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 GPL, version 2.  See
  12  * the COPYING 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_code;
  43
  44 struct QObject;
  45
  46 typedef struct QType {
  47     qtype_code code;
  48     void (*destroy)(struct QObject *);
  49 } QType;
  50
  51 typedef struct QObject {
  52     const QType *type;
  53     size_t refcnt;
  54 } QObject;
  55
  56 /* Objects definitions must include this */
  57 #define QObject_HEAD  \
  58     QObject base
  59
  60 /* Get the 'base' part of an object */
  61 #define QOBJECT(obj) (&obj->base)
  62
  63 /* High-level interface for qobject_incref() */
  64 #define QINCREF(obj)      \
  65     assert(obj != NULL);  \
  66     qobject_incref(QOBJECT(obj))
  67
  68 /* High-level interface for qobject_decref() */
  69 #define QDECREF(obj)              \
  70     assert(obj != NULL);          \
  71     qobject_decref(QOBJECT(obj))
  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  */
  81 static inline void qobject_incref(QObject *obj)
  82 {
  83     obj->refcnt++;
  84 }
  85
  86 /**
  87  * qobject_decref(): Decrement QObject's reference count, deallocate
  88  * when it reaches zero
  89  */
  90 static inline void qobject_decref(QObject *obj)
  91 {
  92     if (--obj->refcnt == 0) {
  93         assert(obj->type != NULL);
  94         assert(obj->type->destroy != NULL);
  95         obj->type->destroy(obj);
  96     }
  97 }
  98
  99 /**
 100  * qobject_type(): Return the QObject's type
 101  */
 102 static inline qtype_code qobject_type(const QObject *obj)
 103 {
 104     assert(obj->type != NULL);
 105     return obj->type->code;
 106 }
 107
 108 #endif /* QOBJECT_H */