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/*

 * QEMU Object Model.

 *

 * Based on ideas by Avi Kivity <avi@redhat.com>

 *

 * Copyright (C) 2009 Red Hat Inc.

 *

 * Authors:

 *  Luiz Capitulino <lcapitulino@redhat.com>

 *

 * This work is licensed under the terms of the GNU GPL, version 2.  See

 * the COPYING file in the top-level directory.

 *

 * QObject Reference Counts Terminology

 * ------------------------------------

 *

 *  - Returning references: A function that returns an object may

 *  return it as either a weak or a strong reference.  If the reference

 *  is strong, you are responsible for calling QDECREF() on the reference

 *  when you are done.

 *

 *  If the reference is weak, the owner of the reference may free it at

 *  any time in the future.  Before storing the reference anywhere, you

 *  should call QINCREF() to make the reference strong.

 *

 *  - Transferring ownership: when you transfer ownership of a reference

 *  by calling a function, you are no longer responsible for calling

 *  QDECREF() when the reference is no longer needed.  In other words,

 *  when the function returns you must behave as if the reference to the

 *  passed object was weak.

 */

#ifndef QOBJECT_H

#define QOBJECT_H

#include <stddef.h>

#include <assert.h>

typedef enum {

    QTYPE_NONE,

    QTYPE_QINT,

    QTYPE_QSTRING,

} qtype_code;

struct QObject;

typedef struct QType {

    qtype_code code;

    void (*destroy)(struct QObject *);

} QType;

typedef struct QObject {

    const QType *type;

    size_t refcnt;

} QObject;

/* Objects definitions must include this */

#define QObject_HEAD  \

    QObject base

/* Get the 'base' part of an object */

#define QOBJECT(obj) (&obj->base)

/* High-level interface for qobject_incref() */

#define QINCREF(obj)      \

    assert(obj != NULL);  \

    qobject_incref(QOBJECT(obj))

/* High-level interface for qobject_decref() */

#define QDECREF(obj)              \

    assert(obj != NULL);          \

    qobject_decref(QOBJECT(obj))

/* Initialize an object to default values */

#define QOBJECT_INIT(obj, qtype_type)   \

    obj->base.refcnt = 1;               \

    obj->base.type   = qtype_type

/**

 * qobject_incref(): Increment QObject's reference count

 */

static inline void qobject_incref(QObject *obj)

{

    obj->refcnt++;

}

/**

 * qobject_decref(): Decrement QObject's reference count, deallocate

 * when it reaches zero

 */

static inline void qobject_decref(QObject *obj)

{

    if (--obj->refcnt == 0) {

        assert(obj->type != NULL);

        assert(obj->type->destroy != NULL);

        obj->type->destroy(obj);

    }

}

/**

 * qobject_type(): Return the QObject's type

 */

static inline qtype_code qobject_type(const QObject *obj)

{

    assert(obj->type != NULL);

    return obj->type->code;

}

#endif /* QOBJECT_H */