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 /*
49 * Preprocessor sorcery ahead: use a different identifier for the
50 * local variable in each expansion, so we can nest macro calls
51 * without shadowing variables.
52 */
53 #define QOBJECT_INTERNAL(obj, _obj) ({ \
54 typeof(obj) _obj = (obj); \
55 _obj ? container_of(&_obj->base, QObject, base) : NULL; \
56 })
57 #define QOBJECT(obj) QOBJECT_INTERNAL((obj), MAKE_IDENTIFIER(_obj))
58
59 /* Required for qobject_to() */
60 #define QTYPE_CAST_TO_QNull QTYPE_QNULL
61 #define QTYPE_CAST_TO_QNum QTYPE_QNUM
62 #define QTYPE_CAST_TO_QString QTYPE_QSTRING
63 #define QTYPE_CAST_TO_QDict QTYPE_QDICT
64 #define QTYPE_CAST_TO_QList QTYPE_QLIST
65 #define QTYPE_CAST_TO_QBool QTYPE_QBOOL
66
67 QEMU_BUILD_BUG_MSG(QTYPE__MAX != 7,
68 "The QTYPE_CAST_TO_* list needs to be extended");
69
70 #define qobject_to(type, obj) \
71 ((type *)qobject_check_type(obj, glue(QTYPE_CAST_TO_, type)))
72
qobject_ref_impl(QObject * obj)73 static inline void qobject_ref_impl(QObject *obj)
74 {
75 if (obj) {
76 obj->base.refcnt++;
77 }
78 }
79
80 /**
81 * qobject_is_equal(): Return whether the two objects are equal.
82 *
83 * Any of the pointers may be NULL; return true if both are. Always
84 * return false if only one is (therefore a QNull object is not
85 * considered equal to a NULL pointer).
86 */
87 bool qobject_is_equal(const QObject *x, const QObject *y);
88
89 /**
90 * qobject_destroy(): Free resources used by the object
91 * For use via qobject_unref() only!
92 */
93 void qobject_destroy(QObject *obj);
94
qobject_unref_impl(QObject * obj)95 static inline void qobject_unref_impl(QObject *obj)
96 {
97 assert(!obj || obj->base.refcnt);
98 if (obj && --obj->base.refcnt == 0) {
99 qobject_destroy(obj);
100 }
101 }
102
103 /**
104 * qobject_ref(): Increment QObject's reference count
105 *
106 * Returns: the same @obj. The type of @obj will be propagated to the
107 * return type.
108 */
109 #define qobject_ref(obj) ({ \
110 typeof(obj) _o = (obj); \
111 qobject_ref_impl(QOBJECT(_o)); \
112 _o; \
113 })
114
115 /**
116 * qobject_unref(): Decrement QObject's reference count, deallocate
117 * when it reaches zero
118 */
119 #define qobject_unref(obj) qobject_unref_impl(QOBJECT(obj))
120
121 /**
122 * qobject_type(): Return the QObject's type
123 */
qobject_type(const QObject * obj)124 static inline QType qobject_type(const QObject *obj)
125 {
126 assert(QTYPE_NONE < obj->base.type && obj->base.type < QTYPE__MAX);
127 return obj->base.type;
128 }
129
130 /**
131 * qobject_check_type(): Helper function for the qobject_to() macro.
132 * Return @obj, but only if @obj is not NULL and @type is equal to
133 * @obj's type. Return NULL otherwise.
134 */
qobject_check_type(const QObject * obj,QType type)135 static inline QObject *qobject_check_type(const QObject *obj, QType type)
136 {
137 if (obj && qobject_type(obj) == type) {
138 return (QObject *)obj;
139 } else {
140 return NULL;
141 }
142 }
143
144 #endif /* QOBJECT_H */
145