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

// Copyright (c) 2017-present PyO3 Project and Contributors

//! Free allocation list

use crate::ffi;
use crate::type_object::{pytype_drop, PyObjectAlloc, PyTypeInfo};
use crate::Python;
use std::mem;
use std::os::raw::c_void;

/// Implementing this trait for custom class adds free allocation list to class.
/// The performance improvement applies to types that are often created and deleted in a row,
/// so that they can benefit from a freelist.
pub trait PyObjectWithFreeList: PyTypeInfo {
    fn get_free_list() -> &'static mut FreeList<*mut ffi::PyObject>;
}

pub enum Slot<T> {
    Empty,
    Filled(T),
}

pub struct FreeList<T> {
    entries: Vec<Slot<T>>,
    split: usize,
    capacity: usize,
}

impl<T> FreeList<T> {
    /// Create new `FreeList` instance with specified capacity
    pub fn with_capacity(capacity: usize) -> FreeList<T> {
        let entries = (0..capacity).map(|_| Slot::Empty).collect::<Vec<_>>();

        FreeList {
            entries,
            split: 0,
            capacity,
        }
    }

    /// Pop first non empty item
    pub fn pop(&mut self) -> Option<T> {
        let idx = self.split;
        if idx == 0 {
            None
        } else {
            match mem::replace(&mut self.entries[idx - 1], Slot::Empty) {
                Slot::Filled(v) => {
                    self.split = idx - 1;
                    Some(v)
                }
                _ => panic!("FreeList is corrupt"),
            }
        }
    }

    /// Insert a value into the list
    pub fn insert(&mut self, val: T) -> Option<T> {
        let next = self.split + 1;
        if next < self.capacity {
            self.entries[self.split] = Slot::Filled(val);
            self.split = next;
            None
        } else {
            Some(val)
        }
    }
}

impl<T> PyObjectAlloc for T
where
    T: PyObjectWithFreeList,
{
    unsafe fn alloc(_py: Python) -> *mut ffi::PyObject {
        if let Some(obj) = <Self as PyObjectWithFreeList>::get_free_list().pop() {
            ffi::PyObject_Init(obj, <Self as PyTypeInfo>::type_object());
            obj
        } else {
            ffi::PyType_GenericAlloc(<Self as PyTypeInfo>::type_object(), 0)
        }
    }

    #[cfg(Py_3)]
    unsafe fn dealloc(py: Python, obj: *mut ffi::PyObject) {
        pytype_drop::<Self>(py, obj);

        if ffi::PyObject_CallFinalizerFromDealloc(obj) < 0 {
            return;
        }

        if let Some(obj) = <Self as PyObjectWithFreeList>::get_free_list().insert(obj) {
            match Self::type_object().tp_free {
                Some(free) => free(obj as *mut c_void),
                None => {
                    let ty = ffi::Py_TYPE(obj);
                    if ffi::PyType_IS_GC(ty) != 0 {
                        ffi::PyObject_GC_Del(obj as *mut c_void);
                    } else {
                        ffi::PyObject_Free(obj as *mut c_void);
                    }

                    // For heap types, PyType_GenericAlloc calls INCREF on the type objects,
                    // so we need to call DECREF here:
                    if ffi::PyType_HasFeature(ty, ffi::Py_TPFLAGS_HEAPTYPE) != 0 {
                        ffi::Py_DECREF(ty as *mut ffi::PyObject);
                    }
                }
            }
        }
    }

    #[cfg(not(Py_3))]
    unsafe fn dealloc(py: Python, obj: *mut ffi::PyObject) {
        pytype_drop::<Self>(py, obj);

        if let Some(obj) = <Self as PyObjectWithFreeList>::get_free_list().insert(obj) {
            match Self::type_object().tp_free {
                Some(free) => free(obj as *mut c_void),
                None => {
                    let ty = ffi::Py_TYPE(obj);
                    if ffi::PyType_IS_GC(ty) != 0 {
                        ffi::PyObject_GC_Del(obj as *mut c_void);
                    } else {
                        ffi::PyObject_Free(obj as *mut c_void);
                    }

                    // For heap types, PyType_GenericAlloc calls INCREF on the type objects,
                    // so we need to call DECREF here:
                    if ffi::PyType_HasFeature(ty, ffi::Py_TPFLAGS_HEAPTYPE) != 0 {
                        ffi::Py_DECREF(ty as *mut ffi::PyObject);
                    }
                }
            }
        }
    }
}