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      1 /*
      2  * QEMU Object Model.
      3  *
      4  * Based on ideas by Avi Kivity <avi (at) redhat.com>
      5  *
      6  * Copyright (C) 2009 Red Hat Inc.
      7  *
      8  * Authors:
      9  *  Luiz Capitulino <lcapitulino (at) 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_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 /* Objects definitions must include this */
     63 #define QObject_HEAD  \
     64     QObject base
     65 
     66 /* Get the 'base' part of an object */
     67 #define QOBJECT(obj) (&(obj)->base)
     68 
     69 /* High-level interface for qobject_incref() */
     70 #define QINCREF(obj)      \
     71     qobject_incref(QOBJECT(obj))
     72 
     73 /* High-level interface for qobject_decref() */
     74 #define QDECREF(obj)              \
     75     qobject_decref(obj ? QOBJECT(obj) : NULL)
     76 
     77 /* Initialize an object to default values */
     78 #define QOBJECT_INIT(obj, qtype_type)   \
     79     obj->base.refcnt = 1;               \
     80     obj->base.type   = qtype_type
     81 
     82 /**
     83  * qobject_incref(): Increment QObject's reference count
     84  */
     85 static inline void qobject_incref(QObject *obj)
     86 {
     87     if (obj)
     88         obj->refcnt++;
     89 }
     90 
     91 /**
     92  * qobject_decref(): Decrement QObject's reference count, deallocate
     93  * when it reaches zero
     94  */
     95 static inline void qobject_decref(QObject *obj)
     96 {
     97     if (obj && --obj->refcnt == 0) {
     98         assert(obj->type != NULL);
     99         assert(obj->type->destroy != NULL);
    100         obj->type->destroy(obj);
    101     }
    102 }
    103 
    104 /**
    105  * qobject_type(): Return the QObject's type
    106  */
    107 static inline qtype_code qobject_type(const QObject *obj)
    108 {
    109     assert(obj->type != NULL);
    110     return obj->type->code;
    111 }
    112 
    113 #endif /* QOBJECT_H */
    114