C++与Python命名管道通信问题：C++端无法读取响应

我的目标是通过命名管道实现Python与C++进程的同步通信，流程如下：

• C++进程通过PIPE_1发送以\n分隔的消息
• Python进程读取该消息（同样以\n分隔），并通过PIPE_2发送响应
• C++进程读取响应
• 重复上述步骤

消息包含多维数组，因此计划使用protobuf库序列化消息后写入管道。但目前C++进程在调用std::getline时阻塞，无法从PIPE_2读取数据，直到手动终止Python进程后才能获取到消息。我怀疑是缓冲问题，尝试过调用flush()以及写入\n，但均无效。

我接受其他性能足够的解决方案（需频繁往返传输消息），但希望找出问题所在。代码运行在Intel架构Mac上（最终部署环境为Linux）。

我用Python重写了C++代码的极简版本，可正常实现同步通信，无阻塞问题，往返消息耗时约10^-4秒。

最小复现代码 #

Python进程代码 #

import errno
import os

pipe1 = '/tmp/pipe1'
pipe2 = '/tmp/pipe2'
try:
    os.mkfifo(pipe1, mode=0o777)

except OSError as oe:
    if oe.errno != errno.EEXIST:
        raise

try:
    os.mkfifo(pipe2, mode=0o777)
except OSError as oe:
    if oe.errno != errno.EEXIST:
        raise


# blocks here until writer opens read_pipe
read_pipe = open(pipe1, 'r')
write_pipe = open(pipe2, 'w')
print('opened pipes')

while True:
    r = read_pipe.readline().strip('\n')
    print(f'received {r}')
    if not r:
        print("Sender terminated")
        break
    write_pipe.write(f"Response: {r}\n")
    write_pipe.flush()
    print("wrote response")

C++进程代码 #

#include <fstream>
#include <iostream>
#include <unistd.h>

int main() {
    std::string pipe1 = "/tmp/pipe1";
    std::string pipe2 = "/tmp/pipe2";

    int writes = 10;
    std::ofstream write_pipe(pipe1, std::ios::out);
    std::ifstream read_pipe(pipe2, std::ios::in);
    
    std::cout << "Opened pipes" << std::endl;
    while (writes--) {
        write_pipe << "Some useful message" << std::endl;
        printf("sent message\n");

        printf("Reading response...\n");
        std::string response;
        std::getline(read_pipe, response);
        printf("Received response: %s\n", response.c_str());
    }
    write_pipe.close();
    read_pipe.close();

    return 0;
}

可正常运行的Python版C++代码 #

import time
pipe1 = '/tmp/pipe1'
pipe2 = '/tmp/pipe2'

write_file = open(pipe1, "w")
read_file = open(pipe2, 'r')

writes = 10
while writes > 0:
    writes -= 1
    start_time = time.time()
    write_file.write("Test message" + "\n")
    write_file.flush()
    print("sent message")

    response = read_file.readline()
    end_time = time.time()
    print(f"response was {response}")

内容的提问来源于stack exchange，提问作者Jayanth