// Name: wx/cocoa/ObjcRef.h
// Purpose: wxObjcAutoRef template class
// Author: David Elliott
-// Modified by:
+// Modified by:
// Created: 2004/03/28
// RCS-ID: $Id$
// Copyright: (c) 2004 David Elliott <dfe@cox.net>
#ifndef _WX_COCOA_OBJCREF_H__
#define _WX_COCOA_OBJCREF_H__
+
+// Reuse wxCFRef-related code (e.g. wxCFRetain/wxCFRelease)
+#include "wx/osx/core/cfref.h"
+
+// NOTE WELL: We can only know whether or not GC can be used when compiling Objective-C.
+// Therefore we cannot implement these functions except when compiling Objective-C.
+#ifdef __OBJC__
+/*! @function wxGCSafeRetain
+ @templatefield Type (implicit) An Objective-C class type
+ @arg r Pointer to Objective-C object. May be null.
+ @abstract Retains the Objective-C object, even when using Apple's garbage collector
+ @discussion
+ When Apple's garbage collector is enabled, the usual [obj retain] and [obj release] messages
+ are ignored. Instead the collector with help from compiler-generated write-barriers tracks
+ reachable objects. The write-barriers are generated when setting i-vars of C++ classes but
+ they are ignored by the garbage collector unless the C++ object is in GC-managed memory.
+
+ The simple solution is to use CFRetain on the Objective-C object which has been enhanced in
+ GC mode to forcibly retain the object. In Retain/Release (RR) mode the CFRetain function has
+ the same effect as [obj retain]. Note that GC vs. RR is selected at runtime.
+
+ Take care that wxGCSafeRetain must be balanced with wxGCSafeRelease and that conversely
+ wxGCSafeRelease must only be called on objects to balance wxGCSafeRetain. In particular when
+ receiving an Objective-C object from an alloc or copy method take care that you must retain
+ it with wxGCSafeRetain and balance the initial alloc with a standard release.
+
+ Example:
+ wxGCSafeRelease(m_obj); // release current object (if any)
+ NSObject *obj = [[NSObject alloc] init];
+ m_obj = wxGCSafeRetain(obj);
+ [obj release];
+
+ Alternatively (same effect, perhaps less clear):
+ wxGCSafeRelease(m_obj); // release current object (if any)
+ m_obj = wxGCSafeRetain([[NSObject alloc] init]);
+ [m_obj release]; // balance alloc
+
+ Consider the effect on the retain count from each statement (alloc, CFRetain, release)
+ In RR mode: retainCount = 1, +1, -1
+ In GC mode: strongRetainCount = 0, +1, -0
+
+ This is a template function to ensure it is used on raw pointers and never on pointer-holder
+ objects via implicit conversion operators.
+*/
+template <class Type>
+inline Type * wxGCSafeRetain(Type *r)
+{
+#ifdef __OBJC_GC__
+ return static_cast<Type*>(wxCFRetain(r));
+#else
+ return [r retain];
+#endif
+}
+
+/*! @function wxGCSafeRelease
+ @templatefield Type (implicit) An Objective-C class type
+ @arg r Pointer to Objective-C object. May be null.
+ @abstract Balances wxGCSafeRetain. Particularly useful with the Apple Garbage Collector.
+ @discussion
+ See the wxGCSafeRetain documentation for more details.
+
+ Example (from wxGCSafeRetain documentation):
+ wxGCSafeRelease(m_obj); // release current object (if any)
+ m_obj = wxGCSafeRetain([[NSObject alloc] init]);
+ [m_obj release]; // balance alloc
+
+ When viewed from the start, m_obj ought to start as nil. However, the second time through
+ the wxGCSafeRelease call becomes critical as it releases the retain from the first time
+ through.
+
+ In the destructor for this C++ object with the m_obj i-var you ought to do the following:
+ wxGCSafeRelease(m_obj);
+ m_obj = nil; // Not strictly needed, but safer.
+
+ Under no circumstances should you balance an alloc or copy with a wxGCSafeRelease.
+*/
+template <class Type>
+inline void wxGCSafeRelease(Type *r)
+{
+#ifdef __OBJC_GC__
+ wxCFRelease(r);
+#else
+ [r release];
+#endif
+}
+#else
+// NOTE: When not compiling Objective-C, declare these functions such that they can be
+// used by other inline-implemented methods. Since those methods in turn will not actually
+// be used from non-ObjC code the compiler ought not emit them. If it emits an out of
+// line copy of those methods then presumably it will have also emitted at least one
+// out of line copy of these functions from at least one Objective-C++ translation unit.
+// That means the out of line implementation will be available at link time.
+
+template <class Type>
+inline Type * wxGCSafeRetain(Type *r);
+
+template <class Type>
+inline void wxGCSafeRelease(Type *r);
+
+#endif //def __OBJC__
+
/*
wxObjcAutoRefFromAlloc: construct a reference to an object that was
[NSObject -alloc]'ed and thus does not need a retain
class wxObjcAutoRefBase
{
protected:
+ /*! @function ObjcRetain
+ @abstract Simply does [p retain].
+ */
static struct objc_object* ObjcRetain(struct objc_object*);
+
+ /*! @function ObjcRelease
+ @abstract Simply does [p release].
+ */
static void ObjcRelease(struct objc_object*);
};
-// T should be a pointer like NSObject*
+/*! @class wxObjcAutoRefFromAlloc
+ @templatefield T The type of _pointer_ (e.g. NSString*, NSRunLoop*)
+ @abstract Pointer-holder for Objective-C objects
+ @discussion
+ When constructing this object from a raw pointer, the pointer is assumed to have
+ come from an alloc-style method. That is, once you construct this object from
+ the pointer you must not balance your alloc with a call to release.
+
+ This class has been carefully designed to work with both the traditional Retain/Release
+ and the new Garbage Collected modes. In RR-mode it will prevent the object from being
+ released by managing the reference count using the retain/release semantics. In GC-mode
+ it will use a method (currently CFRetain/CFRelease) to ensure the object will never be
+ finalized until this object is destroyed.
+ */
template <class T>
class wxObjcAutoRefFromAlloc: wxObjcAutoRefBase
wxObjcAutoRefFromAlloc(T p = 0)
: m_ptr(p)
// NOTE: this is from alloc. Do NOT retain
- {}
+ {
+ // CFRetain
+ // GC: Object is strongly retained and prevented from being collected
+ // non-GC: Simply realizes it's an Objective-C object and calls [p retain]
+ wxGCSafeRetain(p);
+ // ObjcRelease (e.g. [p release])
+ // GC: Objective-C retain/release mean nothing in GC mode
+ // non-GC: This is a normal release call, balancing the retain
+ ObjcRelease(static_cast<T>(p));
+ // The overall result:
+ // GC: Object is strongly retained
+ // non-GC: Retain count is the same as it was (retain then release)
+ }
wxObjcAutoRefFromAlloc(const wxObjcAutoRefFromAlloc& otherRef)
: m_ptr(otherRef.m_ptr)
- { ObjcRetain(m_ptr); }
+ { wxGCSafeRetain(m_ptr); }
~wxObjcAutoRefFromAlloc()
- { ObjcRelease(m_ptr); }
+ { wxGCSafeRelease(m_ptr); }
wxObjcAutoRefFromAlloc& operator=(const wxObjcAutoRefFromAlloc& otherRef)
- { ObjcRetain(otherRef.m_ptr);
- ObjcRelease(m_ptr);
+ { wxGCSafeRetain(otherRef.m_ptr);
+ wxGCSafeRelease(m_ptr);
m_ptr = otherRef.m_ptr;
return *this;
}
operator T() const
- { return m_ptr; }
+ { return static_cast<T>(m_ptr); }
T operator->() const
- { return m_ptr; }
+ { return static_cast<T>(m_ptr); }
protected:
- T m_ptr;
+ /*! @field m_ptr The pointer to the Objective-C object
+ @discussion
+ The pointer to the Objective-C object is typed as void* to avoid compiler-generated write
+ barriers as would be used for implicitly __strong object pointers and to avoid the similar
+ read barriers as would be used for an explicitly __weak object pointer. The write barriers
+ are useless unless this object is located in GC-managed heap which is highly unlikely.
+
+ Since we guarantee strong reference via CFRetain/CFRelease the write-barriers are not needed
+ at all, even if this object does happen to be allocated in GC-managed heap.
+ */
+ void *m_ptr;
};
-// The only thing wxObjcAutoRef has to do is retain an initial object
+/*!
+ @class wxObjcAutoRef
+ @description
+ A pointer holder that does retain its argument.
+ NOTE: It is suggest that you instead use wxObjcAutoRefFromAlloc<T> foo([aRawPointer retain])
+ */
template <class T>
class wxObjcAutoRef: public wxObjcAutoRefFromAlloc<T>
{
public:
+ /*! @method wxObjcAutoRef
+ @description
+ Uses the underlying wxObjcAutoRefFromAlloc and simply does a typical [p retain] such that
+ in RR-mode the object is in effectively the same retain-count state as it would have been
+ coming straight from an alloc method.
+ */
wxObjcAutoRef(T p = 0)
: wxObjcAutoRefFromAlloc<T>(p)
- { ObjcRetain(m_ptr); }
+ { // NOTE: ObjcRetain is correct because in GC-mode it balances ObjcRelease in our superclass constructor
+ // In RR mode it does retain and the superclass does retain/release thus resulting in an overall retain.
+ ObjcRetain(static_cast<T>(wxObjcAutoRefFromAlloc<T>::m_ptr));
+ }
~wxObjcAutoRef() {}
wxObjcAutoRef(const wxObjcAutoRef& otherRef)
: wxObjcAutoRefFromAlloc<T>(otherRef)
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