn't a main thread and "
          "we're not the main thread.");
    }
    return NS_ERROR_NOT_INITIALIZED;
  }
  NS_ADDREF(*aResult = mMainThread);
  return NS_OK;
}

NS_IMETHODIMP
nsThreadManager::GetCurrentThread(nsIThread** aResult) {
  // Keep this functioning during Shutdown
  if (!mMainThread) {
    return NS_ERROR_NOT_INITIALIZED;
  }
  *aResult = GetCurrentThread();
  if (!*aResult) {
    return NS_ERROR_OUT_OF_MEMORY;
  }
  NS_ADDREF(*aResult);
  return NS_OK;
}

NS_IMETHODIMP
nsThreadManager::SpinEventLoopUntil(nsINestedEventLoopCondition* aCondition) {
  return SpinEventLoopUntilInternal(aCondition, false);
}

NS_IMETHODIMP
nsThreadManager::SpinEventLoopUntilOrShutdown(
    nsINestedEventLoopCondition* aCondition) {
  return SpinEventLoopUntilInternal(aCondition, true);
}

nsresult nsThreadManager::SpinEventLoopUntilInternal(
    nsINestedEventLoopCondition* aCondition, bool aCheckingShutdown) {
  nsCOMPtr<nsINestedEventLoopCondition> condition(aCondition);
  nsresult rv = NS_OK;

  // Nothing to do if already shutting down. Note that gShutdownObserveHelper is
  // nullified on shutdown.
  if (aCheckingShutdown &&
      (!gShutdownObserveHelper || gShutdownObserveHelper->ShuttingDown())) {
    return NS_OK;
  }

  if (!mozilla::SpinEventLoopUntil([&]() -> bool {
        // Shutting down is started.
        if (aCheckingShutdown && (!gShutdownObserveHelper ||
                                  gShutdownObserveHelper->ShuttingDown())) {
          return true;
        }

        bool isDone = false;
        rv = condition->IsDone(&isDone);
        // JS failure should be unusual, but we need to stop and propagate
        // the error back to the caller.
        if (NS_FAILED(rv)) {
          return true;
        }

        return isDone;
      })) {
    // We stopped early for some reason, which is unexpected.
    return NS_ERROR_UNEXPECTED;
  }

  // If we exited when the condition told us to, we need to return whether
  // the condition encountered failure when executing.
  return rv;
}

NS_IMETHODIMP
nsThreadManager::SpinEventLoopUntilEmpty() {
  nsIThread* thread = NS_GetCurrentThread();

  while (NS_HasPendingEvents(thread)) {
    (void)NS_ProcessNextEvent(thread, false);
  }

  return NS_OK;
}

NS_IMETHODIMP
nsThreadManager::GetSystemGroupEventTarget(nsIEventTarget** aTarget) {
  nsCOMPtr<nsIEventTarget> target =
      SystemGroup::EventTargetFor(TaskCategory::Other);
  target.forget(aTarget);
  return NS_OK;
}

uint32_t nsThreadManager::GetHighestNumberOfThreads() {
  return nsThread::MaxActiveThreads();
}

NS_IMETHODIMP
nsThreadManager::DispatchToMainThread(nsIRunnable* aEvent, uint32_t aPriority,
                                      uint8_t aArgc) {
  // Note: C++ callers should instead use NS_DispatchToMainThread.
  MOZ_ASSERT(NS_IsMainThread());

  // Keep this functioning during Shutdown
  if (NS_WARN_IF(!mMainThread)) {
    return NS_ERROR_NOT_INITIALIZED;
  }
  // If aPriority wasn't explicitly passed, that means it should be treated as
  // PRIORITY_NORMAL.
  if (aArgc > 0 && aPriority != nsIRunnablePriority::PRIORITY_NORMAL) {
    nsCOMPtr<nsIRunnable> event(aEvent);
    return mMainThread->DispatchFromScript(
        new PrioritizableRunnable(event.forget(), aPriority), 0);
  }
  return mMainThread->DispatchFromScript(aEvent, 0);
}

void nsThreadManager::EnableMainThreadEventPrioritization() {
  MOZ_ASSERT(NS_IsMainThread());
  InputEventStatistics::Get().SetEnable(true);
  mMainThread->EnableInputEventPrioritization();
}

void nsThreadManager::FlushInputEventPrioritization() {
  MOZ_ASSERT(NS_IsMainThread());
  mMainThread->FlushInputEventPrioritization();
}

void nsThreadManager::SuspendInputEventPrioritization() {
  MOZ_ASSERT(NS_IsMainThread());
  mMainThread->SuspendInputEventPrioritization();
}

void nsThreadManager::ResumeInputEventPrioritization() {
  MOZ_ASSERT(NS_IsMainThread());
  mMainThread->ResumeInputEventPrioritization();
}

// static
bool nsThreadManager::MainThreadHasPendingHighPriorityEvents() {
  MOZ_ASSERT(NS_IsMainThread());
  bool retVal = false;
  if (get().mMainThread) {
    get().mMainThread->HasPendingHighPriorityEvents(&retVal);
  }
  return retVal;
}

NS_IMETHODIMP
nsThreadManager::IdleDispatchToMainThread(nsIRunnable* aEvent,
                                          uint32_t aTimeout) {
  // Note: C++ callers should instead use NS_DispatchToThreadQueue or
  // NS_DispatchToCurrentThreadQueue.
  MOZ_ASSERT(NS_IsMainThread());

  nsCOMPtr<nsIRunnable> event(aEvent);
  if (aTimeout) {
    return NS_DispatchToThreadQueue(event.forget(), aTimeout, mMainThread,
                                    EventQueuePriority::Idle);
  }

  return NS_DispatchToThreadQueue(event.forget(), mMainThread,
                                  EventQueuePriority::Idle);
}