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 <stddef.h> 36 #include <assert.h> 37 38 typedef enum { 39 QTYPE_NONE, /* sentinel value, no QObject has this type code */ 40 QTYPE_QNULL, 41 QTYPE_QINT, 42 QTYPE_QSTRING, 43 QTYPE_QDICT, 44 QTYPE_QLIST, 45 QTYPE_QFLOAT, 46 QTYPE_QBOOL, 47 QTYPE_MAX, 48 } qtype_code; 49 50 struct QObject; 51 52 typedef struct QType { 53 qtype_code code; 54 void (*destroy)(struct QObject *); 55 } QType; 56 57 typedef struct QObject { 58 const QType *type; 59 size_t refcnt; 60 } QObject; 61 62 /* Get the 'base' part of an object */ 63 #define QOBJECT(obj) (&(obj)->base) 64 65 /* High-level interface for qobject_incref() */ 66 #define QINCREF(obj) \ 67 qobject_incref(QOBJECT(obj)) 68 69 /* High-level interface for qobject_decref() */ 70 #define QDECREF(obj) \ 71 qobject_decref(obj ? QOBJECT(obj) : NULL) 72 73 /* Initialize an object to default values */ 74 #define QOBJECT_INIT(obj, qtype_type) \ 75 obj->base.refcnt = 1; \ 76 obj->base.type = qtype_type 77 78 /** 79 * qobject_incref(): Increment QObject's reference count 80 */ 81 static inline void qobject_incref(QObject *obj) 82 { 83 if (obj) 84 obj->refcnt++; 85 } 86 87 /** 88 * qobject_decref(): Decrement QObject's reference count, deallocate 89 * when it reaches zero 90 */ 91 static inline void qobject_decref(QObject *obj) 92 { 93 if (obj && --obj->refcnt == 0) { 94 assert(obj->type != NULL); 95 assert(obj->type->destroy != NULL); 96 obj->type->destroy(obj); 97 } 98 } 99 100 /** 101 * qobject_type(): Return the QObject's type 102 */ 103 static inline qtype_code qobject_type(const QObject *obj) 104 { 105 assert(obj->type != NULL); 106 return obj->type->code; 107 } 108 109 extern QObject qnull_; 110 111 static inline QObject *qnull(void) 112 { 113 qobject_incref(&qnull_); 114 return &qnull_; 115 } 116 117 #endif /* QOBJECT_H */ 118