libkern/libkern/c++/OSObject.h

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * The contents of this file constitute Original Code as defined in and
   7  * are subject to the Apple Public Source License Version 1.1 (the
   8  * "License").  You may not use this file except in compliance with the
   9  * License.  Please obtain a copy of the License at
  10  * http://www.apple.com/publicsource and read it before using this file.
  11  *
  12  * This Original Code and all software distributed under the License are
  13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  17  * License for the specific language governing rights and limitations
  18  * under the License.
  19  *
  20  * @APPLE_LICENSE_HEADER_END@
  21  */
  22 /*
  23 Copyright (c) 1998 Apple Computer, Inc.  All rights reserved.
  24 HISTORY
  25     1998-10-30  Godfrey van der Linden(gvdl)
  26         Created
  27 */
  28 #ifndef _LIBKERN_OSOBJECT_H
  29 #define _LIBKERN_OSOBJECT_H
  30
  31 #include <libkern/c++/OSMetaClass.h>
  32
  33 class OSSymbol;
  34 class OSString;
  35 /*!
  36     @class OSObject : OSMetaClassBase
  37     @abstract The root base class for Mac OS X kernel and just generally all-round useful class to have around.
  38     @discussion
  39 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.
  40
  41 <br><br> Construction <br><br>
  42
  43 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.
  44
  45 <br><br>Reference Counting<br><br>
  46
  47 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.
  48 <br>
  49 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);
  50
  51 <br><br>Runtime Type Information System<br><br>
  52
  53 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.
  54 */
  55 class OSObject : public OSMetaClassBase
  56 {
  57     OSDeclareAbstractStructors(OSObject)
  58
  59 private:
  60 /*! @var retainCount Number of references held on this instance. */
  61     mutable int retainCount;
  62
  63 protected:
  64
  65 /*! @function release
  66     @abstract untagged release(when) mechansim.
  67     @param when Pass through to taggedRelease. */
  68     virtual void release(int when) const;
  69
  70 /*! @function taggedRelease
  71     @abstract Primary implementation of the tagged release mechanism.
  72     @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.
  73     @param when If retainCount == when then call free(). */
  74     virtual void taggedRelease(const void *tag, const int when) const;
  75
  76 /*! @function init
  77     @abstract Mac OS X kernel's primary mechanism for constructing objects.
  78     @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.
  79     @result OSObject::init Always returns true, but subclasses will return false on init failure.
  80 */
  81     virtual bool init();
  82
  83 /*! @function free
  84     @abstract The last reference is gone so clean up your resources.
  85     @discussion Release all resources held by the object, then call your parent's free().
  86
  87 <br><br>Caution:
  88 <br>1> You can not assume that you have completed initialization before your free is called, so be very careful in your implementation.
  89 <br>2> The implementation is OSObject::free() { delete this; } so do not call super::free() until just before you return.
  90 <br>3> Free is not allowed to fail all resource must be released on completion. */
  91     virtual void free();
  92
  93 /*! @function operator delete
  94     @abstract Release the 'operator new'ed memory.
  95     @discussion Never attempt to delete an object that inherits from OSObject directly use $link release().
  96     @param mem pointer to block of memory
  97     @param size size of block of memory
  98 */
  99     static void operator delete(void *mem, size_t size);
 100
 101 public:
 102
 103 /*! @function operator new
 104     @abstract Allocator for all objects that inherit from OSObject
 105     @param size number of bytes to allocate
 106     @result returns pointer to block of memory if available, 0 otherwise.
 107 */
 108     static void *operator new(size_t size);
 109
 110 /*! @function getRetainCount
 111     @abstract How many times has this object been retained?
 112     @result Current retain count
 113 */
 114     virtual int getRetainCount() const;
 115
 116 /*! @function retain
 117     @abstract Retain a reference in this object.
 118     @discussion Takes a reference that is NULL tagged.  See taggedRetain().
 119 */
 120     virtual void retain() const;
 121
 122 /*! @function release
 123     @abstract Release a reference to this object
 124     @discussion Removes a reference that is NULL tagged.  See taggedRelease().
 125 */
 126     virtual void release() const;
 127
 128 /*! @function taggedRetain
 129     @abstract Retain a tagged reference in this object.
 130     @param tag Retain a reference on this object with this tag, see taggedRelease.
 131 */
 132     virtual void taggedRetain(const void *tag = 0) const;
 133
 134 /*! @function taggedRelease
 135     @abstract Release a tagged reference to this object
 136     @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.
 137 */
 138     virtual void taggedRelease(const void *tag = 0) const;
 139
 140 /*! @function serialize
 141     @abstract
 142     @discussion
 143     @param s
 144     @result
 145 */
 146     virtual bool serialize(OSSerialize *s) const;
 147
 148     // Unused Padding
 149     OSMetaClassDeclareReservedUnused(OSObject,  0);
 150     OSMetaClassDeclareReservedUnused(OSObject,  1);
 151     OSMetaClassDeclareReservedUnused(OSObject,  2);
 152     OSMetaClassDeclareReservedUnused(OSObject,  3);
 153     OSMetaClassDeclareReservedUnused(OSObject,  4);
 154     OSMetaClassDeclareReservedUnused(OSObject,  5);
 155     OSMetaClassDeclareReservedUnused(OSObject,  6);
 156     OSMetaClassDeclareReservedUnused(OSObject,  7);
 157     OSMetaClassDeclareReservedUnused(OSObject,  8);
 158     OSMetaClassDeclareReservedUnused(OSObject,  9);
 159     OSMetaClassDeclareReservedUnused(OSObject, 10);
 160     OSMetaClassDeclareReservedUnused(OSObject, 11);
 161     OSMetaClassDeclareReservedUnused(OSObject, 12);
 162     OSMetaClassDeclareReservedUnused(OSObject, 13);
 163     OSMetaClassDeclareReservedUnused(OSObject, 14);
 164     OSMetaClassDeclareReservedUnused(OSObject, 15);
 165     OSMetaClassDeclareReservedUnused(OSObject, 16);
 166     OSMetaClassDeclareReservedUnused(OSObject, 17);
 167     OSMetaClassDeclareReservedUnused(OSObject, 18);
 168     OSMetaClassDeclareReservedUnused(OSObject, 19);
 169     OSMetaClassDeclareReservedUnused(OSObject, 20);
 170     OSMetaClassDeclareReservedUnused(OSObject, 21);
 171     OSMetaClassDeclareReservedUnused(OSObject, 22);
 172     OSMetaClassDeclareReservedUnused(OSObject, 23);
 173     OSMetaClassDeclareReservedUnused(OSObject, 24);
 174     OSMetaClassDeclareReservedUnused(OSObject, 25);
 175     OSMetaClassDeclareReservedUnused(OSObject, 26);
 176     OSMetaClassDeclareReservedUnused(OSObject, 27);
 177     OSMetaClassDeclareReservedUnused(OSObject, 28);
 178     OSMetaClassDeclareReservedUnused(OSObject, 29);
 179     OSMetaClassDeclareReservedUnused(OSObject, 30);
 180     OSMetaClassDeclareReservedUnused(OSObject, 31);
 181 };
 182
 183 #endif /* !_LIBKERN_OSOBJECT_H */