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.

Header

Mercurial (1047d440caa5)

VCS Links

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
/* -*- 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 "mozilla/mscom/MainThreadHandoff.h"

#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/Move.h"
#include "mozilla/mscom/AgileReference.h"
#include "mozilla/mscom/InterceptorLog.h"
#include "mozilla/mscom/Registration.h"
#include "mozilla/mscom/Utils.h"
#include "mozilla/TimeStamp.h"
#include "mozilla/ThreadLocal.h"
#include "mozilla/Unused.h"
#include "nsThreadUtils.h"
#include "nsProxyRelease.h"

using mozilla::DebugOnly;
using mozilla::mscom::AgileReference;

namespace {

class MOZ_NON_TEMPORARY_CLASS InParamWalker : private ICallFrameWalker {
 public:
  InParamWalker() : mPreHandoff(true) {}

  void SetHandoffDone() {
    mPreHandoff = false;
    mAgileRefsItr = mAgileRefs.begin();
  }

  HRESULT Walk(ICallFrame* aFrame) {
    MOZ_ASSERT(aFrame);
    if (!aFrame) {
      return E_INVALIDARG;
    }

    return aFrame->WalkFrame(CALLFRAME_WALK_IN, this);
  }

 private:
  // IUnknown
  STDMETHODIMP QueryInterface(REFIID aIid, void** aOutInterface) override {
    if (!aOutInterface) {
      return E_INVALIDARG;
    }
    *aOutInterface = nullptr;

    if (aIid == IID_IUnknown || aIid == IID_ICallFrameWalker) {
      *aOutInterface = static_cast<ICallFrameWalker*>(this);
      return S_OK;
    }

    return E_NOINTERFACE;
  }

  STDMETHODIMP_(ULONG) AddRef() override { return 2; }

  STDMETHODIMP_(ULONG) Release() override { return 1; }

  // ICallFrameWalker
  STDMETHODIMP OnWalkInterface(REFIID aIid, PVOID* aInterface, BOOL aIn,
                               BOOL aOut) override {
    MOZ_ASSERT(aIn);
    if (!aIn) {
      return E_UNEXPECTED;
    }

    IUnknown* origInterface = static_cast<IUnknown*>(*aInterface);
    if (!origInterface) {
      // Nothing to do
      return S_OK;
    }

    if (mPreHandoff) {
      mAgileRefs.AppendElement(AgileReference(aIid, origInterface));
      return S_OK;
    }

    MOZ_ASSERT(mAgileRefsItr != mAgileRefs.end());
    if (mAgileRefsItr == mAgileRefs.end()) {
      return E_UNEXPECTED;
    }

    HRESULT hr = mAgileRefsItr->Resolve(aIid, aInterface);
    MOZ_ASSERT(SUCCEEDED(hr));
    if (SUCCEEDED(hr)) {
      ++mAgileRefsItr;
    }

    return hr;
  }

  InParamWalker(const InParamWalker&) = delete;
  InParamWalker(InParamWalker&&) = delete;
  InParamWalker& operator=(const InParamWalker&) = delete;
  InParamWalker& operator=(InParamWalker&&) = delete;

 private:
  bool mPreHandoff;
  AutoTArray<AgileReference, 1> mAgileRefs;
  nsTArray<AgileReference>::iterator mAgileRefsItr;
};

class HandoffRunnable : public mozilla::Runnable {
 public:
  explicit HandoffRunnable(ICallFrame* aCallFrame, IUnknown* aTargetInterface)
      : Runnable("HandoffRunnable"),
        mCallFrame(aCallFrame),
        mTargetInterface(aTargetInterface),
        mResult(E_UNEXPECTED) {
    DebugOnly<HRESULT> hr = mInParamWalker.Walk(aCallFrame);
    MOZ_ASSERT(SUCCEEDED(hr));
  }

  NS_IMETHOD Run() override {
    mInParamWalker.SetHandoffDone();
    // We declare hr a DebugOnly because if mInParamWalker.Walk() fails, then
    // mCallFrame->Invoke will fail anyway.
    DebugOnly<HRESULT> hr = mInParamWalker.Walk(mCallFrame);
    MOZ_ASSERT(SUCCEEDED(hr));
    mResult = mCallFrame->Invoke(mTargetInterface);
    return NS_OK;
  }

  HRESULT GetResult() const { return mResult; }

 private:
  ICallFrame* mCallFrame;
  InParamWalker mInParamWalker;
  IUnknown* mTargetInterface;
  HRESULT mResult;
};

class MOZ_RAII SavedCallFrame final {
 public:
  explicit SavedCallFrame(mozilla::NotNull<ICallFrame*> aFrame)
      : mCallFrame(aFrame) {
    static const bool sIsInit = tlsFrame.init();
    MOZ_ASSERT(sIsInit);
    MOZ_ASSERT(!tlsFrame.get());
    tlsFrame.set(this);
    Unused << sIsInit;
  }

  ~SavedCallFrame() {
    MOZ_ASSERT(tlsFrame.get());
    tlsFrame.set(nullptr);
  }

  HRESULT GetIidAndMethod(mozilla::NotNull<IID*> aIid,
                          mozilla::NotNull<ULONG*> aMethod) const {
    return mCallFrame->GetIIDAndMethod(aIid, aMethod);
  }

  static const SavedCallFrame& Get() {
    SavedCallFrame* saved = tlsFrame.get();
    MOZ_ASSERT(saved);

    return *saved;
  }

  SavedCallFrame(const SavedCallFrame&) = delete;
  SavedCallFrame(SavedCallFrame&&) = delete;
  SavedCallFrame& operator=(const SavedCallFrame&) = delete;
  SavedCallFrame& operator=(SavedCallFrame&&) = delete;

 private:
  ICallFrame* mCallFrame;

 private:
  static MOZ_THREAD_LOCAL(SavedCallFrame*) tlsFrame;
};

MOZ_THREAD_LOCAL(SavedCallFrame*) SavedCallFrame::tlsFrame;

class MOZ_RAII LogEvent final {
 public:
  LogEvent() : mCallStart(mozilla::TimeStamp::Now()) {}

  ~LogEvent() {
    if (mCapturedFrame.IsEmpty()) {
      return;
    }

    mozilla::TimeStamp callEnd(TimeStamp::Now());
    mozilla::TimeDuration totalTime(callEnd - mCallStart);
    mozilla::TimeDuration overhead(totalTime - mGeckoDuration -
                                   mCaptureDuration);

    mozilla::mscom::InterceptorLog::Event(mCapturedFrame, overhead,
                                          mGeckoDuration);
  }

  void CaptureFrame(ICallFrame* aFrame, IUnknown* aTarget,
                    const mozilla::TimeDuration& aGeckoDuration) {
    mozilla::TimeStamp captureStart(TimeStamp::Now());

    mozilla::mscom::InterceptorLog::CaptureFrame(aFrame, aTarget,
                                                 mCapturedFrame);
    mGeckoDuration = aGeckoDuration;

    mozilla::TimeStamp captureEnd(TimeStamp::Now());

    // Make sure that the time we spent in CaptureFrame isn't charged against
    // overall overhead
    mCaptureDuration = captureEnd - captureStart;
  }

  LogEvent(const LogEvent&) = delete;
  LogEvent(LogEvent&&) = delete;
  LogEvent& operator=(const LogEvent&) = delete;
  LogEvent& operator=(LogEvent&&) = delete;

 private:
  mozilla::TimeStamp mCallStart;
  mozilla::TimeDuration mGeckoDuration;
  mozilla::TimeDuration mCaptureDuration;
  nsAutoCString mCapturedFrame;
};

}  // anonymous namespace

namespace mozilla {
namespace mscom {

/* static */
HRESULT MainThreadHandoff::Create(IHandlerProvider* aHandlerProvider,
                                  IInterceptorSink** aOutput) {
  RefPtr<MainThreadHandoff> handoff(new MainThreadHandoff(aHandlerProvider));
  return handoff->QueryInterface(IID_IInterceptorSink, (void**)aOutput);
}

MainThreadHandoff::MainThreadHandoff(IHandlerProvider* aHandlerProvider)
    : mRefCnt(0), mHandlerProvider(aHandlerProvider) {}

MainThreadHandoff::~MainThreadHandoff() { MOZ_ASSERT(NS_IsMainThread()); }

HRESULT
MainThreadHandoff::QueryInterface(REFIID riid, void** ppv) {
  IUnknown* punk = nullptr;
  if (!ppv) {
    return E_INVALIDARG;
  }

  if (riid == IID_IUnknown || riid == IID_ICallFrameEvents ||
      riid == IID_IInterceptorSink) {
    punk = static_cast<IInterceptorSink*>(this);
  } else if (riid == IID_ICallFrameWalker) {
    punk = static_cast<ICallFrameWalker*>(this);
  }

  *ppv = punk;
  if (!punk) {
    return E_NOINTERFACE;
  }

  punk->AddRef();
  return S_OK;
}

ULONG
MainThreadHandoff::AddRef() {
  return (ULONG)InterlockedIncrement((LONG*)&mRefCnt);
}

ULONG
MainThreadHandoff::Release() {
  ULONG newRefCnt = (ULONG)InterlockedDecrement((LONG*)&mRefCnt);
  if (newRefCnt == 0) {
    // It is possible for the last Release() call to happen off-main-thread.
    // If so, we need to dispatch an event to delete ourselves.
    if (NS_IsMainThread()) {
      delete this;
    } else {
      // We need to delete this object on the main thread, but we aren't on the
      // main thread right now, so we send a reference to ourselves to the main
      // thread to be re-released there.
      RefPtr<MainThreadHandoff> self = this;
      NS_ReleaseOnMainThreadSystemGroup("MainThreadHandoff", self.forget());
    }
  }
  return newRefCnt;
}

HRESULT
MainThreadHandoff::FixIServiceProvider(ICallFrame* aFrame) {
  MOZ_ASSERT(aFrame);

  CALLFRAMEPARAMINFO iidOutParamInfo;
  HRESULT hr = aFrame->GetParamInfo(1, &iidOutParamInfo);
  if (FAILED(hr)) {
    return hr;
  }

  VARIANT varIfaceOut;
  hr = aFrame->GetParam(2, &varIfaceOut);
  if (FAILED(hr)) {
    return hr;
  }

  MOZ_ASSERT(varIfaceOut.vt == (VT_UNKNOWN | VT_BYREF));
  if (varIfaceOut.vt != (VT_UNKNOWN | VT_BYREF)) {
    return DISP_E_BADVARTYPE;
  }

  IID** iidOutParam =
      reinterpret_cast<IID**>(static_cast<BYTE*>(aFrame->GetStackLocation()) +
                              iidOutParamInfo.stackOffset);

  return OnWalkInterface(**iidOutParam,
                         reinterpret_cast<void**>(varIfaceOut.ppunkVal), FALSE,
                         TRUE);
}

HRESULT
MainThreadHandoff::OnCall(ICallFrame* aFrame) {
  LogEvent logEvent;

  // (1) Get info about the method call
  HRESULT hr;
  IID iid;
  ULONG method;
  hr = aFrame->GetIIDAndMethod(&iid, &method);
  if (FAILED(hr)) {
    return hr;
  }

  RefPtr<IInterceptor> interceptor;
  hr = mInterceptor->Resolve(IID_IInterceptor,
                             (void**)getter_AddRefs(interceptor));
  if (FAILED(hr)) {
    return hr;
  }

  InterceptorTargetPtr<IUnknown> targetInterface;
  hr = interceptor->GetTargetForIID(iid, targetInterface);
  if (FAILED(hr)) {
    return hr;
  }

  // (2) Execute the method call synchronously on the main thread
  RefPtr<HandoffRunnable> handoffInfo(
      new HandoffRunnable(aFrame, targetInterface.get()));
  MainThreadInvoker invoker;
  if (!invoker.Invoke(do_AddRef(handoffInfo))) {
    MOZ_ASSERT(false);
    return E_UNEXPECTED;
  }
  hr = handoffInfo->GetResult();
  MOZ_ASSERT(SUCCEEDED(hr));
  if (FAILED(hr)) {
    return hr;
  }

  // (3) Capture *before* wrapping outputs so that the log will contain pointers
  // to the true target interface, not the wrapped ones.
  logEvent.CaptureFrame(aFrame, targetInterface.get(), invoker.GetDuration());

  // (4) Scan the function call for outparams that contain interface pointers.
  // Those will need to be wrapped with MainThreadHandoff so that they too will
  // be exeuted on the main thread.

  hr = aFrame->GetReturnValue();
  if (FAILED(hr)) {
    // If the call resulted in an error then there's not going to be anything
    // that needs to be wrapped.
    return S_OK;
  }

  if (iid == IID_IServiceProvider) {
    // The only possible method index for IID_IServiceProvider is for
    // QueryService at index 3; its other methods are inherited from IUnknown
    // and are not processed here.
    MOZ_ASSERT(method == 3);
    // (5) If our interface is IServiceProvider, we need to manually ensure
    // that the correct IID is provided for the interface outparam in
    // IServiceProvider::QueryService.
    hr = FixIServiceProvider(aFrame);
    if (FAILED(hr)) {
      return hr;
    }
  } else if (const ArrayData* arrayData = FindArrayData(iid, method)) {
    // (6) Unfortunately ICallFrame::WalkFrame does not correctly handle array
    // outparams. Instead, we find out whether anybody has called
    // mscom::RegisterArrayData to supply array parameter information and use it
    // if available. This is a terrible hack, but it works for the short term.
    // In the longer term we want to be able to use COM proxy/stub metadata to
    // resolve array information for us.
    hr = FixArrayElements(aFrame, *arrayData);
    if (FAILED(hr)) {
      return hr;
    }
  } else {
    SavedCallFrame savedFrame(WrapNotNull(aFrame));

    // (7) Scan the outputs looking for any outparam interfaces that need
    // wrapping. NB: WalkFrame does not correctly handle array outparams. It
    // processes the first element of an array but not the remaining elements
    // (if any).
    hr = aFrame->WalkFrame(CALLFRAME_WALK_OUT, this);
    if (FAILED(hr)) {
      return hr;
    }
  }

  return S_OK;
}

static PVOID ResolveArrayPtr(VARIANT& aVariant) {
  if (!(aVariant.vt & VT_BYREF)) {
    return nullptr;
  }
  return aVariant.byref;
}

static PVOID* ResolveInterfacePtr(PVOID aArrayPtr, VARTYPE aVartype,
                                  LONG aIndex) {
  if (aVartype != (VT_VARIANT | VT_BYREF)) {
    IUnknown** ifaceArray = reinterpret_cast<IUnknown**>(aArrayPtr);
    return reinterpret_cast<PVOID*>(&ifaceArray[aIndex]);
  }
  VARIANT* variantArray = reinterpret_cast<VARIANT*>(aArrayPtr);
  VARIANT& element = variantArray[aIndex];
  return &element.byref;
}

HRESULT
MainThreadHandoff::FixArrayElements(ICallFrame* aFrame,
                                    const ArrayData& aArrayData) {
  // Extract the array length
  VARIANT paramVal;
  VariantInit(&paramVal);
  HRESULT hr = aFrame->GetParam(aArrayData.mLengthParamIndex, &paramVal);
  MOZ_ASSERT(SUCCEEDED(hr) && (paramVal.vt == (VT_I4 | VT_BYREF) ||
                               paramVal.vt == (VT_UI4 | VT_BYREF)));
  if (FAILED(hr) || (paramVal.vt != (VT_I4 | VT_BYREF) &&
                     paramVal.vt != (VT_UI4 | VT_BYREF))) {
    return hr;
  }

  const LONG arrayLength = *(paramVal.plVal);
  if (!arrayLength) {
    // Nothing to do
    return S_OK;
  }

  // Extract the array parameter
  VariantInit(&paramVal);
  PVOID arrayPtr = nullptr;
  hr = aFrame->GetParam(aArrayData.mArrayParamIndex, &paramVal);
  if (hr == DISP_E_BADVARTYPE) {
    // ICallFrame::GetParam is not able to coerce the param into a VARIANT.
    // That's ok, we can try to do it ourselves.
    CALLFRAMEPARAMINFO paramInfo;
    hr = aFrame->GetParamInfo(aArrayData.mArrayParamIndex, &paramInfo);
    if (FAILED(hr)) {
      return hr;
    }
    PVOID stackBase = aFrame->GetStackLocation();
    if (aArrayData.mFlag == ArrayData::Flag::eAllocatedByServer) {
      // In order for the server to allocate the array's buffer and store it in
      // an outparam, the parameter must be typed as Type***. Since the base
      // of the array is Type*, we must dereference twice.
      arrayPtr = **reinterpret_cast<PVOID**>(
          reinterpret_cast<PBYTE>(stackBase) + paramInfo.stackOffset);
    } else {
      // We dereference because we need to obtain the value of a parameter
      // from a stack offset. This pointer is the base of the array.
      arrayPtr = *reinterpret_cast<PVOID*>(reinterpret_cast<PBYTE>(stackBase) +
                                           paramInfo.stackOffset);
    }
  } else if (FAILED(hr)) {
    return hr;
  } else {
    arrayPtr = ResolveArrayPtr(paramVal);
  }

  MOZ_ASSERT(arrayPtr);
  if (!arrayPtr) {
    return DISP_E_BADVARTYPE;
  }

  // We walk the elements of the array and invoke OnWalkInterface to wrap each
  // one, just as ICallFrame::WalkFrame would do.
  for (LONG index = 0; index < arrayLength; ++index) {
    hr = OnWalkInterface(aArrayData.mArrayParamIid,
                         ResolveInterfacePtr(arrayPtr, paramVal.vt, index),
                         FALSE, TRUE);
    if (FAILED(hr)) {
      return hr;
    }
  }
  return S_OK;
}

HRESULT
MainThreadHandoff::SetInterceptor(IWeakReference* aInterceptor) {
  mInterceptor = aInterceptor;
  return S_OK;
}

HRESULT
MainThreadHandoff::GetHandler(NotNull<CLSID*> aHandlerClsid) {
  if (!mHandlerProvider) {
    return E_NOTIMPL;
  }

  return mHandlerProvider->GetHandler(aHandlerClsid);
}

HRESULT
MainThreadHandoff::GetHandlerPayloadSize(NotNull<IInterceptor*> aInterceptor,
                                         NotNull<DWORD*> aOutPayloadSize) {
  if (!mHandlerProvider) {
    return E_NOTIMPL;
  }
  return mHandlerProvider->GetHandlerPayloadSize(aInterceptor, aOutPayloadSize);
}

HRESULT
MainThreadHandoff::WriteHandlerPayload(NotNull<IInterceptor*> aInterceptor,
                                       NotNull<IStream*> aStream) {
  if (!mHandlerProvider) {
    return E_NOTIMPL;
  }
  return mHandlerProvider->WriteHandlerPayload(aInterceptor, aStream);
}

REFIID
MainThreadHandoff::MarshalAs(REFIID aIid) {
  if (!mHandlerProvider) {
    return aIid;
  }
  return mHandlerProvider->MarshalAs(aIid);
}

HRESULT
MainThreadHandoff::DisconnectHandlerRemotes() {
  if (!mHandlerProvider) {
    return E_NOTIMPL;
  }

  return mHandlerProvider->DisconnectHandlerRemotes();
}

HRESULT
MainThreadHandoff::OnWalkInterface(REFIID aIid, PVOID* aInterface,
                                   BOOL aIsInParam, BOOL aIsOutParam) {
  MOZ_ASSERT(aInterface && aIsOutParam);
  if (!aInterface || !aIsOutParam) {
    return E_UNEXPECTED;
  }

  // Adopt aInterface for the time being. We can't touch its refcount off
  // the main thread, so we'll use STAUniquePtr so that we can safely
  // Release() it if necessary.
  STAUniquePtr<IUnknown> origInterface(static_cast<IUnknown*>(*aInterface));
  *aInterface = nullptr;

  if (!origInterface) {
    // Nothing to wrap.
    return S_OK;
  }

  // First make sure that aInterface isn't a proxy - we don't want to wrap
  // those.
  if (IsProxy(origInterface.get())) {
    *aInterface = origInterface.release();
    return S_OK;
  }

  RefPtr<IInterceptor> interceptor;
  HRESULT hr = mInterceptor->Resolve(IID_IInterceptor,
                                     (void**)getter_AddRefs(interceptor));
  MOZ_ASSERT(SUCCEEDED(hr));
  if (FAILED(hr)) {
    return hr;
  }

  // Now make sure that origInterface isn't referring to the same IUnknown
  // as an interface that we are already managing. We can determine this by
  // querying (NOT casting!) both objects for IUnknown and then comparing the
  // resulting pointers.
  InterceptorTargetPtr<IUnknown> existingTarget;
  hr = interceptor->GetTargetForIID(aIid, existingTarget);
  if (SUCCEEDED(hr)) {
    // We'll start by checking the raw pointers. If they are equal, then the
    // objects are equal. OTOH, if they differ, we must compare their
    // IUnknown pointers to know for sure.
    bool areTargetsEqual = existingTarget.get() == origInterface.get();

    if (!areTargetsEqual) {
      // This check must be done on the main thread
      auto checkFn = [&existingTarget, &origInterface,
                      &areTargetsEqual]() -> void {
        RefPtr<IUnknown> unkExisting;
        HRESULT hrExisting = existingTarget->QueryInterface(
            IID_IUnknown, (void**)getter_AddRefs(unkExisting));
        RefPtr<IUnknown> unkNew;
        HRESULT hrNew = origInterface->QueryInterface(
            IID_IUnknown, (void**)getter_AddRefs(unkNew));
        areTargetsEqual =
            SUCCEEDED(hrExisting) && SUCCEEDED(hrNew) && unkExisting == unkNew;
      };

      MainThreadInvoker invoker;
      invoker.Invoke(NS_NewRunnableFunction(
          "MainThreadHandoff::OnWalkInterface", checkFn));
    }

    if (areTargetsEqual) {
      // The existing interface and the new interface both belong to the same
      // target object. Let's just use the existing one.
      void* intercepted = nullptr;
      hr = interceptor->GetInterceptorForIID(aIid, &intercepted);
      MOZ_ASSERT(SUCCEEDED(hr));
      if (FAILED(hr)) {
        return hr;
      }
      *aInterface = intercepted;
      return S_OK;
    }
  }

  IID effectiveIid = aIid;

  RefPtr<IHandlerProvider> payload;
  if (mHandlerProvider) {
    if (aIid == IID_IUnknown) {
      const SavedCallFrame& curFrame = SavedCallFrame::Get();

      IID callIid;
      ULONG callMethod;
      hr = curFrame.GetIidAndMethod(WrapNotNull(&callIid),
                                    WrapNotNull(&callMethod));
      if (FAILED(hr)) {
        return hr;
      }

      effectiveIid =
          mHandlerProvider->GetEffectiveOutParamIid(callIid, callMethod);
    }

    hr = mHandlerProvider->NewInstance(
        effectiveIid, ToInterceptorTargetPtr(origInterface),
        WrapNotNull((IHandlerProvider**)getter_AddRefs(payload)));
    MOZ_ASSERT(SUCCEEDED(hr));
    if (FAILED(hr)) {
      return hr;
    }
  }

  // Now create a new MainThreadHandoff wrapper...
  RefPtr<IInterceptorSink> handoff;
  hr = MainThreadHandoff::Create(payload, getter_AddRefs(handoff));
  MOZ_ASSERT(SUCCEEDED(hr));
  if (FAILED(hr)) {
    return hr;
  }

  REFIID interceptorIid =
      payload ? payload->MarshalAs(effectiveIid) : effectiveIid;

  RefPtr<IUnknown> wrapped;
  hr = Interceptor::Create(std::move(origInterface), handoff, interceptorIid,
                           getter_AddRefs(wrapped));
  MOZ_ASSERT(SUCCEEDED(hr));
  if (FAILED(hr)) {
    return hr;
  }

  // And replace the original interface pointer with the wrapped one.
  wrapped.forget(reinterpret_cast<IUnknown**>(aInterface));

  return S_OK;
}

}  // namespace mscom
}  // namespace mozilla