TimerAlarm(), TimerAlarm_r()

Send an alarm signal

Synopsis:

#include <sys/neutrino.h>

int TimerAlarm( clockid_t id,
                const struct _itimer * itime,
                struct _itimer * otime );

int TimerAlarm_r( clockid_t id,
                  const struct _itimer * itime,
                  struct _itimer * otime );

Arguments:

id

The timer type to use to implement the alarm; one of:

• CLOCK_REALTIME — the standard POSIX-defined clock. Timers based on this clock wake up the processor if it's in a power-saving mode.
• CLOCK_SOFTTIME — this clock is active only when the processor isn't in a power-saving mode. For example, an application using a CLOCK_SOFTTIME timer to sleep wouldn't wake up the processor when the application was due to wake up. This will allow the processor to enter a power-saving mode.

  While the processor isn't in a power-saving mode, CLOCK_SOFTTIME behaves the same as CLOCK_REALTIME.

• CLOCK_MONOTONIC — this clock always increases at a constant rate and can't be adjusted.

itime

NULL, or a pointer to a _itimer structure that specifies the length of time to wait.

otime

NULL, or a pointer to a _itimer structure where the function can store the old timer trigger time.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

These kernel calls set an alarm signal (SIGALRM) to be delivered to the thread waiting on the timer at the time specified by itime. If otime isn't NULL, the old timer trigger time is returned.

The TimerAlarm() and TimerAlarm_r() functions are identical except in the way they indicate errors. See the Returns section for details.

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Instead of using these kernel calls directly, consider calling alarm() or setitimer(). Because of the nature of time measurement, the signal might actually get sent later than the specified time. For more information, see the Tick, Tock: Understanding the Neutrino Microkernel's Concept of Time chapter of the QNX Neutrino Programmer's Guide.

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Alarm requests aren't stacked; only a single SIGALRM may be outstanding on a timer at one time. If you call TimerAlarm() while an alarm is outstanding, the alarm is reset to the new value passed in itime.

If itime is NULL, any previous alarm request is canceled, and no new alarm is set.

Blocking states

These calls don't block.

Returns:

The only difference between these functions is the way they indicate errors:

TimerAlarm()

If an error occurs, -1 is returned and errno is set. Any other value returned indicates success.

TimerAlarm_r()

EOK is returned on success. This function does NOT set errno. If an error occurs, any value in the Errors section may be returned.

Errors:

EAGAIN

All kernel timer entries are in use.

EINVAL

Invalid timer value id.

Classification:

QNX Neutrino

Caveats:

The alarm(), TimerAlarm(), and ualarm() requests aren't stacked; only a single SIGALRM generator can be scheduled with these functions. If the SIGALRM signal hasn't been generated, the next call to alarm(), TimerAlarm(), or ualarm() reschedules it.

See also:

alarm(), setitimer(), TimerCreate(), ualarm()

Clocks, Timers, and Getting a Kick Every So Often chapter of Getting Started with QNX Neutrino

Tick, Tock: Understanding the Neutrino Microkernel's Concept of Time chapter of the QNX Neutrino Programmer's Guide