Why doesn't C have a non blocking sleep function like setTimeout in javascript

Question

sleep() blocks the running thread in C given x amount of seconds. If I'm not mistaking, this can be implemented in 2 ways. Either go in an infinite loop and check the current time with BIOS, if time>=timeout then end the loop.

Second way is to use a timer in CPU and let the timer do the counting async and not block the CPU thread.

Am I correct about the above 2 methods? if so why doesn't C have a function to implant the second way so we can have non-blocking "delays"?

Because there is no native support to asynchronous computing in C, you have to use a library such as pthread. — Havenard
– Havenard, Commented Jul 7, 2020 at 1:48
but theoretically speaking, sleep could have had an async version a swell right? nothing is stopping the hardware from doing it. — Dan
– Dan, Commented Jul 7, 2020 at 1:50
Depends on the hardware. C is designed to be used to program just about anything, from last gen games to 8-pin microcontrollers smaller than a grain of rice, so the language isn't tied to features that would limit it to advanced hardware. — Havenard
– Havenard, Commented Jul 7, 2020 at 1:54
The question seems to mix up two things: sleep() which blocks the program (or thread) but hopefully doesn't block the CPU (so that other threads or processes can run), and asynchronous timers like the non-ISO alarm() that let the program keep running and notify it after a certain length of time. It is entirely possible for the OS to implement sleep in your "second way" without a busy loop, by switching to another process (or halting the CPU) and letting a timer interrupt cause a switch back when the timeout expires. — Nate Eldredge
– Nate Eldredge, Commented Jul 7, 2020 at 1:59

rici · Accepted Answer · 2020-07-07 02:11:25Z

4

There's another way, which is the one which is usually behind a call to sleep(): tell the kernel scheduler to remove this process from the runnable set until the time has expired.

For the function which sets a timer and tells you when it is finished, you can start by looking at alarm() and pause(). Those aren't in the standard C library, but they have been in Posix for a very long time.

On Windows, you could look at SetTimer.

edited Jul 7, 2020 at 2:11

answered Jul 7, 2020 at 1:53

rici

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