man timer_gettime (2): per-process timers (REALTIME)

Other Alias

timer_getoverrun, timer_settime

LIBRARY

Lb librt

SYNOPSIS

In time.h Ft int Fn timer_getoverrun timer_t timerid Ft int Fn timer_gettime timer_t timerid struct itimerspec *value Ft int Fo timer_settime Fa timer_t timerid int flags const struct itimerspec *restrict value Fa struct itimerspec *restrict ovalue Fc

DESCRIPTION

The Fn timer_gettime system call stores the amount of time until the specified timer, Fa timerid , expires and the reload value of the timer into the space pointed to by the Fa value argument. The it_value member of this structure contains the amount of time before the timer expires, or zero if the timer is disarmed. This value is returned as the interval until timer expiration, even if the timer was armed with absolute time. The it_interval member of Fa value contains the reload value last set by Fn timer_settime .

The Fn timer_settime system call sets the time until the next expiration of the timer specified by Fa timerid from the it_value member of the Fa value argument and arms the timer if the it_value member of Fa value is non-zero. If the specified timer was already armed when Fn timer_settime is called, this call resets the time until next expiration to the value specified. If the it_value member of Fa value is zero, the timer is disarmed. If the timer is disarmed, then pending signal is removed.

If the flag TIMER_ABSTIME is not set in the argument Fa flags , Fn timer_settime behaves as if the time until next expiration is set to be equal to the interval specified by the it_value member of Fa value . That is, the timer expires in it_value nanoseconds from when the call is made. If the flag TIMER_ABSTIME is set in the argument Fa flags , Fn timer_settime behaves as if the time until next expiration is set to be equal to the difference between the absolute time specified by the it_value member of value and the current value of the clock associated with Fa timerid . That is, the timer expires when the clock reaches the value specified by the it_value member of Fa value . If the specified time has already passed, the system call succeeds and the expiration notification is made.

The reload value of the timer is set to the value specified by the it_interval member of Fa value . When a timer is armed with a non-zero it_interval a periodic (or repetitive) timer is specified.

Time values that are between two consecutive non-negative integer multiples of the resolution of the specified timer are rounded up to the larger multiple of the resolution. Quantization error will not cause the timer to expire earlier than the rounded time value.

If the argument Fa ovalue is not NULL the Fn timer_settime system call stores, in the location referenced by Fa ovalue , a value representing the previous amount of time before the timer would have expired, or zero if the timer was disarmed, together with the previous timer reload value. Timers do not expire before their scheduled time.

Only a single signal is queued to the process for a given timer at any point in time. When a timer for which a signal is still pending expires, no signal is queued, and a timer overrun will occur. When a timer expiration signal is accepted by a process, the Fn timer_getoverrun system call returns the timer expiration overrun count for the specified timer. The overrun count returned contains the number of extra timer expirations that occurred between the time the signal was generated (queued) and when it was accepted, up to but not including an maximum of Br q Dv DELAYTIMER_MAX . If the number of such extra expirations is greater than or equal to Br q Dv DELAYTIMER_MAX , then the overrun count is set to Br q Dv DELAYTIMER_MAX . The value returned by Fn timer_getoverrun applies to the most recent expiration signal acceptance for the timer. If no expiration signal has been delivered for the timer, the return value of Fn timer_getoverrun is unspecified.

RETURN VALUES

If the Fn timer_getoverrun system call succeeds, it returns the timer expiration overrun count as explained above. Otherwise the value -1 is returned, and the global variable errno is set to indicate the error.

Rv -std timer_gettime timer_settime

ERRORS

The Fn timer_settime system call will fail if:

Bq Er EINVAL: A Fa value structure specified a nanosecond value less than zero or greater than or equal to 1000 million, and the it_value member of that structure did not specify zero seconds and nanoseconds.

These system calls may fail if:

Bq Er EINVAL: The Fa timerid argument does not correspond to an ID returned by Fn timer_create but not yet deleted by Fn timer_delete .

The Fn timer_settime system call may fail if:

Bq Er EINVAL: The it_interval member of Fa value is not zero and the timer was created with notification by creation of a new thread ( sigev_sigev_notify was SIGEV_THREAD and a fixed stack address has been set in the thread attribute pointed to by sigev_notify_attributes

The Fn timer_gettime and Fn timer_settime system calls may fail if:

Bq Er EFAULT: Any arguments point outside the allocated address space or there is a memory protection fault.

STANDARDS

The Fn timer_getoverrun , Fn timer_gettime , and Fn timer_settime system calls conform to St -p1003.1-2004 .

HISTORY

Support for POSIX per-process timer first appeared in Fx 7.0 .