I'm writing a C program in which I need to pass messages between child processes and the main process. But the thing is, I need to do it without using the functions like msgget() and msgsnd()

How can I implement? What kind of techniques can I use?

CodePudding user response：

There are multiple ways to communicate with children processes, it depends on your application.

Very much depends on the level of abstraction of your application.

-- If the level of abstraction is low:

If you need very fast communication, you could use shared memory (e.g. shm_open()). But that would be complicated to synchronize correctly.

The most used method, and the method I'd use if I were in your shoes is: pipes. It's simple, fast, and since pipes file descriptors are supported by epoll() and those kind of asynchronous I/O APIs, you can take advantage from this fact.

Another plus is that, if your application grows, and you need to communicate with remote processes (processes that are not in your local machine), adapting pipes to sockets is very easy, basically it's still the same reading/writing from/to a file descriptor.

Also, Unix-domain sockets (which in other platforms are called "named pipes") let you to have a server process that creates a listening socket with a very well known name (e.g. an entry in the filesystem, such as /tmp/my_socket) and all clients in the local machine can connect to that.

Pipes, networking sockets, or unix-domain sockets are very interchangeable solutions, because - as said before - all involve reading/writing data from/to a file descriptor, so you can reuse the code.

The disadvantage with a file descriptor is that you're writing data to a stream of bytes, so you need to implement the "message streaming protocol" of your messages by yourself, to "unstream" your messages (marshalling/unmarshalling), but that's not so complicated in the most of the cases, and that also depends on the kind of messages you're sending.

I'd pass on other solutions such as memory mapped files and so on.

-- If the level of abstraction is higher:

You could use a 3rd party message passing system, such as RabbitMQ, ZMQ, and so on.