xref: /openbmc/qemu/include/qapi/qmp/qobject.h (revision 80adf54e)
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 reference
19  *  is strong, you are responsible for calling QDECREF() on the reference
20  *  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 QINCREF() 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  *  QDECREF() 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-types.h"
36 
37 struct QObject {
38     QType type;
39     size_t refcnt;
40 };
41 
42 /* Get the 'base' part of an object */
43 #define QOBJECT(obj) (&(obj)->base)
44 
45 /* High-level interface for qobject_incref() */
46 #define QINCREF(obj)      \
47     qobject_incref(QOBJECT(obj))
48 
49 /* High-level interface for qobject_decref() */
50 #define QDECREF(obj)              \
51     qobject_decref(obj ? QOBJECT(obj) : NULL)
52 
53 /* Initialize an object to default values */
54 static inline void qobject_init(QObject *obj, QType type)
55 {
56     assert(QTYPE_NONE < type && type < QTYPE__MAX);
57     obj->refcnt = 1;
58     obj->type = type;
59 }
60 
61 /**
62  * qobject_incref(): Increment QObject's reference count
63  */
64 static inline void qobject_incref(QObject *obj)
65 {
66     if (obj)
67         obj->refcnt++;
68 }
69 
70 /**
71  * qobject_destroy(): Free resources used by the object
72  */
73 void qobject_destroy(QObject *obj);
74 
75 /**
76  * qobject_decref(): Decrement QObject's reference count, deallocate
77  * when it reaches zero
78  */
79 static inline void qobject_decref(QObject *obj)
80 {
81     assert(!obj || obj->refcnt);
82     if (obj && --obj->refcnt == 0) {
83         qobject_destroy(obj);
84     }
85 }
86 
87 /**
88  * qobject_type(): Return the QObject's type
89  */
90 static inline QType qobject_type(const QObject *obj)
91 {
92     assert(QTYPE_NONE < obj->type && obj->type < QTYPE__MAX);
93     return obj->type;
94 }
95 
96 struct QNull {
97     QObject base;
98 };
99 
100 extern QNull qnull_;
101 
102 static inline QNull *qnull(void)
103 {
104     QINCREF(&qnull_);
105     return &qnull_;
106 }
107 
108 #endif /* QOBJECT_H */
109