include/qapi/qmp/qobject.h

   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 */