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
  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_code;
  48
  49 struct QObject;
  50
  51 typedef struct QType {
  52     qtype_code code;
  53     void (*destroy)(struct QObject *);
  54 } QType;
  55
  56 typedef 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  */
  84 static 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  */
  94 static 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  */
 106 static 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 */