forkとpipeとepollのサンプルコード

main.py

import os
import sys
import time
import select

READ_ONLY = select.EPOLLIN

def main():
    read_fd, write_fd = os.pipe2(os.O_NONBLOCK)
    pid = os.fork()
    if pid:
        print("子PID: {}".format(pid))
        # 親
        os.close(read_fd)
        write_pipe = os.fdopen(write_fd, 'wb')
        for bit in b"hello":
            time.sleep(2)
            write_pipe.write(bytes([bit]))
            write_pipe.flush()
        write_pipe.close()
        print("--end parent--")
    else:
        # 子
        os.close(write_fd)
        read_pipe = os.fdopen(read_fd, 'rb')
        poller = select.epoll()
        poller.register(read_fd, READ_ONLY)
        bytes_read = 0
        content = b""
        done = False
        while True:
            events = poller.poll()
            print(events)
            for fd, event in events:
                if fd != read_fd:
                    continue
                read_data = read_pipe.read()
                if read_data:
                    bytes_read += len(read_data)
                    print("読めた: {}".format(bytes_read))
                    content += read_data
                if bytes_read >= 5:
                    done = True
                    break
            if done:
                break
        read_pipe.close()
        print(content)
        print("--end child--")

main()