qobject: Simplify QObject

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>

include/qapi/qmp/qbool.h

@@ -25,5 +25,6 @@ typedef struct QBool {
 QBool *qbool_from_bool(bool value);
 bool qbool_get_bool(const QBool *qb);
 QBool *qobject_to_qbool(const QObject *obj);
+void qbool_destroy_obj(QObject *obj);
 
 #endif /* QBOOL_H */

include/qapi/qmp/qdict.h

@@ -48,6 +48,7 @@ void qdict_iter(const QDict *qdict,
                 void *opaque);
 const QDictEntry *qdict_first(const QDict *qdict);
 const QDictEntry *qdict_next(const QDict *qdict, const QDictEntry *entry);
+void qdict_destroy_obj(QObject *obj);
 
 /* Helper to qdict_put_obj(), accepts any object */
 #define qdict_put(qdict, key, obj) \

include/qapi/qmp/qfloat.h

@@ -25,5 +25,6 @@ typedef struct QFloat {
 QFloat *qfloat_from_double(double value);
 double qfloat_get_double(const QFloat *qi);
 QFloat *qobject_to_qfloat(const QObject *obj);
+void qfloat_destroy_obj(QObject *obj);
 
 #endif /* QFLOAT_H */

include/qapi/qmp/qint.h

@@ -24,5 +24,6 @@ typedef struct QInt {
 QInt *qint_from_int(int64_t value);
 int64_t qint_get_int(const QInt *qi);
 QInt *qobject_to_qint(const QObject *obj);
+void qint_destroy_obj(QObject *obj);
 
 #endif /* QINT_H */

include/qapi/qmp/qlist.h

@@ -49,6 +49,7 @@ QObject *qlist_peek(QList *qlist);
 int qlist_empty(const QList *qlist);
 size_t qlist_size(const QList *qlist);
 QList *qobject_to_qlist(const QObject *obj);
+void qlist_destroy_obj(QObject *obj);
 
 static inline const QListEntry *qlist_first(const QList *qlist)
 {

include/qapi/qmp/qobject.h

@@ -47,15 +47,8 @@ typedef enum {
     QTYPE_MAX,
 } qtype_code;
 
-struct QObject;
-
-typedef struct QType {
-    qtype_code code;
-    void (*destroy)(struct QObject *);
-} QType;
-
 typedef struct QObject {
-    const QType *type;
+    qtype_code type;
     size_t refcnt;
 } QObject;
 
@@ -71,9 +64,12 @@ typedef struct QObject {
     qobject_decref(obj ? QOBJECT(obj) : NULL)
 
 /* Initialize an object to default values */
-#define QOBJECT_INIT(obj, qtype_type)   \
-    obj->base.refcnt = 1;               \
-    obj->base.type   = qtype_type
+static inline void qobject_init(QObject *obj, qtype_code type)
+{
+    assert(QTYPE_NONE < type && type < QTYPE_MAX);
+    obj->refcnt = 1;
+    obj->type = type;
+}
 
 /**
  * qobject_incref(): Increment QObject's reference count
@@ -84,6 +80,11 @@ static inline void qobject_incref(QObject *obj)
         obj->refcnt++;
 }
 
+/**
+ * qobject_destroy(): Free resources used by the object
+ */
+void qobject_destroy(QObject *obj);
+
 /**
  * qobject_decref(): Decrement QObject's reference count, deallocate
  * when it reaches zero
@@ -92,9 +93,7 @@ static inline void qobject_decref(QObject *obj)
 {
     assert(!obj || obj->refcnt);
     if (obj && --obj->refcnt == 0) {
-        assert(obj->type != NULL);
-        assert(obj->type->destroy != NULL);
-        obj->type->destroy(obj);
+        qobject_destroy(obj);
     }
 }
 
@@ -103,8 +102,8 @@ static inline void qobject_decref(QObject *obj)
  */
 static inline qtype_code qobject_type(const QObject *obj)
 {
-    assert(obj->type != NULL);
-    return obj->type->code;
+    assert(QTYPE_NONE < obj->type && obj->type < QTYPE_MAX);
+    return obj->type;
 }
 
 extern QObject qnull_;

include/qapi/qmp/qstring.h

@@ -32,5 +32,6 @@ void qstring_append_int(QString *qstring, int64_t value);
 void qstring_append(QString *qstring, const char *str);
 void qstring_append_chr(QString *qstring, int c);
 QString *qobject_to_qstring(const QObject *obj);
+void qstring_destroy_obj(QObject *obj);
 
 #endif /* QSTRING_H */

qobject/Makefile.objs

@@ -1,2 +1,2 @@
 util-obj-y = qnull.o qint.o qstring.o qdict.o qlist.o qfloat.o qbool.o
-util-obj-y += qjson.o json-lexer.o json-streamer.o json-parser.o
+util-obj-y += qjson.o qobject.o json-lexer.o json-streamer.o json-parser.o

qobject/qbool.c

@@ -15,13 +15,6 @@
 #include "qapi/qmp/qobject.h"
 #include "qemu-common.h"
 
-static void qbool_destroy_obj(QObject *obj);
-
-static const QType qbool_type = {
-    .code = QTYPE_QBOOL,
-    .destroy = qbool_destroy_obj,
-};
-
 /**
  * qbool_from_bool(): Create a new QBool from a bool
  *
@@ -32,8 +25,8 @@ QBool *qbool_from_bool(bool value)
     QBool *qb;
 
     qb = g_malloc(sizeof(*qb));
+    qobject_init(QOBJECT(qb), QTYPE_QBOOL);
     qb->value = value;
-    QOBJECT_INIT(qb, &qbool_type);
 
     return qb;
 }
@@ -61,7 +54,7 @@ QBool *qobject_to_qbool(const QObject *obj)
  * qbool_destroy_obj(): Free all memory allocated by a
  * QBool object
  */
-static void qbool_destroy_obj(QObject *obj)
+void qbool_destroy_obj(QObject *obj)
 {
     assert(obj != NULL);
     g_free(qobject_to_qbool(obj));

qobject/qdict.c

@@ -19,13 +19,6 @@
 #include "qemu/queue.h"
 #include "qemu-common.h"
 
-static void qdict_destroy_obj(QObject *obj);
-
-static const QType qdict_type = {
-    .code = QTYPE_QDICT,
-    .destroy = qdict_destroy_obj,
-};
-
 /**
  * qdict_new(): Create a new QDict
  *
@@ -36,7 +29,7 @@ QDict *qdict_new(void)
     QDict *qdict;
 
     qdict = g_malloc0(sizeof(*qdict));
-    QOBJECT_INIT(qdict, &qdict_type);
+    qobject_init(QOBJECT(qdict), QTYPE_QDICT);
 
     return qdict;
 }
@@ -441,7 +434,7 @@ void qdict_del(QDict *qdict, const char *key)
 /**
  * qdict_destroy_obj(): Free all the memory allocated by a QDict
  */
-static void qdict_destroy_obj(QObject *obj)
+void qdict_destroy_obj(QObject *obj)
 {
     int i;
     QDict *qdict;

qobject/qfloat.c

@@ -15,13 +15,6 @@
 #include "qapi/qmp/qobject.h"
 #include "qemu-common.h"
 
-static void qfloat_destroy_obj(QObject *obj);
-
-static const QType qfloat_type = {
-    .code = QTYPE_QFLOAT,
-    .destroy = qfloat_destroy_obj,
-};
-
 /**
  * qfloat_from_int(): Create a new QFloat from a float
  *
@@ -32,8 +25,8 @@ QFloat *qfloat_from_double(double value)
     QFloat *qf;
 
     qf = g_malloc(sizeof(*qf));
+    qobject_init(QOBJECT(qf), QTYPE_QFLOAT);
     qf->value = value;
-    QOBJECT_INIT(qf, &qfloat_type);
 
     return qf;
 }
@@ -61,7 +54,7 @@ QFloat *qobject_to_qfloat(const QObject *obj)
  * qfloat_destroy_obj(): Free all memory allocated by a
  * QFloat object
  */
-static void qfloat_destroy_obj(QObject *obj)
+void qfloat_destroy_obj(QObject *obj)
 {
     assert(obj != NULL);
     g_free(qobject_to_qfloat(obj));

qobject/qint.c

@@ -14,13 +14,6 @@
 #include "qapi/qmp/qobject.h"
 #include "qemu-common.h"
 
-static void qint_destroy_obj(QObject *obj);
-
-static const QType qint_type = {
-    .code = QTYPE_QINT,
-    .destroy = qint_destroy_obj,
-};
-
 /**
  * qint_from_int(): Create a new QInt from an int64_t
  *
@@ -31,8 +24,8 @@ QInt *qint_from_int(int64_t value)
     QInt *qi;
 
     qi = g_malloc(sizeof(*qi));
+    qobject_init(QOBJECT(qi), QTYPE_QINT);
     qi->value = value;
-    QOBJECT_INIT(qi, &qint_type);
 
     return qi;
 }
@@ -60,7 +53,7 @@ QInt *qobject_to_qint(const QObject *obj)
  * qint_destroy_obj(): Free all memory allocated by a
  * QInt object
  */
-static void qint_destroy_obj(QObject *obj)
+void qint_destroy_obj(QObject *obj)
 {
     assert(obj != NULL);
     g_free(qobject_to_qint(obj));

qobject/qlist.c

@@ -15,13 +15,6 @@
 #include "qemu/queue.h"
 #include "qemu-common.h"
 
-static void qlist_destroy_obj(QObject *obj);
-
-static const QType qlist_type = {
-    .code = QTYPE_QLIST,
-    .destroy = qlist_destroy_obj,
-};
- 
 /**
  * qlist_new(): Create a new QList
  *
@@ -32,8 +25,8 @@ QList *qlist_new(void)
     QList *qlist;
 
     qlist = g_malloc(sizeof(*qlist));
+    qobject_init(QOBJECT(qlist), QTYPE_QLIST);
     QTAILQ_INIT(&qlist->head);
-    QOBJECT_INIT(qlist, &qlist_type);
 
     return qlist;
 }
@@ -151,7 +144,7 @@ QList *qobject_to_qlist(const QObject *obj)
 /**
  * qlist_destroy_obj(): Free all the memory allocated by a QList
  */
-static void qlist_destroy_obj(QObject *obj)
+void qlist_destroy_obj(QObject *obj)
 {
     QList *qlist;
     QListEntry *entry, *next_entry;

qobject/qnull.c

@@ -13,17 +13,7 @@
 #include "qemu-common.h"
 #include "qapi/qmp/qobject.h"
 
-static void qnull_destroy_obj(QObject *obj)
-{
-    assert(0);
-}
-
-static const QType qnull_type = {
-    .code = QTYPE_QNULL,
-    .destroy = qnull_destroy_obj,
-};
-
 QObject qnull_ = {
-    .type = &qnull_type,
+    .type = QTYPE_QNULL,
     .refcnt = 1,
 };

qobject/qobject.c

@@ -0,0 +1,34 @@
+/*
+ * QObject
+ *
+ * Copyright (C) 2015 Red Hat, Inc.
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1
+ * or later.  See the COPYING.LIB file in the top-level directory.
+ */
+
+#include "qemu-common.h"
+#include "qapi/qmp/qbool.h"
+#include "qapi/qmp/qdict.h"
+#include "qapi/qmp/qfloat.h"
+#include "qapi/qmp/qint.h"
+#include "qapi/qmp/qlist.h"
+#include "qapi/qmp/qstring.h"
+
+static void (*qdestroy[QTYPE_MAX])(QObject *) = {
+    [QTYPE_NONE] = NULL,               /* No such object exists */
+    [QTYPE_QNULL] = NULL,              /* qnull_ is indestructible */
+    [QTYPE_QINT] = qint_destroy_obj,
+    [QTYPE_QSTRING] = qstring_destroy_obj,
+    [QTYPE_QDICT] = qdict_destroy_obj,
+    [QTYPE_QLIST] = qlist_destroy_obj,
+    [QTYPE_QFLOAT] = qfloat_destroy_obj,
+    [QTYPE_QBOOL] = qbool_destroy_obj,
+};
+
+void qobject_destroy(QObject *obj)
+{
+    assert(!obj->refcnt);
+    assert(QTYPE_QNULL < obj->type && obj->type < QTYPE_MAX);
+    qdestroy[obj->type](obj);
+}

qobject/qstring.c

@@ -14,13 +14,6 @@
 #include "qapi/qmp/qstring.h"
 #include "qemu-common.h"
 
-static void qstring_destroy_obj(QObject *obj);
-
-static const QType qstring_type = {
-    .code = QTYPE_QSTRING,
-    .destroy = qstring_destroy_obj,
-};
-
 /**
  * qstring_new(): Create a new empty QString
  *
@@ -49,6 +42,7 @@ QString *qstring_from_substr(const char *str, int start, int end)
     QString *qstring;
 
     qstring = g_malloc(sizeof(*qstring));
+    qobject_init(QOBJECT(qstring), QTYPE_QSTRING);
 
     qstring->length = end - start + 1;
     qstring->capacity = qstring->length;
@@ -57,7 +51,6 @@ QString *qstring_from_substr(const char *str, int start, int end)
     memcpy(qstring->string, str + start, qstring->length);
     qstring->string[qstring->length] = 0;
 
-    QOBJECT_INIT(qstring, &qstring_type);
 
     return qstring;
 }
@@ -138,7 +131,7 @@ const char *qstring_get_str(const QString *qstring)
  * qstring_destroy_obj(): Free all memory allocated by a QString
  * object
  */
-static void qstring_destroy_obj(QObject *obj)
+void qstring_destroy_obj(QObject *obj)
 {
     QString *qs;