CPython学习笔记01

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import sys

a = 10
b = "李忠鹏"

print(type(a)) # <class 'int'>
print(sys.getsizeof(a)) # 14 bytes

print(type(b)) # <class 'str'>
print(sys.getsizeof(b)) # 44 bytes

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// Include/object.h
// 开启GIL锁的PyObject结构体
#ifdef _Py_OPAQUE_PYOBJECT
  /* PyObject is opaque */
#elif !defined(Py_GIL_DISABLED)
struct _object {
    _Py_ANONYMOUS union {
#if SIZEOF_VOID_P > 4 // 64位
        PY_INT64_T ob_refcnt_full; /* This field is needed for efficient initialization with Clang on ARM */
        struct {
#  if PY_BIG_ENDIAN
            uint16_t ob_flags;
            uint16_t ob_overflow;
            uint32_t ob_refcnt;
#  else 
            uint32_t ob_refcnt; // 引用计数器
            uint16_t ob_overflow; // 计数溢出标记
            uint16_t ob_flags; // 标志是否被GC回收
#  endif
        };
#else // 32位
        Py_ssize_t ob_refcnt;
#endif
        _Py_ALIGNED_DEF(_PyObject_MIN_ALIGNMENT, char) _aligner;
    };

    PyTypeObject *ob_type;
};

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// PyLongObject整数对象
typedef struct _PyLongValue {
    uintptr_t lv_tag; /* Number of digits, sign and flags */
    digit ob_digit[1];
} _PyLongValue;

struct _longobject {
    PyObject_HEAD // 宏展开为PyObject ob_base
    _PyLongValue long_value;  // 值
};

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a = 1
b = 1

# is用于判断两个栈变量是否是否指向同一个堆地址
print (a is b)  # True

# id函数也可以用来获取所指对象的地址
print(id(a) == id(b)) # True

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import dis

code = """
c = 2577
d = 2577
print(c is d)
print(id(c), id(d))
"""

dis.dis(code)

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2           0 LOAD_CONST               0 (2577)
              2 STORE_NAME               0 (c)

  3           4 LOAD_CONST               0 (2577)
              6 STORE_NAME               1 (d)

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// Python/ceval_gil.c

// 获得锁
#endif
    /* We now hold the GIL */
    _Py_atomic_store_int_relaxed(&gil->locked, 1);
    _Py_ANNOTATE_RWLOCK_ACQUIRED(&gil->locked, /*is_write=*/1);

    if (tstate != (PyThreadState*)_Py_atomic_load_ptr_relaxed(&gil->last_holder)) {
        _Py_atomic_store_ptr_relaxed(&gil->last_holder, tstate);
        ++gil->switch_number;
    }

// 锁被占有，请求释放锁
    _Py_set_eval_breaker_bit(holder_tstate, _PY_GIL_DROP_REQUEST_BIT);
    drop_requested = 1;

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import threading
import time

def count_task(n):
    result = 0
    for i in range(n):
        result += i
    return result

# 单线程执行
def single_thread(n):
    start = time.time()
    count_task(n)
    end = time.time()
    return end - start

# 多线程执行（4个线程）
def multi_thread(n):
    threads = []
    task_per_thread = n // 4
    start = time.time()
    
    for _ in range(4):
        t = threading.Thread(target=count_task, args=(task_per_thread,))
        threads.append(t)
        t.start()
    
    # 等待所有线程完成
    for t in threads:
        t.join()
    
    end = time.time()
    return end - start

if __name__ == "__main__":
    total_iterations = 10**8
    
    single_time = single_thread(total_iterations)
    print(f"单线程耗时：{single_time:.2f}秒") # 单线程耗时：6.43秒

    multi_time = multi_thread(total_iterations)
    print(f"4线程耗时：{multi_time:.2f}秒") # 4线程耗时：6.75秒

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import sys
import gc

gc.disable() # 禁用GC，只依赖计数器

a = [1, 2, 3]
b = [4, 5, 6]

print(sys.getrefcount(a) - 1) # 1
print(sys.getrefcount(b) - 1) # 1

a.append(b)
b.append(a)

print(sys.getrefcount(a) - 1) # 2
print(sys.getrefcount(b) - 1) # 2

"""
此时执行del a del b，但是计数结果仍不为0，实际上未收回
"""
del a # 1 
del b # 1