Py + gi 高效 c 庫整合方案

Py + GI
⾼高效 C 庫整合⽅方案
Derek 呆

北京/上海/⼲⼴广州 0xFF Life's pathetic, go Pythonic!
● Derek 呆
○ dailidu@linuxdeepin.com
○ daiderek@gmail.com
● 來⾃自 Linux Deepin
● 慣 C
● 愛 Python
● 搞 BASH
● 編 Linux System Program

Python <= (Binding) => C

⼿手寫, 費時, 易出錯, 重複造輪

想⽤用⼯工具代勞?

試試 PyGObject

基於 GObject Introspection (GI)

與 Python 間只有少量整合代碼

⾃自源代碼⽣生成 Type Library

包含 Version, Function Signature,
Type Information, ...

可於多語⾔言間共⽤用

Runtime 時配合 libffi 進⾏行調⽤用

易於將成果推送到 Upstream

準備⼯工作
$ apt-get install build-essential
gobject-introspection
python-gobject
libglib2.0-dev
gtk-doc-tools

例 1
/* mylib.h */
#ifndef __MYLIB_H_
#define __MYLIB_H_
void hello();
#endif /* __MYLIB_H_ */

例 1
/* mylib.c */
#include "mylib.h"
#include <stdio.h>
void hello()
{
printf("hellon");
}

例 1
$ gcc -o libmylib.so -share …
$ g-ir-scanner -o MyLib-1.0.gir
-lmylib
-L.
mylib.h
…
$ g-ir-compiler MyLib-1.0.gir >MyLib-1.0.typelib

例 1
...
<namespace name="MyLib"
version="1.0"
shared-library="libmylib.so"
c:identifier-prefixes="MyLib"
c:symbol-prefixes="my_lib">
<function name="hello" c:identifier="hello">
<return-value transfer-ownership="none">
<type name="none" c:type="void"/>
</return-value>
</function>
</namespace>
...

例 1
$ python -c 'from gi.repository import
MyLib; MyLib.hello()'
hello

資源管理是 Binding 開發⼀一⼤大重點

否則 Resource Leaking, Double Free,
Invalid FD, Bus Error, Segfault...

例 2
/* mylib.h */
#ifndef __MYLIB_H_
#define __MYLIB_H_
const char * hello3();
char * hello2();

例 2
/* mylib.c */
#include "mylib.h"
#include <stdio.h>
#include <string.h>
const char * hello3()
{
return "hello";
}
char * hello2()
{
return strdup("hello");
}

例 2
...
<function name="hello2" c:identifier="hello2">
<return-value transfer-ownership="full">
<type name="utf8" c:type="char*"/>
</return-value>
</function>
<function name="hello3" c:identifier="hello3">
<return-value transfer-ownership="none">
<type name="utf8" c:type="const char*"/>
</return-value>
</function>
...

例 2
MyLib; print MyLib.hello2(); print
MyLib.hello3()'
hello
hello

GI 有默認資源管理策略

但可通過 Annotation 改變

例 3
#ifndef __MYLIB_H_
#define __MYLIB_H_
/**
* hello4:
* Returns: (transfer full):
*/
const char * hello4();

例 3
#include "mylib.h"
#include <stdio.h>
const char * hello4()
{
return "hello";
}

例 3
python -c 'from gi.repository import MyLib;
print MyLib.hello4()'
*** Error in `python': munmap_chunk():
invalid pointer: 0x00007f4503efd65d ***
Aborted

Out 參數能處理嗎?

例 4
/**
* hello5:
*
* @msg: (out callee-allocates):
*/
void hello5(char **msg);

例 4
void hello5(char **msg)
{
*msg = strdup("hello");
}

例 4
MyLib; print MyLib.hello5()'
hello

Out 參數會以 Return Value呈現

Struct ⼜又如何?

⼀一個 Type 需加上 4 個 Functions

基本也可以⼯工具產⽣生

例 5
#include <glib-object.h>
#define TYPE_MY_OBJ (my_obj_get_type())
typedef struct _MyObj MyObj;
MyObj my_obj_new();
GType my_obj_get_type();

例 5
struct _MyObj
{
int v;
};
MyObj * my_obj_new()
{
return malloc(sizeof(MyObj));
}

例 5
MyObj * _my_obj_copy(MyObj *self)
{
MyObj *new_self = my_obj_new();
*new_self = *self;
return new_self;
}

例 5
void _my_obj_free(MyObj *self)
{
free(self);
}

例 5
GType my_obj_get_type()
{
static GType type = 0;
if(! type) {
type = g_boxed_type_register_static(
"MyObj",
(GBoxedCopyFunc) _my_obj_copy,
(GBoxedFreeFunc) _my_obj_free);
}
return type;
}

例 5
$ python
>>> from gi.repository import MyLib
>>> o = MyLib.MyObj()
>>> o
<MyObj at 0x27d39c0>
>>> o.copy()
<MyObj at 0x2a7b7e0>
>>> o = None
>>>

還有⽀支持不了的類型嗎?

Variadic Function

⼀一些資源
●  完整內容
●  git repository
●  Annotation 參考

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