include/qapi/qmp/qobject.h

   1 /*
   2  * QEMU Object Model.
   3  *
   4  * Based on ideas by Avi Kivity <avi@redhat.com>
   5  *
   6  * Copyright (C) 2009, 2015 Red Hat Inc.
   7  *
   8  * Authors:
   9  *  Luiz Capitulino <lcapitulino@redhat.com>
  10  *
  11  * This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
  12  * See the COPYING.LIB file in the top-level directory.
  13  *
  14  * QObject Reference Counts Terminology
  15  * ------------------------------------
  16  *
  17  *  - Returning references: A function that returns an object may
  18  *  return it as either a weak or a strong reference.  If the
  19  *  reference is strong, you are responsible for calling
  20  *  qobject_unref() on the reference when you are done.
  21  *
  22  *  If the reference is weak, the owner of the reference may free it at
  23  *  any time in the future.  Before storing the reference anywhere, you
  24  *  should call qobject_ref() to make the reference strong.
  25  *
  26  *  - Transferring ownership: when you transfer ownership of a reference
  27  *  by calling a function, you are no longer responsible for calling
  28  *  qobject_unref() when the reference is no longer needed.  In other words,
  29  *  when the function returns you must behave as if the reference to the
  30  *  passed object was weak.
  31  */
  32 #ifndef QOBJECT_H
  33 #define QOBJECT_H
  34
  35 #include "qapi/qapi-builtin-types.h"
  36
  37 /* Not for use outside include/qapi/qmp/ */
  38 struct QObjectBase_ {
  39     QType type;
  40     size_t refcnt;
  41 };
  42
  43 /* this struct must have no other members than base */
  44 struct QObject {
  45     struct QObjectBase_ base;
  46 };
  47
  48 #define QOBJECT(obj) ({                                         \
  49     typeof(obj) _obj = (obj);                                   \
  50     _obj ? container_of(&(_obj)->base, QObject, base) : NULL;   \
  51 })
  52
  53 /* Required for qobject_to() */
  54 #define QTYPE_CAST_TO_QNull     QTYPE_QNULL
  55 #define QTYPE_CAST_TO_QNum      QTYPE_QNUM
  56 #define QTYPE_CAST_TO_QString   QTYPE_QSTRING
  57 #define QTYPE_CAST_TO_QDict     QTYPE_QDICT
  58 #define QTYPE_CAST_TO_QList     QTYPE_QLIST
  59 #define QTYPE_CAST_TO_QBool     QTYPE_QBOOL
  60
  61 QEMU_BUILD_BUG_MSG(QTYPE__MAX != 7,
  62                    "The QTYPE_CAST_TO_* list needs to be extended");
  63
  64 #define qobject_to(type, obj)                                       \
  65     ((type *)qobject_check_type(obj, glue(QTYPE_CAST_TO_, type)))
  66
  67 /* Initialize an object to default values */
  68 static inline void qobject_init(QObject *obj, QType type)
  69 {
  70     assert(QTYPE_NONE < type && type < QTYPE__MAX);
  71     obj->base.refcnt = 1;
  72     obj->base.type = type;
  73 }
  74
  75 static inline void qobject_ref_impl(QObject *obj)
  76 {
  77     if (obj) {
  78         obj->base.refcnt++;
  79     }
  80 }
  81
  82 /**
  83  * qobject_is_equal(): Return whether the two objects are equal.
  84  *
  85  * Any of the pointers may be NULL; return true if both are.  Always
  86  * return false if only one is (therefore a QNull object is not
  87  * considered equal to a NULL pointer).
  88  */
  89 bool qobject_is_equal(const QObject *x, const QObject *y);
  90
  91 /**
  92  * qobject_destroy(): Free resources used by the object
  93  */
  94 void qobject_destroy(QObject *obj);
  95
  96 static inline void qobject_unref_impl(QObject *obj)
  97 {
  98     assert(!obj || obj->base.refcnt);
  99     if (obj && --obj->base.refcnt == 0) {
 100         qobject_destroy(obj);
 101     }
 102 }
 103
 104 /**
 105  * qobject_ref(): Increment QObject's reference count
 106  *
 107  * Returns: the same @obj. The type of @obj will be propagated to the
 108  * return type.
 109  */
 110 #define qobject_ref(obj) ({                     \
 111     typeof(obj) _o = (obj);                     \
 112     qobject_ref_impl(QOBJECT(_o));              \
 113     _o;                                         \
 114 })
 115
 116 /**
 117  * qobject_unref(): Decrement QObject's reference count, deallocate
 118  * when it reaches zero
 119  */
 120 #define qobject_unref(obj) qobject_unref_impl(QOBJECT(obj))
 121
 122 /**
 123  * qobject_type(): Return the QObject's type
 124  */
 125 static inline QType qobject_type(const QObject *obj)
 126 {
 127     assert(QTYPE_NONE < obj->base.type && obj->base.type < QTYPE__MAX);
 128     return obj->base.type;
 129 }
 130
 131 /**
 132  * qobject_check_type(): Helper function for the qobject_to() macro.
 133  * Return @obj, but only if @obj is not NULL and @type is equal to
 134  * @obj's type.  Return NULL otherwise.
 135  */
 136 static inline QObject *qobject_check_type(const QObject *obj, QType type)
 137 {
 138     if (obj && qobject_type(obj) == type) {
 139         return (QObject *)obj;
 140     } else {
 141         return NULL;
 142     }
 143 }
 144
 145 #endif /* QOBJECT_H */