c - how is `while(1)` optimized not to take all resources? -

suppose have code this:

while(1) {       scanf("%c", &key);       // if e or e, exit       if (key == 'e' ||  key == 'e')           break; } 

this not take resources of single core. just... "sits" there until presses e. question is: how runtime find out should not take resources of core waiting scanf? scanf special case in i/o , such os schedules out until key pressed? can somehow force whileing time say, adding a++ inside loop?

is scanf special case in i/o , such os schedules out until key pressed

that's happening. in case scanf blocking operation. is, if can't executed (nothing in input buffer) os puts process sleep, remembering wake when turns up.

can somehow force whileing time say, adding a++ inside loop

an a++ won't change anything. won't able peg cpu long have long-waiting blocking calls.

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until key pressed

in linux input "cooked". is, pressing single key isn't typically enough (you need hit return before process gets chance @ data).

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as basile correctly mentions in comments scanf may not block. if there's enough input in stdio buffer scanf return it. if not call read(2) can block.