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, 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
  38typedef 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
  50struct QObject;
  51
  52typedef struct QType {
  53    qtype_code code;
  54    void (*destroy)(struct QObject *);
  55} QType;
  56
  57typedef 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 */
  81static 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 */
  91static inline void qobject_decref(QObject *obj)
  92{
  93    assert(!obj || obj->refcnt);
  94    if (obj && --obj->refcnt == 0) {
  95        assert(obj->type != NULL);
  96        assert(obj->type->destroy != NULL);
  97        obj->type->destroy(obj);
  98    }
  99}
 100
 101/**
 102 * qobject_type(): Return the QObject's type
 103 */
 104static inline qtype_code qobject_type(const QObject *obj)
 105{
 106    assert(obj->type != NULL);
 107    return obj->type->code;
 108}
 109
 110extern QObject qnull_;
 111
 112static inline QObject *qnull(void)
 113{
 114    qobject_incref(&qnull_);
 115    return &qnull_;
 116}
 117
 118#endif /* QOBJECT_H */
 119