1/*
2 * QEMU Object Model.
3 *
4 * Based on ideas by Avi Kivity <avi@redhat.com>
5 *
6 * Copyright (C) 2009 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 <stddef.h>
36#include <assert.h>
37
38typedef enum {
39    QTYPE_NONE,
40    QTYPE_QINT,
41    QTYPE_QSTRING,
42    QTYPE_QDICT,
43    QTYPE_QLIST,
44    QTYPE_QFLOAT,
45    QTYPE_QBOOL,
46    QTYPE_QERROR,
47} qtype_code;
48
49struct QObject;
50
51typedef struct QType {
52    qtype_code code;
53    void (*destroy)(struct QObject *);
54} QType;
55
56typedef struct QObject {
57    const QType *type;
58    size_t refcnt;
59} QObject;
60
61/* Objects definitions must include this */
62#define QObject_HEAD  \
63    QObject base
64
65/* Get the 'base' part of an object */
66#define QOBJECT(obj) (&(obj)->base)
67
68/* High-level interface for qobject_incref() */
69#define QINCREF(obj)      \
70    qobject_incref(QOBJECT(obj))
71
72/* High-level interface for qobject_decref() */
73#define QDECREF(obj)              \
74    qobject_decref(QOBJECT(obj))
75
76/* Initialize an object to default values */
77#define QOBJECT_INIT(obj, qtype_type)   \
78    obj->base.refcnt = 1;               \
79    obj->base.type   = qtype_type
80
81/**
82 * qobject_incref(): Increment QObject's reference count
83 */
84static inline void qobject_incref(QObject *obj)
85{
86    if (obj)
87        obj->refcnt++;
88}
89
90/**
91 * qobject_decref(): Decrement QObject's reference count, deallocate
92 * when it reaches zero
93 */
94static inline void qobject_decref(QObject *obj)
95{
96    if (obj && --obj->refcnt == 0) {
97        assert(obj->type != NULL);
98        assert(obj->type->destroy != NULL);
99        obj->type->destroy(obj);
100    }
101}
102
103/**
104 * qobject_type(): Return the QObject's type
105 */
106static inline qtype_code qobject_type(const QObject *obj)
107{
108    assert(obj->type != NULL);
109    return obj->type->code;
110}
111
112#endif /* QOBJECT_H */
113