# type_object.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/pyo3-0.13.2/src/type_object.rs`.
Keywords: rust, rustlang, rust-lang

      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239

    // Copyright (c) 2017-present PyO3 Project and Contributors
    //! Python type object information

    use crate::conversion::IntoPyPointer;
    use crate::once_cell::GILOnceCell;
    use crate::pyclass::{create_type_object, py_class_attributes, PyClass};
    use crate::pyclass_init::PyObjectInit;
    use crate::types::{PyAny, PyType};
    use crate::{ffi, AsPyPointer, PyErr, PyNativeType, PyObject, PyResult, Python};
    use parking_lot::{const_mutex, Mutex};
    use std::thread::{self, ThreadId};

    /// `T: PyLayout<U>` represents that `T` is a concrete representaion of `U` in Python heap.
    /// E.g., `PyCell` is a concrete representaion of all `pyclass`es, and `ffi::PyObject`
    /// is of `PyAny`.
    ///
    /// This trait is intended to be used internally.
    pub unsafe trait PyLayout<T: PyTypeInfo> {
        const IS_NATIVE_TYPE: bool = true;
        fn get_super(&mut self) -> Option<&mut T::BaseLayout> {
            None
        }
        fn py_init(&mut self, _value: T) {}
        unsafe fn py_drop(&mut self, _py: Python) {}
    }

    /// `T: PySizedLayout<U>` represents `T` is not a instance of
    /// [`PyVarObject`](https://docs.python.org/3.8/c-api/structures.html?highlight=pyvarobject#c.PyVarObject).
    /// , in addition that `T` is a concrete representaion of `U`.
    pub trait PySizedLayout<T: PyTypeInfo>: PyLayout<T> + Sized {}

    /// Marker type indicates that `Self` can be a base layout of `PyClass`.
    ///
    /// # Safety
    ///
    /// Self should be laid out as follows:
    /// ```ignore
    /// #[repr(C)]
    /// struct Self {
    ///     obj: ffi::PyObject,
    ///     borrow_flag: u64,
    ///     ...
    /// }
    /// ```
    /// Otherwise, implementing this trait is undefined behavior.
    pub unsafe trait PyBorrowFlagLayout<T: PyTypeInfo>: PyLayout<T> + Sized {}

    /// Our custom type flags
    #[doc(hidden)]
    pub mod type_flags {
        /// Type object supports Python GC
        pub const GC: usize = 1;

        /// Type object supports Python weak references
        pub const WEAKREF: usize = 1 << 1;

        /// Type object can be used as the base type of another type
        pub const BASETYPE: usize = 1 << 2;

        /// The instances of this type have a dictionary containing instance variables
        pub const DICT: usize = 1 << 3;

        /// The class declared by #[pyclass(extends=~)]
        pub const EXTENDED: usize = 1 << 4;
    }

    /// Python type information.
    /// All Python native types(e.g., `PyDict`) and `#[pyclass]` structs implement this trait.
    ///
    /// This trait is marked unsafe because:
    ///  - specifying the incorrect layout can lead to memory errors
    ///  - the return value of type_object must always point to the same PyTypeObject instance
    pub unsafe trait PyTypeInfo: Sized {
        /// Type of objects to store in PyObject struct
        type Type;

        /// Class name
        const NAME: &'static str;

        /// Module name, if any
        const MODULE: Option<&'static str>;

        /// Class doc string
        const DESCRIPTION: &'static str = "\0";

        /// Type flags (ie PY_TYPE_FLAG_GC, PY_TYPE_FLAG_WEAKREF)
        const FLAGS: usize = 0;

        /// Base class
        type BaseType: PyTypeInfo + PyTypeObject;

        /// Layout
        type Layout: PyLayout<Self>;

        /// Layout of Basetype.
        type BaseLayout: PySizedLayout<Self::BaseType>;

        /// Initializer for layout
        type Initializer: PyObjectInit<Self>;

        /// Utility type to make Py::as_ref work
        type AsRefTarget: crate::PyNativeType;

        /// PyTypeObject instance for this type.
        fn type_object_raw(py: Python) -> *mut ffi::PyTypeObject;

        /// Checks if `object` is an instance of this type or a subclass of this type.
        fn is_type_of(object: &PyAny) -> bool {
            unsafe { ffi::PyObject_TypeCheck(object.as_ptr(), Self::type_object_raw(object.py())) != 0 }
        }

        /// Checks if `object` is an instance of this type.
        fn is_exact_type_of(object: &PyAny) -> bool {
            unsafe { ffi::Py_TYPE(object.as_ptr()) == Self::type_object_raw(object.py()) }
        }
    }

    /// Python object types that have a corresponding type object.
    ///
    /// This trait is marked unsafe because not fulfilling the contract for type_object
    /// leads to UB.
    ///
    /// See also [PyTypeInfo::type_object_raw](trait.PyTypeInfo.html#tymethod.type_object_raw).
    pub unsafe trait PyTypeObject {
        /// Returns the safe abstraction over the type object.
        fn type_object(py: Python) -> &PyType;
    }

    unsafe impl<T> PyTypeObject for T
    where
        T: PyTypeInfo,
    {
        fn type_object(py: Python) -> &PyType {
            unsafe { py.from_borrowed_ptr(Self::type_object_raw(py) as _) }
        }
    }

    /// Lazy type object for PyClass
    #[doc(hidden)]
    pub struct LazyStaticType {
        // Boxed because Python expects the type object to have a stable address.
        value: GILOnceCell<*mut ffi::PyTypeObject>,
        // Threads which have begun initialization of the `tp_dict`. Used for
        // reentrant initialization detection.
        initializing_threads: Mutex<Vec<ThreadId>>,
        tp_dict_filled: GILOnceCell<PyResult<()>>,
    }

    impl LazyStaticType {
        pub const fn new() -> Self {
            LazyStaticType {
                value: GILOnceCell::new(),
                initializing_threads: const_mutex(Vec::new()),
                tp_dict_filled: GILOnceCell::new(),
            }
        }

        pub fn get_or_init<T: PyClass>(&self, py: Python) -> *mut ffi::PyTypeObject {
            let type_object = *self.value.get_or_init(py, || {
                create_type_object::<T>(py, T::MODULE).unwrap_or_else(|e| {
                    e.print(py);
                    panic!("An error occurred while initializing class {}", T::NAME)
                })
            });

            // We might want to fill the `tp_dict` with python instances of `T`
            // itself. In order to do so, we must first initialize the type object
            // with an empty `tp_dict`: now we can create instances of `T`.
            //
            // Then we fill the `tp_dict`. Multiple threads may try to fill it at
            // the same time, but only one of them will succeed.
            //
            // More importantly, if a thread is performing initialization of the
            // `tp_dict`, it can still request the type object through `get_or_init`,
            // but the `tp_dict` may appear empty of course.

            if self.tp_dict_filled.get(py).is_some() {
                // `tp_dict` is already filled: ok.
                return type_object;
            }

            {
                let thread_id = thread::current().id();
                let mut threads = self.initializing_threads.lock();
                if threads.contains(&thread_id) {
                    // Reentrant call: just return the type object, even if the
                    // `tp_dict` is not filled yet.
                    return type_object;
                }
                threads.push(thread_id);
            }

            // Pre-compute the class attribute objects: this can temporarily
            // release the GIL since we're calling into arbitrary user code. It
            // means that another thread can continue the initialization in the
            // meantime: at worst, we'll just make a useless computation.
            let mut items = vec![];
            for attr in py_class_attributes::<T>() {
                items.push((attr.name, (attr.meth)(py)));
            }

            // Now we hold the GIL and we can assume it won't be released until we
            // return from the function.
            let result = self.tp_dict_filled.get_or_init(py, move || {
                let result = initialize_tp_dict(py, type_object as *mut ffi::PyObject, items);

                // Initialization successfully complete, can clear the thread list.
                // (No further calls to get_or_init() will try to init, on any thread.)
                *self.initializing_threads.lock() = Vec::new();
                result
            });

            if let Err(err) = result {
                err.clone_ref(py).print(py);
                panic!("An error occured while initializing `{}.__dict__`", T::NAME);
            }

            type_object
        }
    }

    fn initialize_tp_dict(
        py: Python,
        type_object: *mut ffi::PyObject,
        items: Vec<(&'static std::ffi::CStr, PyObject)>,
    ) -> PyResult<()> {
        // We hold the GIL: the dictionary update can be considered atomic from
        // the POV of other threads.
        for (key, val) in items {
            let ret = unsafe { ffi::PyObject_SetAttrString(type_object, key.as_ptr(), val.into_ptr()) };
            if ret < 0 {
                return Err(PyErr::fetch(py));
            }
        }
        Ok(())
    }

    // This is necessary for making static `LazyStaticType`s
    unsafe impl Sync for LazyStaticType {}