后台传输到标准输出

Question

I have the following scheme:

\
 + granpa
    |
    +--- uncle
    |
    +--- dad
          |
          +--- son1
          +--- son2
          +--- son3

Uncle should be the only one controlling output, so I thought of using a pipe() created by granpa and shared with sons across fork() . So far so good.

The problem is that uncle also reads from a System V Message Queue ( msgget() ) in a infinite loop, hence acting as a server.

My problem is: in a scenario where we don't have multi-threading, how can these operations be done at the same time?

A couple of solutions that came to my mind include:

1. dup -ing pipe to standard output using dup2() , but it didn't work for unknown reasons; I guess it's because the kernel doesn't automatically copy data from pipe buffer to terminal output memory, that would be too cool.
2. Background copying data from pipe buffer with splice() or tee() , but it looks like they are all blocking and won't execute in background (or perhaps they do and I'm doing something wrong).
3. Using select() to determine at every cycle if I have a message or something to print, but unfortunately System V Message Queues aren't file descriptors in the Linux kernel (and I have no plans to make a custom version of the kernel as someone on the internet did exactly for this issue, absolutely).

Another bunch of solutions that could actually work but kinda break the logic are:

4. Using only a System V Message Queue with a very big struct and using the msgtype field to determine whether I'm asking for something or want to print something. Awful.
5. Insted of using a System V Message Queue, use a socketpair() and the do select() or poll() or whatever. This is my final solution, but if someone knows how to do it with System V Message Queues its preferred.

Answer 1

You could try looking into the Linux D-Bus . It was met to simplify large multi piped projects like this and give the client program much less lines to work with.