libkern/libkern/c++/OSObject.h

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
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  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
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  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28 /*
  29 Copyright (c) 1998 Apple Computer, Inc.  All rights reserved.
  30 HISTORY
  31     1998-10-30  Godfrey van der Linden(gvdl)
  32         Created
  33 */
  34 #ifndef _LIBKERN_OSOBJECT_H
  35 #define _LIBKERN_OSOBJECT_H
  36
  37 #include <libkern/c++/OSMetaClass.h>
  38
  39 class OSSymbol;
  40 class OSString;
  41 /*!
  42     @class OSObject : OSMetaClassBase
  43     @abstract The root base class for Mac OS X kernel and just generally all-round useful class to have around.
  44     @discussion
  45 Defines the minimum functionality that an object can expect.  Implements reference counting, type safe object casting, allocation primitives & serialisation among other functionality.  This object is an abstract base class and can not be copied, nor can it be constructed by itself.
  46
  47 <br><br> Construction <br><br>
  48
  49 As Mac OS X's C++ is based upon Embedded C++ we have a problem with the typical C++ method of using constructors.  Embedded C++ does not allow exceptions.  This means that the standard constructors can not report a failure.  Well obviously initialisation of a new object can fail so we have had to work around this language limitation.  In the Mac OS X kernel we have chosen to break object construction into two phases.  Phase one is the familiar C++ new operator, the only initialisation is the object has exactly one reference after creation.  Once the new is called the client MUST call init and check it's return value.  If the init call fails then the object MUST be immediately released.  IOKit usually implements factory methods to make construction a one step process for clients.
  50
  51 <br><br>Reference Counting<br><br>
  52
  53 OSObject provides reference counting services using the $link retain(), $link release(), $link release(int when) and $link free() functions.  The public interface to the reference counting is retain() & release().  release() is implemented as a simple call to release(1).  The actual implementation of release(when) is a little subtle.  If the current reference count is less than or equal to the 'when' parameter the object will call free on itself.
  54 <br>
  55 In general a subclass is expected to only override $link free().  It may also choose to override release() if the object has a circular retain count, see $link release(int when);
  56
  57 <br><br>Runtime Type Information System<br><br>
  58
  59 The Mac OS X C++ implements a basic runtime type information system using meta class information and a number of macros, $link OSDynamicCast, $link OSTypeID, $link OSTypeIDInst, $link OSCheckTypeInst and $link OSMetaClass.
  60 */
  61 class OSObject : public OSMetaClassBase
  62 {
  63     OSDeclareAbstractStructors(OSObject)
  64
  65 private:
  66 /*! @var retainCount Number of references held on this instance. */
  67     mutable int retainCount;
  68
  69 protected:
  70
  71 /*! @function release
  72     @abstract untagged release(when) mechansim.
  73     @param when Pass through to taggedRelease. */
  74     virtual void release(int when) const;
  75
  76 /*! @function taggedRelease
  77     @abstract Primary implementation of the tagged release mechanism.
  78     @discussion  If $link retainCount <= the when argument then call $link free().  This indirect implementation of $link release allows the developer to break reference circularity.  An example of this sort of problem is a parent/child mutual reference, either the parent or child can implement: void taggedRelease(tag) { taggedRelease(tag, 2); } thus breaking the cirularity.
  79     @param when If retainCount == when then call free(). */
  80     virtual void taggedRelease(const void *tag, const int when) const;
  81
  82 /*! @function init
  83     @abstract Mac OS X kernel's primary mechanism for constructing objects.
  84     @discussion Your responsibility as a subclass author is to override the init method of your parent.  In general most of our implementations call <super>::init() before doing local initialisation, if the parent fails then return false immediately.  If you have a failure during you local initialisation then return false.
  85     @result OSObject::init Always returns true, but subclasses will return false on init failure.
  86 */
  87     virtual bool init();
  88
  89 /*! @function free
  90     @abstract The last reference is gone so clean up your resources.
  91     @discussion Release all resources held by the object, then call your parent's free().
  92
  93 <br><br>Caution:
  94 <br>1> You can not assume that you have completed initialization before your free is called, so be very careful in your implementation.
  95 <br>2> The implementation is OSObject::free() { delete this; } so do not call super::free() until just before you return.
  96 <br>3> Free is not allowed to fail all resource must be released on completion. */
  97     virtual void free();
  98
  99 /*! @function operator delete
 100     @abstract Release the 'operator new'ed memory.
 101     @discussion Never attempt to delete an object that inherits from OSObject directly use $link release().
 102     @param mem pointer to block of memory
 103     @param size size of block of memory
 104 */
 105     static void operator delete(void *mem, size_t size);
 106
 107 public:
 108
 109 /*! @function operator new
 110     @abstract Allocator for all objects that inherit from OSObject
 111     @param size number of bytes to allocate
 112     @result returns pointer to block of memory if available, 0 otherwise.
 113 */
 114     static void *operator new(size_t size);
 115
 116 /*! @function getRetainCount
 117     @abstract How many times has this object been retained?
 118     @result Current retain count
 119 */
 120     virtual int getRetainCount() const;
 121
 122 /*! @function retain
 123     @abstract Retain a reference in this object.
 124     @discussion Takes a reference that is NULL tagged.  See taggedRetain().
 125 */
 126     virtual void retain() const;
 127
 128 /*! @function release
 129     @abstract Release a reference to this object
 130     @discussion Removes a reference that is NULL tagged.  See taggedRelease().
 131 */
 132     virtual void release() const;
 133
 134 /*! @function taggedRetain
 135     @abstract Retain a tagged reference in this object.
 136     @param tag Retain a reference on this object with this tag, see taggedRelease.
 137 */
 138     virtual void taggedRetain(const void *tag = 0) const;
 139
 140 /*! @function taggedRelease
 141     @abstract Release a tagged reference to this object
 142     @param tag Remove a reference on this object with this tag, if an attempt is made to remove a reference that isn't associated with this tag the kernel will panic immediately.
 143 */
 144     virtual void taggedRelease(const void *tag = 0) const;
 145
 146 /*! @function serialize
 147     @abstract
 148     @discussion
 149     @param s
 150     @result
 151 */
 152     virtual bool serialize(OSSerialize *s) const;
 153
 154     // Unused Padding
 155     OSMetaClassDeclareReservedUnused(OSObject,  0);
 156     OSMetaClassDeclareReservedUnused(OSObject,  1);
 157     OSMetaClassDeclareReservedUnused(OSObject,  2);
 158     OSMetaClassDeclareReservedUnused(OSObject,  3);
 159     OSMetaClassDeclareReservedUnused(OSObject,  4);
 160     OSMetaClassDeclareReservedUnused(OSObject,  5);
 161     OSMetaClassDeclareReservedUnused(OSObject,  6);
 162     OSMetaClassDeclareReservedUnused(OSObject,  7);
 163     OSMetaClassDeclareReservedUnused(OSObject,  8);
 164     OSMetaClassDeclareReservedUnused(OSObject,  9);
 165     OSMetaClassDeclareReservedUnused(OSObject, 10);
 166     OSMetaClassDeclareReservedUnused(OSObject, 11);
 167     OSMetaClassDeclareReservedUnused(OSObject, 12);
 168     OSMetaClassDeclareReservedUnused(OSObject, 13);
 169     OSMetaClassDeclareReservedUnused(OSObject, 14);
 170     OSMetaClassDeclareReservedUnused(OSObject, 15);
 171     OSMetaClassDeclareReservedUnused(OSObject, 16);
 172     OSMetaClassDeclareReservedUnused(OSObject, 17);
 173     OSMetaClassDeclareReservedUnused(OSObject, 18);
 174     OSMetaClassDeclareReservedUnused(OSObject, 19);
 175     OSMetaClassDeclareReservedUnused(OSObject, 20);
 176     OSMetaClassDeclareReservedUnused(OSObject, 21);
 177     OSMetaClassDeclareReservedUnused(OSObject, 22);
 178     OSMetaClassDeclareReservedUnused(OSObject, 23);
 179     OSMetaClassDeclareReservedUnused(OSObject, 24);
 180     OSMetaClassDeclareReservedUnused(OSObject, 25);
 181     OSMetaClassDeclareReservedUnused(OSObject, 26);
 182     OSMetaClassDeclareReservedUnused(OSObject, 27);
 183     OSMetaClassDeclareReservedUnused(OSObject, 28);
 184     OSMetaClassDeclareReservedUnused(OSObject, 29);
 185     OSMetaClassDeclareReservedUnused(OSObject, 30);
 186     OSMetaClassDeclareReservedUnused(OSObject, 31);
 187 };
 188
 189 #endif /* !_LIBKERN_OSOBJECT_H */