alarm, ualarm - Sets or changes the timeout of interval
unsigned int alarm(
unsigned int seconds ); useconds_t ualarm(
unseconds_t interval );
Standard C Library (libc)
Interfaces documented on this reference page conform to
industry standards as follows:
alarm(), ualarm(): XSH5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Specifies a number of real-time seconds. Specifies a number
of real-time microseconds. Specifies the interval for
repeating the timer.
The alarm() function is used to obtain notification of a
timeout after the number of real-time seconds specified by
the seconds parameter has elapsed. At some time after seconds
seconds have elapsed, a signal is delivered to the
process. Each call resets the timer to the new value. A
value of 0 (zero) disables the timer. When the notification
signal is caught or ignored, no action takes place;
otherwise the calling process is terminated. The alarm()
function uses the ITIMER_REAL interval timer.
The ualarm() function is used to obtain notification of a
timeout after the number of real-time microseconds specified
by the useconds parameter has elapsed. When the
interval parameter is nonzero, timeout notification occurs
after the number of microseconds specified by the interval
parameter has been added to the useconds parameter. When
the notification signal is caught or ignored, no action
takes place; otherwise the calling process is terminated.
The ualarm() function is the simplified interface to the
setitimer() function, and uses the ITIMER_REAL interval
The alarm() and ualarm() functions are supported for multithreaded
Although the alarm() and ualarm() functions are reentrant,
it should be noted that just as the second of two calls
from a single thread to alarm() resets the timer, this is
also true if two calls are made from different threads.
If there is a previous alarm() request with time remaining,
the alarm() function returns a non-zero value that is
the number of seconds until the previous request would
have generated a SIGALRM signal. Otherwise, alarm()
returns 0 (zero).
The ualarm() function returns the number of microseconds
remaining from the previous ualarm() call. If no timeouts
are pending or if ualarm() has not previously been called,
ualarm() returns 0 (zero).
The alarm() function sets errno to the specified values
for the following conditions:
[Tru64 UNIX] The seconds parameter specifies a value
greater than 100,000,000.
[ Back ]