Python虚拟机之函数机制（一）

typedef struct {
    PyObject_HEAD
    PyObject *func_code;	//编译后的PyCodeObject对象
    PyObject *func_globals;	//函数运行时的global名字空间
    PyObject *func_defaults;	//默认参数（tupple或NULL）
    PyObject *func_closure;	//NULL or a tuple of cell objects，用于实现closure(闭包)
    PyObject *func_doc;		//函数的文档（PyStringObject）
    PyObject *func_name;	//函数名称，函数的__name__属性，（PyStringObject）
    PyObject *func_dict;	//函数的__dict__属性（PyDictObject或NULL）
    PyObject *func_weakreflist;	
    PyObject *func_module;	//函数的__module__，可以是任何对象
} PyFunctionObject;

# cat demo.py
def f():
    print("Function")


f()

# python2.5
……
>>> source = open("demo.py").read()
>>> co = compile(source, "demo.py", "exec")
>>> import dis
>>> dis.dis(co)
  1           0 LOAD_CONST               0 (<code object f at 0x7fd9831c3648, file "demo.py", line 1>)
              3 MAKE_FUNCTION            0
              6 STORE_NAME               0 (f)

  5           9 LOAD_NAME                0 (f)
             12 CALL_FUNCTION            0
             15 POP_TOP             
             16 LOAD_CONST               1 (None)
             19 RETURN_VALUE        
>>> from demo import f
Function
>>> dis.dis(f)
  2           0 LOAD_CONST               1 (‘Function‘)
              3 PRINT_ITEM          
              4 PRINT_NEWLINE       
              5 LOAD_CONST               0 (None)
              8 RETURN_VALUE 

case MAKE_FUNCTION:
	v = POP(); //获得与函数f对应的PyCodeObject
	x = PyFunction_New(v, f->f_globals);
	Py_DECREF(v);
	//处理函数参数的默认值
	if (x != NULL && oparg > 0)
	{
		v = PyTuple_New(oparg);
		if (v == NULL)
		{
			Py_DECREF(x);
			x = NULL;
			break;
		}
		while (--oparg >= 0)
		{
			w = POP();
			PyTuple_SET_ITEM(v, oparg, w);
		}
		err = PyFunction_SetDefaults(x, v);
		Py_DECREF(v);
	}
	PUSH(x);
	break;

PyObject * PyFunction_New(PyObject *code, PyObject *globals)
{
	//[1]：申请PyFunctionObject对象所需的内存空间
	PyFunctionObject *op = PyObject_GC_New(PyFunctionObject, &PyFunction_Type);
	static PyObject *__name__ = 0;
	if (op != NULL) {
		……
		//设置PyCodeObject对象
		op->func_code = code;
		//设置global名字空间
		op->func_globals = globals;
		//设置函数名
		op->func_name = ((PyCodeObject *)code)->co_name;
		Py_INCREF(op->func_name);
		op->func_defaults = NULL; /* No default arguments */
		op->func_closure = NULL;
		//函数中的常量对象表
		consts = ((PyCodeObject *)code)->co_consts;
		//函数文档
		if (PyTuple_Size(consts) >= 1) {
			doc = PyTuple_GetItem(consts, 0);
			if (!PyString_Check(doc) && !PyUnicode_Check(doc))
				doc = Py_None;
		}
		else
			doc = Py_None;
		……
	}
	else
		return NULL;
	_PyObject_GC_TRACK(op);
	return (PyObject *)op;
}

case CALL_FUNCTION:
	{
		PyObject **sp;
		PCALL(PCALL_ALL);
		sp = stack_pointer;
		x = call_function(&sp, oparg);
		stack_pointer = sp;
		PUSH(x);
		if (x != NULL)
			continue;
		break;
	}

static PyObject * call_function(PyObject ***pp_stack, int oparg)
{
	//[1]：处理函数参数信息
	int na = oparg & 0xff;
	int nk = (oparg >> 8) & 0xff;
	int n = na + 2 * nk;
	//[2]：获得PyFunctionObject对象
	PyObject **pfunc = (*pp_stack) - n - 1;
	PyObject *func = *pfunc;
	PyObject *x, *w;

	if (PyCFunction_Check(func) && nk == 0)
	{
		……
	}
	else
	{
		if (PyMethod_Check(func) && PyMethod_GET_SELF(func) != NULL)
		{
			……
		}
		else
			Py_INCREF(func);
		READ_TIMESTAMP(*pintr0);
		//[3]：对PyFunctionObject对象进行调用
		if (PyFunction_Check(func))
			x = fast_function(func, pp_stack, n, na, nk);
		else
			x = do_call(func, pp_stack, na, nk);
		……
	}

	……
	return x;
}

static PyObject * fast_function(PyObject *func, PyObject ***pp_stack, int n, int na, int nk)
{
	PyCodeObject *co = (PyCodeObject *)PyFunction_GET_CODE(func);
	PyObject *globals = PyFunction_GET_GLOBALS(func);
	PyObject *argdefs = PyFunction_GET_DEFAULTS(func);
	PyObject **d = NULL;
	int nd = 0;
	
	……
	//[1]：一般函数的快速通道
	if (argdefs == NULL && co->co_argcount == n && nk == 0 &&
		co->co_flags == (CO_OPTIMIZED | CO_NEWLOCALS | CO_NOFREE))
	{
		PyFrameObject *f;
		PyObject *retval = NULL;
		PyThreadState *tstate = PyThreadState_GET();
		PyObject **fastlocals, **stack;
		int i;
		……
		f = PyFrame_New(tstate, co, globals, NULL);
		……
		//再次进入Python虚拟机
		retval = PyEval_EvalFrameEx(f, 0);
		……
		return retval;
	}
	if (argdefs != NULL)
	{
		d = &PyTuple_GET_ITEM(argdefs, 0);
		nd = ((PyTupleObject *)argdefs)->ob_size;
	}
	//PyEval_EvalCodeEx的实现中，依然会调用PyEval_EvalFrameEx
	return PyEval_EvalCodeEx(co, globals,
							 (PyObject *)NULL, (*pp_stack) - n, na,
							 (*pp_stack) - 2 * nk, nk, d, nd,
							 PyFunction_GET_CLOSURE(func));
}