How to use nanosleep() in C? What are `tim.tv_sec` and `tim.tv_nsec`?
CPosixSleepC Problem Overview
What is the use of tim.tv_sec and tim.tv_nsec in the following?
How can I sleep execution for 500000 microseconds?
#include <stdio.h>
#include <time.h>
int main()
{
struct timespec tim, tim2;
tim.tv_sec = 1;
tim.tv_nsec = 500;
if(nanosleep(&tim , &tim2) < 0 )
{
printf("Nano sleep system call failed \n");
return -1;
}
printf("Nano sleep successfull \n");
return 0;
}
C Solutions
Solution 1 - C
Half a second is 500,000,000 nanoseconds, so your code should read:
tim.tv_sec = 0;
tim.tv_nsec = 500000000L;
As things stand, you code is sleeping for 1.0000005s (1s + 500ns).
Solution 2 - C
tv_nsec is the sleep time in nanoseconds. 500000us = 500000000ns, so you want:
nanosleep((const struct timespec[]){{0, 500000000L}}, NULL);
Solution 3 - C
500000 microseconds are 500000000 nanoseconds. You only wait for 500 ns = 0.5 µs.
Solution 4 - C
This worked for me ....
#include <stdio.h>
#include <time.h> /* Needed for struct timespec */
int mssleep(long miliseconds)
{
struct timespec rem;
struct timespec req= {
(int)(miliseconds / 1000), /* secs (Must be Non-Negative) */
(miliseconds % 1000) * 1000000 /* nano (Must be in range of 0 to 999999999) */
};
return nanosleep(&req , &rem);
}
int main()
{
int ret = mssleep(2500);
printf("sleep result %d\n",ret);
return 0;
}
Solution 5 - C
I usually use some #define and constants to make the calculation easy:
#define NANO_SECOND_MULTIPLIER 1000000 // 1 millisecond = 1,000,000 Nanoseconds
const long INTERVAL_MS = 500 * NANO_SECOND_MULTIPLIER;
Hence my code would look like this:
timespec sleepValue = {0};
sleepValue.tv_nsec = INTERVAL_MS;
nanosleep(&sleepValue, NULL);
Solution 6 - C
POSIX 7
First find the function: <http://pubs.opengroup.org/onlinepubs/9699919799/functions/nanosleep.html>
That contains a link to a time.h, which as a header should be where structs are defined:
> The
man 2 nanosleep
Pseudo-official glibc docs which you should always check for syscalls:
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
};
Solution 7 - C
More correct variant:
{
struct timespec delta = {5 /*secs*/, 135 /*nanosecs*/};
while (nanosleep(&delta, &delta));
}