libkern/libkern/c++/OSObject.h

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_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. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23 /*
  24 Copyright (c) 1998 Apple Computer, Inc.  All rights reserved.
  25 HISTORY
  26     1998-10-30  Godfrey van der Linden(gvdl)
  27         Created
  28 */
  29 #ifndef _LIBKERN_OSOBJECT_H
  30 #define _LIBKERN_OSOBJECT_H
  31
  32 #include <libkern/c++/OSMetaClass.h>
  33
  34 class OSSymbol;
  35 class OSString;
  36 /*!
  37     @class OSObject : OSMetaClassBase
  38     @abstract The root base class for Mac OS X kernel and just generally all-round useful class to have around.
  39     @discussion
  40 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.
  41
  42 <br><br> Construction <br><br>
  43
  44 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.
  45
  46 <br><br>Reference Counting<br><br>
  47
  48 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.
  49 <br>
  50 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);
  51
  52 <br><br>Runtime Type Information System<br><br>
  53
  54 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.
  55 */
  56 class OSObject : public OSMetaClassBase
  57 {
  58     OSDeclareAbstractStructors(OSObject)
  59
  60 private:
  61 /*! @var retainCount Number of references held on this instance. */
  62     mutable int retainCount;
  63
  64 protected:
  65
  66 /*! @function release
  67     @abstract untagged release(when) mechansim.
  68     @param when Pass through to taggedRelease. */
  69     virtual void release(int when) const;
  70
  71 /*! @function taggedRelease
  72     @abstract Primary implementation of the tagged release mechanism.
  73     @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.
  74     @param when If retainCount == when then call free(). */
  75     virtual void taggedRelease(const void *tag, const int when) const;
  76
  77 /*! @function init
  78     @abstract Mac OS X kernel's primary mechanism for constructing objects.
  79     @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.
  80     @result OSObject::init Always returns true, but subclasses will return false on init failure.
  81 */
  82     virtual bool init();
  83
  84 /*! @function free
  85     @abstract The last reference is gone so clean up your resources.
  86     @discussion Release all resources held by the object, then call your parent's free().
  87
  88 <br><br>Caution:
  89 <br>1> You can not assume that you have completed initialization before your free is called, so be very careful in your implementation.
  90 <br>2> The implementation is OSObject::free() { delete this; } so do not call super::free() until just before you return.
  91 <br>3> Free is not allowed to fail all resource must be released on completion. */
  92     virtual void free();
  93
  94 /*! @function operator delete
  95     @abstract Release the 'operator new'ed memory.
  96     @discussion Never attempt to delete an object that inherits from OSObject directly use $link release().
  97     @param mem pointer to block of memory
  98     @param size size of block of memory
  99 */
 100     static void operator delete(void *mem, size_t size);
 101
 102 public:
 103
 104 /*! @function operator new
 105     @abstract Allocator for all objects that inherit from OSObject
 106     @param size number of bytes to allocate
 107     @result returns pointer to block of memory if available, 0 otherwise.
 108 */
 109     static void *operator new(size_t size);
 110
 111 /*! @function getRetainCount
 112     @abstract How many times has this object been retained?
 113     @result Current retain count
 114 */
 115     virtual int getRetainCount() const;
 116
 117 /*! @function retain
 118     @abstract Retain a reference in this object.
 119     @discussion Takes a reference that is NULL tagged.  See taggedRetain().
 120 */
 121     virtual void retain() const;
 122
 123 /*! @function release
 124     @abstract Release a reference to this object
 125     @discussion Removes a reference that is NULL tagged.  See taggedRelease().
 126 */
 127     virtual void release() const;
 128
 129 /*! @function taggedRetain
 130     @abstract Retain a tagged reference in this object.
 131     @param tag Retain a reference on this object with this tag, see taggedRelease.
 132 */
 133     virtual void taggedRetain(const void *tag = 0) const;
 134
 135 /*! @function taggedRelease
 136     @abstract Release a tagged reference to this object
 137     @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.
 138 */
 139     virtual void taggedRelease(const void *tag = 0) const;
 140
 141 /*! @function serialize
 142     @abstract
 143     @discussion
 144     @param s
 145     @result
 146 */
 147     virtual bool serialize(OSSerialize *s) const;
 148
 149     // Unused Padding
 150     OSMetaClassDeclareReservedUnused(OSObject,  0);
 151     OSMetaClassDeclareReservedUnused(OSObject,  1);
 152     OSMetaClassDeclareReservedUnused(OSObject,  2);
 153     OSMetaClassDeclareReservedUnused(OSObject,  3);
 154     OSMetaClassDeclareReservedUnused(OSObject,  4);
 155     OSMetaClassDeclareReservedUnused(OSObject,  5);
 156     OSMetaClassDeclareReservedUnused(OSObject,  6);
 157     OSMetaClassDeclareReservedUnused(OSObject,  7);
 158     OSMetaClassDeclareReservedUnused(OSObject,  8);
 159     OSMetaClassDeclareReservedUnused(OSObject,  9);
 160     OSMetaClassDeclareReservedUnused(OSObject, 10);
 161     OSMetaClassDeclareReservedUnused(OSObject, 11);
 162     OSMetaClassDeclareReservedUnused(OSObject, 12);
 163     OSMetaClassDeclareReservedUnused(OSObject, 13);
 164     OSMetaClassDeclareReservedUnused(OSObject, 14);
 165     OSMetaClassDeclareReservedUnused(OSObject, 15);
 166     OSMetaClassDeclareReservedUnused(OSObject, 16);
 167     OSMetaClassDeclareReservedUnused(OSObject, 17);
 168     OSMetaClassDeclareReservedUnused(OSObject, 18);
 169     OSMetaClassDeclareReservedUnused(OSObject, 19);
 170     OSMetaClassDeclareReservedUnused(OSObject, 20);
 171     OSMetaClassDeclareReservedUnused(OSObject, 21);
 172     OSMetaClassDeclareReservedUnused(OSObject, 22);
 173     OSMetaClassDeclareReservedUnused(OSObject, 23);
 174     OSMetaClassDeclareReservedUnused(OSObject, 24);
 175     OSMetaClassDeclareReservedUnused(OSObject, 25);
 176     OSMetaClassDeclareReservedUnused(OSObject, 26);
 177     OSMetaClassDeclareReservedUnused(OSObject, 27);
 178     OSMetaClassDeclareReservedUnused(OSObject, 28);
 179     OSMetaClassDeclareReservedUnused(OSObject, 29);
 180     OSMetaClassDeclareReservedUnused(OSObject, 30);
 181     OSMetaClassDeclareReservedUnused(OSObject, 31);
 182 };
 183
 184 #endif /* !_LIBKERN_OSOBJECT_H */