C nanosleep() Function

nanosleep function in C is used to suspend the execution of the program for a specific amount of time for nanoseconds. The function can be is in the <time.h> header in C. Another function to suspend the execution of the program is the sleep function which provides low-level resolution suspension but in nanosleep we have the advantage of pausing the program for nanoseconds i.e., it has high precision.

Syntax:

int nanosleep(const struct timespec *t1, struct timespec *t2)

Both requests and remaining are two addresses of type struct timespec. Both will have two members:

tv_sec, which is the number of seconds.
tv_nsec, which is the number of nanoseconds.

Note : The value of tv_nsec should be between 0 to 999999999 or else the program will give an error.

Return value: On successful execution, it returns the value 0 else it returns -1.

Errors occurring while using nanosleep():

The nanosleep() function shall fail if:

[EINTR] : interrupted by a signal.
[EINVAL] : The t1 argument specified a nanosecond value less than zero or greater than or equal to 1000 million.

Example:

// C Program to demonstrate
// use of nanosleep
#include <stdio.h>
#include <time.h>

int main()
{
    struct timespec remaining, request = { 5, 100 };

    printf("Taking a nap...\n");
    int response = nanosleep(&request, &remaining);

    if (response == 0) {
        printf("Nap was Successful .\n");
    }
    else {
        printf("Nap was Interrupted.\n");
    }
}

Output

Taking a nap...
Nap was Successful .

C++

// C Program to demonstrate
// use of nanosleep
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main()
{
    struct timespec remaining, request = { 1, 34 };
    printf("Running\n");

    for (int i = 0; i < 10; ++i) {

        printf("loop  %d\n", i);
        if (i == 4) {
            printf("Nap time ...\n");

            errno = 0;
            if (nanosleep(&request, &remaining) == -1) {
                switch (errno) {
                case EINTR:
                    printf("interrupted by a signal "
                           "handler\n");
                    break;

                case EINVAL:
                    printf("tv_nsec - not in range or "
                           "tv_sec is negative\n");
                    break;

                default:
                    perror("nanosleep");
                    break;
                }
            }
        }
    }

    exit(EXIT_SUCCESS);
}

Output

Running
loop  0
loop  1
loop  2
loop  3
loop  4
Nap time ...
loop  5
loop  6
loop  7
loop  8
loop  9

Example when Errors are generated:

C++

// C Program to demonstrate
// nanosleep errors
#include <errno.h>
#include <stdio.h>
#include <time.h>

int main()
{
    struct timespec remaining, request = {
        8, -98
    }; // giving negative value to generate error in output

    printf("Nap started ...\n");
    int response = nanosleep(&request, &remaining);

    if (response == 0) {
        printf("Nap was Successful .\n");
    }
    else {
        printf("Nap Interrupted ...\n");
        errno = 0;
        if (nanosleep(&request, &remaining) == -1) {
            switch (errno) {
            case EINTR:
                printf("interrupted by a signal handler\n");
                break;
            case EINVAL:
                printf("Value not in range or Value is "
                       "negative\n");
                break;
            default:
                perror("nanosleep");
                break;
            }
        }
    }
}

Output

Nap started ...
Nap Interrupted ...
Value not in range or Value is negative

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