如何进行线程安全的字典操作

Question

如何以线程安全的方式操作字典，我想将字典存储到 2 个具有不同字典值的不同队列（操作前 1 个，操作后 1 个）但结果是它们都在操作后存储字典。

这是我的代码

from threading import Timer, Lock
from queue import Queue

q = Queue(maxsize=10000)
k = Queue(maxsize=10000)
k_lock = Lock()
q_lock = Lock()
def write_func(x):
    rows = []
    while not x.empty():
        rows.append(x.get())
    if len(rows) == 0:
        return
    print('A Row is {} and total A row is {}'.format(rows, len(rows)))

def write_k(x):
    rows = []
    while not x.empty():
        rows.append(x.get())
    if len(rows) == 0:
        return
    print('B Row is {} and total B row is {}'.format(rows, len(rows)))


def write_caller(sec=10):
    write_func(q)
    Timer(sec, write_caller, [sec]).start()


def k_caller(sec=1):
    write_k(k)
    Timer(sec, k_caller, [sec]).start()


write_caller()
k_caller()
while True:
    val = {"event": "lazada"}
    k.put(val)
    q_val = val
    with Lock():
        q_val["dt"] = "2018-04-11"
        q.put(q_val)
    if q.qsize() >= 10:
        write_func(q)

上面代码的结果是这样的

A Row is [{'event': 'lazada', 'dt': '2018-04-11'}, ...]
B Row is [{'event': 'lazada', 'dt': '2018-04-11'}, ...]

但我希望 B 行只包含 'event' 而没有 'dt'。这就是我想要的

A Row is [{'event': 'lazada', 'dt': '2018-04-11'}, ...]
B Row is [{'event': 'lazada'}, ...]

Answer 1

当您执行 q_val = val 时，您复制的是字典的引用，您并未创建变量的副本。所以q_val和val其实是同一个字典

Assignment statements in Python do not copy objects, they create bindings between a target and an object

如果要复制 python 中的变量，请使用 copy.copy()。

q_val = copy.copy(val)

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