55e1819c50
The QObject hierarchy is small enough, and unlikely to grow further (since we only use it to map to JSON and already cover all JSON types), that we can simplify things by not tracking a separate vtable, but just inline the code element of the vtable QType directly into QObject (renamed to type), and track a separate array of destroy functions. We can drop qnull_destroy_obj() in the process. The remaining QObject subclasses must export their destructor. This also has the nice benefit of moving the typename 'QType' out of the way, so that the next patch can repurpose it for a nicer name for 'qtype_code'. The various objects are still the same size (so no change in cache line pressure), but now have less indirection (although I didn't bother benchmarking to see if there is a noticeable speedup, as we don't have hard evidence that this was in a performance hotspot in the first place). A future patch could drop the refcnt size to 32 bits for a smaller struct on 64-bit architectures, if desired (we have limits on the largest JSON that we are willing to parse, and will probably never need to take full advantage of a 64-bit refcnt). Suggested-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <1449033659-25497-2-git-send-email-eblake@redhat.com> Signed-off-by: Markus Armbruster <armbru@redhat.com>
118 lines
2.9 KiB
C
118 lines
2.9 KiB
C
/*
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* QEMU Object Model.
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*
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* Based on ideas by Avi Kivity <avi@redhat.com>
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*
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* Copyright (C) 2009, 2015 Red Hat Inc.
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*
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* Authors:
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* Luiz Capitulino <lcapitulino@redhat.com>
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*
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* This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
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* See the COPYING.LIB file in the top-level directory.
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*
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* QObject Reference Counts Terminology
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* ------------------------------------
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*
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* - Returning references: A function that returns an object may
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* return it as either a weak or a strong reference. If the reference
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* is strong, you are responsible for calling QDECREF() on the reference
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* when you are done.
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*
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* If the reference is weak, the owner of the reference may free it at
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* any time in the future. Before storing the reference anywhere, you
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* should call QINCREF() to make the reference strong.
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*
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* - Transferring ownership: when you transfer ownership of a reference
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* by calling a function, you are no longer responsible for calling
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* QDECREF() when the reference is no longer needed. In other words,
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* when the function returns you must behave as if the reference to the
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* passed object was weak.
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*/
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#ifndef QOBJECT_H
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#define QOBJECT_H
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#include <stddef.h>
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#include <assert.h>
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typedef enum {
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QTYPE_NONE, /* sentinel value, no QObject has this type code */
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QTYPE_QNULL,
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QTYPE_QINT,
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QTYPE_QSTRING,
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QTYPE_QDICT,
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QTYPE_QLIST,
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QTYPE_QFLOAT,
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QTYPE_QBOOL,
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QTYPE_MAX,
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} qtype_code;
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typedef struct QObject {
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qtype_code type;
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size_t refcnt;
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} QObject;
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/* Get the 'base' part of an object */
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#define QOBJECT(obj) (&(obj)->base)
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/* High-level interface for qobject_incref() */
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#define QINCREF(obj) \
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qobject_incref(QOBJECT(obj))
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/* High-level interface for qobject_decref() */
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#define QDECREF(obj) \
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qobject_decref(obj ? QOBJECT(obj) : NULL)
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/* Initialize an object to default values */
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static inline void qobject_init(QObject *obj, qtype_code type)
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{
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assert(QTYPE_NONE < type && type < QTYPE_MAX);
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obj->refcnt = 1;
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obj->type = type;
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}
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/**
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* qobject_incref(): Increment QObject's reference count
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*/
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static inline void qobject_incref(QObject *obj)
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{
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if (obj)
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obj->refcnt++;
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}
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/**
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* qobject_destroy(): Free resources used by the object
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*/
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void qobject_destroy(QObject *obj);
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/**
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* qobject_decref(): Decrement QObject's reference count, deallocate
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* when it reaches zero
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*/
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static inline void qobject_decref(QObject *obj)
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{
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assert(!obj || obj->refcnt);
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if (obj && --obj->refcnt == 0) {
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qobject_destroy(obj);
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}
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}
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/**
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* qobject_type(): Return the QObject's type
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*/
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static inline qtype_code qobject_type(const QObject *obj)
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{
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assert(QTYPE_NONE < obj->type && obj->type < QTYPE_MAX);
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return obj->type;
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}
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extern QObject qnull_;
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static inline QObject *qnull(void)
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{
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qobject_incref(&qnull_);
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return &qnull_;
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}
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#endif /* QOBJECT_H */
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