import json
import logging
import multiprocessing
import time
from multiprocessing import shared_memory


class SharedMemoryObj:
    def __init__(self, name='shm_0', size=5*1024*1024):
        try:
            self.shm = shared_memory.SharedMemory(name=name, create=True, size=size)  # 尝试创建共享内存，若失败则映射同名内存空间
        except:
            self.shm = shared_memory.SharedMemory(name=name, create=False)

        self.shm_name = self.shm.name
        self.length = 0
        self.contentbegin = 0

    def write(self, obj) -> bool:
        """
        将待写内容通过Json序列化，写入共享内存。
        写入格式：内容长度 + ~ + 内容
        Args:
            obj: 待写内容

        Returns:

        """
        try:
            if obj is not None:
                obj_str = json.dumps(obj)
                obj_len = len(obj_str)
                content = str(obj_len) + "~" + obj_str
                b = content.encode()
                self.shm.buf[0:len(b)] = b
                return True
            else:
                return False
        except Exception as e:
            logging.exception(e)
            return False

    def read(self) -> dict:
        """
        读取共享内存，返回字典格式内容
        Returns:dict

        """
        try:
            s = bytes(self.shm.buf[:20])
            index = str(s, 'utf-8').find("~")
            if index != -1:
                head = s[0:index]
                contentlength = int(head)
                content = bytes(self.shm.buf[index + 1:index + 1 + contentlength]).decode('utf-8')
                obj = json.loads(content, object_hook=lambda d: {int(k) if k.lstrip('-').isdigit() else k: v for k, v in
                                                                 d.items()})
                # obj = json.loads(content)
                return obj
            else:
                return {}
        except Exception as e:
            logging.exception(e)
            return {}

    def update(self, obj):
        org_obj = self.read()
        org_obj.update(obj)
        self.write(org_obj)

def test_p1():
        shareObj = SharedMemoryObj()
        while True:
            print("读取到内容：", shareObj.read())
            time.sleep(1)


def test_p2():
        shareObj = SharedMemoryObj()
        index = 0
        while True:
            index += 1
            shareObj.write([index])
            time.sleep(1)

if __name__ == '__main__':



    p1 = multiprocessing.Process(target=test_p1)
    p2 = multiprocessing.Process(target=test_p2)

    p1.start()
    p2.start()
    while True:
        time.sleep(1)