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