Objective-C API: Need a good way to reference event handlers without causing cycles
https://bugs.webkit.org/show_bug.cgi?id=111088

Reviewed by Geoffrey Garen.

JSManagedValue is like a special kind of weak value. When you create a JSManagedValue, you can
supply an Objective-C object as its "owner". As long as the Objective-C owner object remains
alive and its wrapper remains accessible to the JSC garbage collector (e.g. by being marked by 
the global object), the reference to the JavaScript value is strong. As soon as the Objective-C
owner is deallocated or its wrapper becomes inaccessible to the garbage collector, the reference
becomes weak.

If you do not supply an owner or you use the weakValueWithValue: convenience class method, the
returned JSManagedValue behaves as a normal weak reference.

This new class allows clients to maintain references to JavaScript values in the Objective-C
heap without creating reference cycles/leaking memory.

* API/JSAPIWrapperObject.cpp: Added.
(JSC):
(JSC::::createStructure):
(JSC::JSAPIWrapperObject::JSAPIWrapperObject): This is a special JSObject for the Objective-C API that knows
for the purposes of garbage collection/marking that it wraps an opaque Objective-C object.
(JSC::JSAPIWrapperObject::visitChildren): We add the pointer to the wrapped Objective-C object to the set of
opaque roots so that the weak handle owner for JSManagedValues can find it later.
* API/JSAPIWrapperObject.h: Added.
(JSC):
(JSAPIWrapperObject):
(JSC::JSAPIWrapperObject::wrappedObject):
(JSC::JSAPIWrapperObject::setWrappedObject):
* API/JSBase.cpp:
(JSSynchronousGarbageCollect):
* API/JSBasePrivate.h:
* API/JSCallbackObject.cpp:
(JSC):
* API/JSCallbackObject.h:
(JSC::JSCallbackObject::destroy): Moved this to the header so that we don't get link errors with JSAPIWrapperObject.
* API/JSContext.mm:
(-[JSContext initWithVirtualMachine:]): We weren't adding manually allocated/initialized JSVirtualMachine objects to 
the global cache of virtual machines. The init methods handle this now rather than contextWithGlobalContextRef, since 
not everyone is guaranteed to use the latter.
(-[JSContext initWithGlobalContextRef:]):
(+[JSContext contextWithGlobalContextRef:]):
* API/JSManagedValue.h: Added.
* API/JSManagedValue.mm: Added.
(JSManagedValueHandleOwner):
(managedValueHandleOwner):
(+[JSManagedValue weakValueWithValue:]):
(+[JSManagedValue managedValueWithValue:owner:]):
(-[JSManagedValue init]): We explicitly call the ARC entrypoints to initialize/get the weak owner field since we don't 
use ARC when building our framework.
(-[JSManagedValue initWithValue:]):
(-[JSManagedValue initWithValue:owner:]):
(-[JSManagedValue dealloc]):
(-[JSManagedValue value]):
(-[JSManagedValue weakOwner]):
(JSManagedValueHandleOwner::isReachableFromOpaqueRoots): If the Objective-C owner is still alive (i.e. loading the weak field
returns non-nil) and that value was added to the set of opaque roots by the wrapper for that Objective-C owner, then the the 
JSObject to which the JSManagedObject refers is still alive.
* API/JSObjectRef.cpp: We have to add explicit checks for the JSAPIWrapperObject, just like the other types of JSCallbackObjects.
(JSObjectGetPrivate):
(JSObjectSetPrivate):
(JSObjectGetPrivateProperty):
(JSObjectSetPrivateProperty):
(JSObjectDeletePrivateProperty):
* API/JSValue.mm:
(objectToValueWithoutCopy):
* API/JSValueRef.cpp:
(JSValueIsObjectOfClass):
* API/JSVirtualMachine.mm:
(-[JSVirtualMachine initWithContextGroupRef:]):
(+[JSVirtualMachine virtualMachineWithContextGroupRef:]):
* API/JSWrapperMap.mm:
(wrapperFinalize):
(makeWrapper): This is our own internal version of JSObjectMake which creates JSAPIWrapperObjects, the Obj-C API 
version of JSCallbackObjects.
(createObjectWithCustomBrand):
(-[JSObjCClassInfo wrapperForObject:]):
(tryUnwrapObjcObject):
* API/JavaScriptCore.h:
* API/tests/testapi.mm: Added new tests for the strong and weak uses of JSManagedValue in the context of an 
onclick handler for an Objective-C object inserted into a JSContext.
(-[TextXYZ setWeakOnclick:]):
(-[TextXYZ setOnclick:]):
(-[TextXYZ weakOnclick]):
(-[TextXYZ onclick]):
(-[TextXYZ click]):
* CMakeLists.txt: Various build system additions.
* GNUmakefile.list.am:
* JavaScriptCore.gypi:
* JavaScriptCore.vcproj/JavaScriptCore/JavaScriptCore.vcproj:
* JavaScriptCore.xcodeproj/project.pbxproj:
* runtime/JSGlobalObject.cpp: Added the new canonical Structure for the JSAPIWrapperObject class.
(JSC::JSGlobalObject::reset):
(JSC):
(JSC::JSGlobalObject::visitChildren):
* runtime/JSGlobalObject.h:
(JSGlobalObject):
(JSC::JSGlobalObject::objcWrapperObjectStructure):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145119 268f45cc-cd09-0410-ab3c-d52691b4dbfc