LXR qemu/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 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
  38typedef 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
  49struct QObject;
  50
  51typedef struct QType {
  52    qtype_code code;
  53    void (*destroy)(struct QObject *);
  54} QType;
  55
  56typedef 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(obj ? QOBJECT(obj) : NULL)
  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 */
  84static 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 */
  94static 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 */
 106static 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