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 /* -*- 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/. */

 #ifndef nsCxPusher_h

 #define nsCxPusher_h

 #include "jsapi.h"

 #include "mozilla/Maybe.h"

 #include "nsCOMPtr.h"

 namespace mozilla {

 namespace dom {

 class EventTarget;

 }

 }

 class nsIScriptContext;

 namespace mozilla {

 /**

  * Fundamental cx pushing class. All other cx pushing classes are implemented

  * in terms of this class.

  */

 class MOZ_STACK_CLASS AutoCxPusher

 {

 public:

   AutoCxPusher(JSContext *aCx, bool aAllowNull = false);

   // XPCShell uses an nsCxPusher, which contains an AutoCxPusher.

   ~AutoCxPusher();

   nsIScriptContext* GetScriptContext() { return mScx; }

   // Returns true if this AutoCxPusher performed the push that is currently at

   // the top of the cx stack.

   bool IsStackTop();

 private:

   mozilla::Maybe<JSAutoRequest> mAutoRequest;

   mozilla::Maybe<JSAutoCompartment> mAutoCompartment;

   nsCOMPtr<nsIScriptContext> mScx;

   uint32_t mStackDepthAfterPush;

 #ifdef DEBUG

   JSContext* mPushedContext;

   unsigned mCompartmentDepthOnEntry;

 #endif

 };

 } /* namespace mozilla */

 /**

  * Legacy cx pushing class.

  *

  * This class provides a rather wonky interface, with the following quirks:

  *   * The constructor is a no-op, and callers must explicitly call one of

  *     the Push() methods.

  *   * Null must be pushed with PushNull().

  *   * The cx pusher can be reused multiple times with RePush().

  *

  * This class implements this interface in terms of the much simpler

  * AutoCxPusher class below.

  */

 class MOZ_STACK_CLASS nsCxPusher

 {

 public:

   // Returns false if something erroneous happened.

   bool Push(mozilla::dom::EventTarget *aCurrentTarget);

   // If nothing has been pushed to stack, this works like Push.

   // Otherwise if context will change, Pop and Push will be called.

   bool RePush(mozilla::dom::EventTarget *aCurrentTarget);

   // If a null JSContext is passed to Push(), that will cause no

   // push to happen and false to be returned.

   void Push(JSContext *cx);

   // Explicitly push a null JSContext on the the stack

   void PushNull();

   // Pop() will be a no-op if Push() or PushNull() fail

   void Pop();

   nsIScriptContext* GetCurrentScriptContext() {

     return mPusher.empty() ? nullptr : mPusher.ref().GetScriptContext();

   }

 private:

   mozilla::Maybe<mozilla::AutoCxPusher> mPusher;

 };

 namespace mozilla {

 /**

  * Use AutoJSContext when you need a JS context on the stack but don't have one

  * passed as a parameter. AutoJSContext will take care of finding the most

  * appropriate JS context and release it when leaving the stack.

  */

 class MOZ_STACK_CLASS AutoJSContext {

 public:

   AutoJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM);

   operator JSContext*() const;

 protected:

   AutoJSContext(bool aSafe MOZ_GUARD_OBJECT_NOTIFIER_PARAM);

   // We need this Init() method because we can't use delegating constructor for

   // the moment. It is a C++11 feature and we do not require C++11 to be

   // supported to be able to compile Gecko.

   void Init(bool aSafe MOZ_GUARD_OBJECT_NOTIFIER_PARAM);

   JSContext* mCx;

   Maybe<AutoCxPusher> mPusher;

   MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER

 };

 /**

  * Use ThreadsafeAutoJSContext when you want an AutoJSContext but might be

  * running on a worker thread.

  */

 class MOZ_STACK_CLASS ThreadsafeAutoJSContext {

 public:

   ThreadsafeAutoJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM);

   operator JSContext*() const;

 private:

   JSContext* mCx; // Used on workers.  Null means mainthread.

   Maybe<JSAutoRequest> mRequest; // Used on workers.

   Maybe<AutoJSContext> mAutoJSContext; // Used on main thread.

   MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER

 };

 /**

  * AutoSafeJSContext is similar to AutoJSContext but will only return the safe

  * JS context. That means it will never call ::GetCurrentJSContext().

  */

 class MOZ_STACK_CLASS AutoSafeJSContext : public AutoJSContext {

 public:

   AutoSafeJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM);

 private:

   JSAutoCompartment mAc;

 };

 /**

  * Like AutoSafeJSContext but can be used safely on worker threads.

  */

 class MOZ_STACK_CLASS ThreadsafeAutoSafeJSContext {

 public:

   ThreadsafeAutoSafeJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM);

   operator JSContext*() const;

 private:

   JSContext* mCx; // Used on workers.  Null means mainthread.

   Maybe<JSAutoRequest> mRequest; // Used on workers.

   Maybe<AutoSafeJSContext> mAutoSafeJSContext; // Used on main thread.

   MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER

 };

 /**

  * Use AutoPushJSContext when you want to use a specific JSContext that may or

  * may not be already on the stack. This differs from nsCxPusher in that it only

  * pushes in the case that the given cx is not the active cx on the JSContext

  * stack, which avoids an expensive JS_SaveFrameChain in the common case.

  *

  * Most consumers of this should probably just use AutoJSContext. But the goal

  * here is to preserve the existing behavior while ensure proper cx-stack

  * semantics in edge cases where the context being used doesn't match the active

  * context.

  *

  * NB: This will not push a null cx even if aCx is null. Make sure you know what

  * you're doing.

  */

 class MOZ_STACK_CLASS AutoPushJSContext {

   Maybe<AutoCxPusher> mPusher;

   JSContext* mCx;

 public:

   AutoPushJSContext(JSContext* aCx);

   operator JSContext*() { return mCx; }

 };

 } // namespace mozilla

 #endif /* nsCxPusher_h */