make: Parallel Input
5.4.2 Input During Parallel Execution
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Two processes cannot both take input from the same device at the same
time. To make sure that only one recipe tries to take input from the
terminal at once, 'make' will invalidate the standard input streams of
all but one running recipe. If another recipe attempts to read from
standard input it will usually incur a fatal error (a 'Broken pipe'
signal).
It is unpredictable which recipe will have a valid standard input
stream (which will come from the terminal, or wherever you redirect the
standard input of 'make'). The first recipe run will always get it
first, and the first recipe started after that one finishes will get it
next, and so on.
We will change how this aspect of 'make' works if we find a better
alternative. In the mean time, you should not rely on any recipe using
standard input at all if you are using the parallel execution feature;
but if you are not using this feature, then standard input works
normally in all recipes.
Info Catalog
make: Parallel Output
make: Parallel