Home | History | Annotate | Download | only in qemu 
      1 /*
      2  * QEMU Object Model.
      3  *
      4  * Based on ideas by Avi Kivity <avi (at) redhat.com>
      5  *
      6  * Copyright (C) 2009 Red Hat Inc.
      7  *
      8  * Authors:
      9  *  Luiz Capitulino <lcapitulino (at) 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(QOBJECT(obj))
     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 */
    113