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Introduce QObject
This commit introduces the qobject.h header file, it contains basic QObject definitions and helper macros. Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
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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 | ||
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#include <stddef.h> | ||
#include <assert.h> | ||
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typedef enum { | ||
QTYPE_NONE, | ||
} qtype_code; | ||
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struct QObject; | ||
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typedef struct QType { | ||
qtype_code code; | ||
void (*destroy)(struct QObject *); | ||
} QType; | ||
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typedef struct QObject { | ||
const QType *type; | ||
size_t refcnt; | ||
} QObject; | ||
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/* Objects definitions must include this */ | ||
#define QObject_HEAD \ | ||
QObject base | ||
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/* Get the 'base' part of an object */ | ||
#define QOBJECT(obj) (&obj->base) | ||
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/* High-level interface for qobject_incref() */ | ||
#define QINCREF(obj) \ | ||
assert(obj != NULL); \ | ||
qobject_incref(QOBJECT(obj)) | ||
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/* High-level interface for qobject_decref() */ | ||
#define QDECREF(obj) \ | ||
assert(obj != NULL); \ | ||
qobject_decref(QOBJECT(obj)) | ||
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/* Initialize an object to default values */ | ||
#define QOBJECT_INIT(obj, qtype_type) \ | ||
obj->base.refcnt = 1; \ | ||
obj->base.type = qtype_type | ||
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/** | ||
* qobject_incref(): Increment QObject's reference count | ||
*/ | ||
static inline void qobject_incref(QObject *obj) | ||
{ | ||
obj->refcnt++; | ||
} | ||
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/** | ||
* 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); | ||
} | ||
} | ||
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/** | ||
* qobject_type(): Return the QObject's type | ||
*/ | ||
static inline qtype_code qobject_type(const QObject *obj) | ||
{ | ||
assert(obj->type != NULL); | ||
return obj->type->code; | ||
} | ||
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#endif /* QOBJECT_H */ |