In fork() which will run first, parent or child?

Question

When the following code runs, I understand the parent and child both will run in parallel immediately after fork() is called.

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Answer 1

Apparently whatever scheduler you're running decides, and it can vary.

I can say from experience that if you assume that one of the two processes always runs first, you will introduce some very subtle race conditions. Either synchronize on something, like a special message on the pipe, or don't assume that either one runs first.