xref: /illumos-kvm-cmd/qobject.h (revision 68396ea9)
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 
38 typedef 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 
49 struct QObject;
50 
51 typedef struct QType {
52     qtype_code code;
53     void (*destroy)(struct QObject *);
54 } QType;
55 
56 typedef 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  */
qobject_incref(QObject * obj)84 static 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  */
qobject_decref(QObject * obj)94 static 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  */
qobject_type(const QObject * obj)106 static 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