DESCRIPTION
The function clock_getres() finds the resolution (precision) of the specified clock clk_id, and, if res is non-NULL, stores it in the struct timespec pointed to by res. The resolution of clocks depends on the implementation and cannot be configured by a particular process. If the time value pointed to by the argument tp of clock_settime() is not a multiple of res, then it is truncated to a multiple of res. The functions clock_gettime() and clock_settime() retrieve and set the time of the specified clock clk_id.
The res and tp arguments are timespec structs, as specified in <time.h>:
struct timespec {
time_t tv_sec; /* seconds */
longtv_nsec; /* nanoseconds */
};
The clk_id argument is the identifier of the particular clock on which to act. A clock may be system-wide and hence visible for all processes, or per-process if it measures time only within a single process.
All implementations support the system-wide realtime clock, which is identified by CLOCK_REALTIME. Its time represents seconds and nanoseconds since the Epoch. When its time is changed, timers for a relative interval are unaffected, but timers for an absolute point in time are affected.
More clocks may be implemented. The interpretation of the corresponding time values and the effect on timers is unspecified.
Sufficiently recent versions of GNU libc and the Linux kernel support the following clocks:
