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.

Implementation

Mercurial (777e60ca8853)

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
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* 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/. */

/**
 * A common base class for representing WebIDL callback function and
 * callback interface types in C++.
 *
 * This class implements common functionality like lifetime
 * management, initialization with the JS object, and setup of the
 * call environment.  Subclasses are responsible for providing methods
 * that do the call into JS as needed.
 */

#ifndef mozilla_dom_CallbackObject_h
#define mozilla_dom_CallbackObject_h

#include "nsISupports.h"
#include "nsISupportsImpl.h"
#include "nsCycleCollectionParticipant.h"
#include "jswrapper.h"
#include "mozilla/Assertions.h"
#include "mozilla/ErrorResult.h"
#include "mozilla/HoldDropJSObjects.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/dom/ScriptSettings.h"
#include "nsContentUtils.h"
#include "nsWrapperCache.h"
#include "nsJSEnvironment.h"
#include "xpcpublic.h"

namespace mozilla {
namespace dom {

#define DOM_CALLBACKOBJECT_IID \
{ 0xbe74c190, 0x6d76, 0x4991, \
 { 0x84, 0xb9, 0x65, 0x06, 0x99, 0xe6, 0x93, 0x2b } }

class CallbackObject : public nsISupports
{
public:
  NS_DECLARE_STATIC_IID_ACCESSOR(DOM_CALLBACKOBJECT_IID)

  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(CallbackObject)

  // The caller may pass a global object which will act as an override for the
  // incumbent script settings object when the callback is invoked (overriding
  // the entry point computed from aCallback). If no override is required, the
  // caller should pass null.
  explicit CallbackObject(JS::Handle<JSObject*> aCallback, nsIGlobalObject *aIncumbentGlobal)
  {
    Init(aCallback, aIncumbentGlobal);
  }

  virtual ~CallbackObject()
  {
    DropJSObjects();
  }

  JS::Handle<JSObject*> Callback() const
  {
    JS::ExposeObjectToActiveJS(mCallback);
    return CallbackPreserveColor();
  }

  /*
   * This getter does not change the color of the JSObject meaning that the
   * object returned is not guaranteed to be kept alive past the next CC.
   *
   * This should only be called if you are certain that the return value won't
   * be passed into a JS API function and that it won't be stored without being
   * rooted (or otherwise signaling the stored value to the CC).
   */
  JS::Handle<JSObject*> CallbackPreserveColor() const
  {
    // Calling fromMarkedLocation() is safe because we trace our mCallback, and
    // because the value of mCallback cannot change after if has been set.
    return JS::Handle<JSObject*>::fromMarkedLocation(mCallback.address());
  }

  nsIGlobalObject* IncumbentGlobalOrNull() const
  {
    return mIncumbentGlobal;
  }

  enum ExceptionHandling {
    // Report any exception and don't throw it to the caller code.
    eReportExceptions,
    // Throw an exception to the caller code if the thrown exception is a
    // binding object for a DOMError from the caller's scope, otherwise report
    // it.
    eRethrowContentExceptions,
    // Throw any exception to the caller code.
    eRethrowExceptions
  };

  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
  {
    return aMallocSizeOf(this);
  }

protected:
  explicit CallbackObject(CallbackObject* aCallbackObject)
  {
    Init(aCallbackObject->mCallback, aCallbackObject->mIncumbentGlobal);
  }

  bool operator==(const CallbackObject& aOther) const
  {
    JSObject* thisObj =
      js::UncheckedUnwrap(CallbackPreserveColor());
    JSObject* otherObj =
      js::UncheckedUnwrap(aOther.CallbackPreserveColor());
    return thisObj == otherObj;
  }

private:
  inline void Init(JSObject* aCallback, nsIGlobalObject* aIncumbentGlobal)
  {
    MOZ_ASSERT(aCallback && !mCallback);
    // Set script objects before we hold, on the off chance that a GC could
    // somehow happen in there... (which would be pretty odd, granted).
    mCallback = aCallback;
    if (aIncumbentGlobal) {
      mIncumbentGlobal = aIncumbentGlobal;
      mIncumbentJSGlobal = aIncumbentGlobal->GetGlobalJSObject();
    }
    mozilla::HoldJSObjects(this);
  }

  CallbackObject(const CallbackObject&) MOZ_DELETE;
  CallbackObject& operator =(const CallbackObject&) MOZ_DELETE;

protected:
  void DropJSObjects()
  {
    MOZ_ASSERT_IF(mIncumbentJSGlobal, mCallback);
    if (mCallback) {
      mCallback = nullptr;
      mIncumbentJSGlobal = nullptr;
      mozilla::DropJSObjects(this);
    }
  }

  JS::Heap<JSObject*> mCallback;
  // Ideally, we'd just hold a reference to the nsIGlobalObject, since that's
  // what we need to pass to AutoIncumbentScript. Unfortunately, that doesn't
  // hold the actual JS global alive. So we maintain an additional pointer to
  // the JS global itself so that we can trace it.
  //
  // At some point we should consider trying to make native globals hold their
  // scripted global alive, at which point we can get rid of the duplication
  // here.
  nsCOMPtr<nsIGlobalObject> mIncumbentGlobal;
  JS::TenuredHeap<JSObject*> mIncumbentJSGlobal;

  class MOZ_STACK_CLASS CallSetup
  {
    /**
     * A class that performs whatever setup we need to safely make a
     * call while this class is on the stack, After the constructor
     * returns, the call is safe to make if GetContext() returns
     * non-null.
     */
  public:
    // If aExceptionHandling == eRethrowContentExceptions then aCompartment
    // needs to be set to the compartment in which exceptions will be rethrown.
    CallSetup(CallbackObject* aCallback, ErrorResult& aRv,
              ExceptionHandling aExceptionHandling,
              JSCompartment* aCompartment = nullptr,
              bool aIsJSImplementedWebIDL = false);
    ~CallSetup();

    JSContext* GetContext() const
    {
      return mCx;
    }

  private:
    // We better not get copy-constructed
    CallSetup(const CallSetup&) MOZ_DELETE;

    bool ShouldRethrowException(JS::Handle<JS::Value> aException);

    // Members which can go away whenever
    JSContext* mCx;

    // Caller's compartment. This will only have a sensible value if
    // mExceptionHandling == eRethrowContentExceptions.
    JSCompartment* mCompartment;

    // And now members whose construction/destruction order we need to control.
    Maybe<AutoEntryScript> mAutoEntryScript;
    Maybe<AutoIncumbentScript> mAutoIncumbentScript;

    // Constructed the rooter within the scope of mCxPusher above, so that it's
    // always within a request during its lifetime.
    Maybe<JS::Rooted<JSObject*> > mRootedCallable;

    // Can't construct a JSAutoCompartment without a JSContext either.  Also,
    // Put mAc after mAutoEntryScript so that we exit the compartment before
    // we pop the JSContext. Though in practice we'll often manually order
    // those two things.
    Maybe<JSAutoCompartment> mAc;

    // An ErrorResult to possibly re-throw exceptions on and whether
    // we should re-throw them.
    ErrorResult& mErrorResult;
    const ExceptionHandling mExceptionHandling;
    JS::ContextOptions mSavedJSContextOptions;
    const bool mIsMainThread;
  };
};

template<class WebIDLCallbackT, class XPCOMCallbackT>
class CallbackObjectHolder;

template<class T, class U>
void ImplCycleCollectionUnlink(CallbackObjectHolder<T, U>& aField);

class CallbackObjectHolderBase
{
protected:
  // Returns null on all failures
  already_AddRefed<nsISupports> ToXPCOMCallback(CallbackObject* aCallback,
                                                const nsIID& aIID) const;
};

template<class WebIDLCallbackT, class XPCOMCallbackT>
class CallbackObjectHolder : CallbackObjectHolderBase
{
  /**
   * A class which stores either a WebIDLCallbackT* or an XPCOMCallbackT*.  Both
   * types must inherit from nsISupports.  The pointer that's stored can be
   * null.
   *
   * When storing a WebIDLCallbackT*, mPtrBits is set to the pointer value.
   * When storing an XPCOMCallbackT*, mPtrBits is the pointer value with low bit
   * set.
   */
public:
  explicit CallbackObjectHolder(WebIDLCallbackT* aCallback)
    : mPtrBits(reinterpret_cast<uintptr_t>(aCallback))
  {
    NS_IF_ADDREF(aCallback);
  }

  explicit CallbackObjectHolder(XPCOMCallbackT* aCallback)
    : mPtrBits(reinterpret_cast<uintptr_t>(aCallback) | XPCOMCallbackFlag)
  {
    NS_IF_ADDREF(aCallback);
  }

  explicit CallbackObjectHolder(const CallbackObjectHolder& aOther)
    : mPtrBits(aOther.mPtrBits)
  {
    NS_IF_ADDREF(GetISupports());
  }

  CallbackObjectHolder()
    : mPtrBits(0)
  {}

  ~CallbackObjectHolder()
  {
    UnlinkSelf();
  }

  void operator=(WebIDLCallbackT* aCallback)
  {
    UnlinkSelf();
    mPtrBits = reinterpret_cast<uintptr_t>(aCallback);
    NS_IF_ADDREF(aCallback);
  }

  void operator=(XPCOMCallbackT* aCallback)
  {
    UnlinkSelf();
    mPtrBits = reinterpret_cast<uintptr_t>(aCallback) | XPCOMCallbackFlag;
    NS_IF_ADDREF(aCallback);
  }

  void operator=(const CallbackObjectHolder& aOther)
  {
    UnlinkSelf();
    mPtrBits = aOther.mPtrBits;
    NS_IF_ADDREF(GetISupports());
  }

  nsISupports* GetISupports() const
  {
    return reinterpret_cast<nsISupports*>(mPtrBits & ~XPCOMCallbackFlag);
  }

  // Boolean conversion operator so people can use this in boolean tests
  operator bool() const
  {
    return GetISupports();
  }

  // Even if HasWebIDLCallback returns true, GetWebIDLCallback() might still
  // return null.
  bool HasWebIDLCallback() const
  {
    return !(mPtrBits & XPCOMCallbackFlag);
  }

  WebIDLCallbackT* GetWebIDLCallback() const
  {
    MOZ_ASSERT(HasWebIDLCallback());
    return reinterpret_cast<WebIDLCallbackT*>(mPtrBits);
  }

  XPCOMCallbackT* GetXPCOMCallback() const
  {
    MOZ_ASSERT(!HasWebIDLCallback());
    return reinterpret_cast<XPCOMCallbackT*>(mPtrBits & ~XPCOMCallbackFlag);
  }

  bool operator==(WebIDLCallbackT* aOtherCallback) const
  {
    if (!aOtherCallback) {
      // If other is null, then we must be null to be equal.
      return !GetISupports();
    }

    if (!HasWebIDLCallback() || !GetWebIDLCallback()) {
      // If other is non-null, then we can't be equal if we have a
      // non-WebIDL callback or a null callback.
      return false;
    }

    return *GetWebIDLCallback() == *aOtherCallback;
  }

  bool operator==(XPCOMCallbackT* aOtherCallback) const
  {
    return (!aOtherCallback && !GetISupports()) ||
      (!HasWebIDLCallback() && GetXPCOMCallback() == aOtherCallback);
  }

  bool operator==(const CallbackObjectHolder& aOtherCallback) const
  {
    if (aOtherCallback.HasWebIDLCallback()) {
      return *this == aOtherCallback.GetWebIDLCallback();
    }

    return *this == aOtherCallback.GetXPCOMCallback();
  }

  // Try to return an XPCOMCallbackT version of this object.
  already_AddRefed<XPCOMCallbackT> ToXPCOMCallback() const
  {
    if (!HasWebIDLCallback()) {
      nsRefPtr<XPCOMCallbackT> callback = GetXPCOMCallback();
      return callback.forget();
    }

    nsCOMPtr<nsISupports> supp =
      CallbackObjectHolderBase::ToXPCOMCallback(GetWebIDLCallback(),
                                                NS_GET_TEMPLATE_IID(XPCOMCallbackT));
    // ToXPCOMCallback already did the right QI for us.
    return supp.forget().downcast<XPCOMCallbackT>();
  }

  // Try to return a WebIDLCallbackT version of this object.
  already_AddRefed<WebIDLCallbackT> ToWebIDLCallback() const
  {
    if (HasWebIDLCallback()) {
      nsRefPtr<WebIDLCallbackT> callback = GetWebIDLCallback();
      return callback.forget();
    }
    return nullptr;
  }

private:
  static const uintptr_t XPCOMCallbackFlag = 1u;

  friend void
  ImplCycleCollectionUnlink<WebIDLCallbackT,
                            XPCOMCallbackT>(CallbackObjectHolder& aField);

  void UnlinkSelf()
  {
    // NS_IF_RELEASE because we might have been unlinked before
    nsISupports* ptr = GetISupports();
    NS_IF_RELEASE(ptr);
    mPtrBits = 0;
  }

  uintptr_t mPtrBits;
};

NS_DEFINE_STATIC_IID_ACCESSOR(CallbackObject, DOM_CALLBACKOBJECT_IID)

template<class T, class U>
inline void
ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
                            CallbackObjectHolder<T, U>& aField,
                            const char* aName,
                            uint32_t aFlags = 0)
{
  CycleCollectionNoteChild(aCallback, aField.GetISupports(), aName, aFlags);
}

template<class T, class U>
void
ImplCycleCollectionUnlink(CallbackObjectHolder<T, U>& aField)
{
  aField.UnlinkSelf();
}

} // namespace dom
} // namespace mozilla

#endif // mozilla_dom_CallbackObject_h