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javabeginner
javabeginner

Reputation: 41

Getting user input in 2 child processes in C

I'm just wondering if it is possible to create two children processes, and in both of these processes ask the user for input? Or would it be stuck waiting forever?

Upvotes: 0

Views: 141

Answers (1)

Nick Zavaritsky
Nick Zavaritsky

Reputation: 1489

It depends on the precise implementation of “asking user for input”. If this is readline, which implements shell-like input with the prompt and editing, it won’t work. The reason is that the library messes up with the terminal configuration. If two processes are doing the same thing simultaneously they will step on each other’s foot.

If we are talking about simply reading from standard input, that will work, but with a few quirks. First, without external synchronization it’s not known in which order processes are going to consume the input. It is even possible that process A grabs a few chunks from the input line, while process B grabs the rest.

Second, standard streams are buffered, therefore a process might consume more input than immediately obvious. E.g. the program reads a single line of input, but internally more data is read from the OS, since there’s no way to ask for bytes until the new line. The other process reading input simultaneously won’t get the input the other process consumed, even if the later only done it due to buffering and didn’t use the input.

To conclude, probably better to avoid having multiple processes consume input simultaneously.

Upvotes: 1

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