The Tor Browser: js/xpconnect/public/nsAutoJSValHolder.h@a63d609f5ebe

     1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

     2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */

     3 /* This Source Code Form is subject to the terms of the Mozilla Public

     4  * License, v. 2.0. If a copy of the MPL was not distributed with this

     5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

     7 #ifndef __NSAUTOJSVALHOLDER_H__

     8 #define __NSAUTOJSVALHOLDER_H__

    10 #include "nsDebug.h"

    11 #include "jsapi.h"

    13 /**

    14  * Simple class that looks and acts like a JS::Value except that it unroots

    15  * itself automatically if Root() is ever called. Designed to be rooted on the

    16  * context or runtime (but not both!).

    17  */

    18 class nsAutoJSValHolder

    19 {

    20 public:

    21   nsAutoJSValHolder()

    22     : mVal(JSVAL_NULL), mRt(nullptr)

    23   {

    24     // nothing to do

    25   }

    27   /**

    28    * Always release on destruction.

    29    */

    30   virtual ~nsAutoJSValHolder() {

    31     Release();

    32   }

    34   nsAutoJSValHolder(const nsAutoJSValHolder& aOther)

    35     : mVal(JSVAL_NULL), mRt(nullptr)

    36   {

    37     *this = aOther;

    38   }

    40   nsAutoJSValHolder& operator=(const nsAutoJSValHolder& aOther) {

    41     if (this != &aOther) {

    42       if (aOther.IsHeld()) {

    43         // XXX No error handling here...

    44         this->Hold(aOther.mRt);

    45       }

    46       else {

    47         this->Release();

    48       }

    49       *this = static_cast<JS::Value>(aOther);

    50     }

    51     return *this;

    52   }

    54   /**

    55    * Hold by rooting on the context's runtime.

    56    */

    57   bool Hold(JSContext* aCx) {

    58     return Hold(JS_GetRuntime(aCx));

    59   }

    61   /**

    62    * Hold by rooting on the runtime.

    63    * Note that mVal may be JSVAL_NULL, which is not a problem.

    64    */

    65   bool Hold(JSRuntime* aRt) {

    66     MOZ_ASSERT_IF(mRt, mRt == aRt);

    68     if (!mRt && JS::AddNamedValueRootRT(aRt, &mVal, "nsAutoJSValHolder")) {

    69       mRt = aRt;

    70     }

    72     return !!mRt;

    73   }

    75   /**

    76    * Manually release, nullifying mVal, and mRt, but returning

    77    * the original JS::Value.

    78    */

    79   JS::Value Release() {

    80     JS::Value oldval = mVal;

    82     if (mRt) {

    83       JS::RemoveValueRootRT(mRt, &mVal); // infallible

    84       mRt = nullptr;

    85     }

    87     mVal = JSVAL_NULL;

    89     return oldval;

    90   }

    92   /**

    93    * Determine if Hold has been called.

    94    */

    95   bool IsHeld() const {

    96     return !!mRt;

    97   }

    99   /**

   100    * Explicit JSObject* conversion.

   101    */

   102   JSObject* ToJSObject() const {

   103     return mVal.isObject()

   104          ? &mVal.toObject()

   105          : nullptr;

   106   }

   108   /**

   109    * Pretend to be a JS::Value.

   110    */

   111   operator JS::Value() const { return mVal; }

   112   JS::Value get() const { return mVal; }

   114   nsAutoJSValHolder &operator=(JSObject* aOther) {

   115     return *this = OBJECT_TO_JSVAL(aOther);

   116   }

   118   nsAutoJSValHolder &operator=(JS::Value aOther) {

   119 #ifdef DEBUG

   120     if (JSVAL_IS_GCTHING(aOther) && !JSVAL_IS_NULL(aOther)) {

   121       MOZ_ASSERT(IsHeld(), "Not rooted!");

   122     }

   123 #endif

   124     mVal = aOther;

   125     return *this;

   126   }

   128 private:

   129   JS::Heap<JS::Value> mVal;

   130   JSRuntime* mRt;

   131 };

   133 #endif /* __NSAUTOJSVALHOLDER_H__ */

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